8. Properties of Diesel
This section examines the main properties that specify quality for diesel. It follows the same format as the previous section for petrol.
Like petrol, there is a high degree of interdependence between certain properties and again, within a particular refinery, diesel specifications have flow-on effects for the production of other products.
Appendix C contains a description of how compression-ignition engines work and the diesel characteristics that are relevant to diesel engine performance.
8.1 Properties Currently Specified
8.1.1 Density
What Is It?
Density is a measure of a fuel's mass per unit volume. It is temperature dependent and for diesel fuel is normally referenced to 15°C. Diesel is made up of a mixture of many different hydrocarbon compounds of various densities and molecular weights, and thus the overall density is a function of the composition of the fuel. For this reason, density is strongly correlated with other fuel parameters, particularly cetane number, aromatics content, viscosity and the distillation characteristics (boiling range or volatility). Reducing the high end distillation temperatures (T85, refer Section 8.1.11) will reduce the maximum density by excluding the heaviest components.
Why Is It Important?
In diesel engines, fuel is injected directly into the combustion chamber using a volume based metering system (in most cases). The energy content of fuel is approximately proportional to the mass of fuel injected. Thus, for a constant volume injection system, variations in fuel density can result in variations in the energy content of the fuel injected. Consequently engine power, emissions and fuel consumption may be affected. In order to optimise the engine performance and exhaust emissions, fuel density must be controlled within a fairly narrow range.
Black smoke emissions from diesel engines occur primarily at full load operation. They normally arise when the mixture is over-rich or there is incomplete mixing of fuel and air. Limits on smoke emissions therefore limit the maximum power output of engines. Although there is some relationship between visible smoke and particulates, the optical and size characteristics, and number density of particles vary greatly, and hence the relationship between them is not well understood.
If the fuel being used is denser than the fuel for which the engine is calibrated, this may lead to generation of smoke through overfuelling. Conversely, lower density fuel should reduce the level of smoke, but will reduce power as well if the fuel injection system is not set up for that lower density. For a constant maximum power output (constant mass of fuel injected) volumetric fuel consumption will increase with lowering density and decrease with increasing density.
The volumetric quantity of fuel injected can also be used as a parameter in some advanced emission control systems such as exhaust gas re-circulation (EGR) so variations in fuel density may affect their efficiency.
Current New Zealand and International Specifications
| Specification | Density in kg/m³ at 15°C |
|---|
| | Min. | Max. |
|---|
| New Zealand | 810 | 860 |
| Euro 3 (2000) | 820 | 845 |
| World-Wide Fuel Charter | 820 | 860 (Cat.1 ), 850 (Cat. 2), 840 (Cat. 3&4) |
| Australia | 820 | 860 from 1 January 2002
850 from 1 January 2006 |
| Japan | Not specified |
The density range for fuel from the Marsden Point Refinery over the year 2000 was 826 - 859 kg/m³. Data from Australia indicates a wider range (812 - 870 kg/m³) has been typical in the past.
Why Regulate?
Reductions in the upper limit have generally been for the purposes of limiting heavier aromatic components, thereby reducing emissions, principally particulates. However, this effect is also achieved to some extent by control of the high end of the distillation curve (see T85, Section 8.1.11).
A narrower density range gives reduced emissions due to better control of air/fuel ratio.
Alignment with other specifications is desirable, as far as is practicable. As 90% of New Zealand's diesel is produced at the Marsden Point Refinery, the Australian timetable for density changes is less directly relevant to New Zealand. However, reducing the upper density limit will have major cost and so some trade-off may be needed in terms of both level and timing.
The opportunity should be taken to adopt the standards units for density - kg/m³ instead of the current kg/litre.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Density at 15°C: 810 kg/m³ minimum; 860 kg/m3 maximum | Immediate increase to 820 kg/m3 minimum |
| | Stage 1 reduction to 850 kg/m3 maximum |
| | Stage 2 reduction to 845 kg/m³ maximum |
Implications of Proposed Changes
- Changing the density specifications will alter the composition of the fuel and thus will generally affect most other fuel properties important to diesel engine performance and emissions, such as cetane number, aromatics content, volatility, viscosity and others.
- Narrowing the allowable density range will limit the range of crudes which the Marsden Point Refinery is able to process. A lower maximum density will result in more fuel oil being produced as heavier components are excluded from the diesel. Current fuel oil production already exceeds the market, requiring surpluses to be exported.
- These changes will reduce diesel production and flexibility and therefore impose some cost.
8.1.2 Appearance and Colour
What Are They?
Water and sediment in diesel fuel usually result from poor fuel handling and storage. The general appearance, colour and clarity are useful indicators of contamination. However, the small amount of water or solids required to give diesel a hazy appearance is usually insufficient to affect its performance.
The specifications currently include two visual tests:
- A check on appearance at a standard temperature of 15°C using test method ASTM D 4176(B);
- A comparison of colour against a standard chart using test method ASTM D 1500.
Why Are They Important?
Contamination with water and sediment can result in corrosion, blocking of filters, injection system wear and deposits in engines.
Current New Zealand and International Specifications
Many international specifications include specific limits on water and sediment, rather than only specifying appearance and colour as per the New Zealand specification. Water and sediment limits are also currently included in the NZRC and Refinery Users specifications (0.05% max. water by volume, 0.01% max. sediment by weight).
| Specification | Parameter | Test procedure | Specification |
|---|
| New Zealand | Appearance at 15°C | ASTM D4176(B) | Clear and bright |
| | Colour | ASTM D1500 | |
| Euro 3 (2000) | Water content | prEN ISO 12937:1996 | 200 ppm max. |
| | Total contamination | EN 12662 | 24 ppm max. |
| World-Wide Fuel Charter | Water content | prEN ISO 12937:1996 | 200 ppm max. |
| | Particulates | EN 12662 | 24 ppm max. |
| Australia (proposed)16 | Water and sediment | | 0.05% max. (by weight) ~ 500 ppm |
| Japan | General requirement that fuel should not contain water or precipitates |
Why Regulate?
If appearance is to be used as a quality standard, a reference temperature is necessary and a fixed reference (as opposed to ambient temperature) provides a consistent basis for quality checks. The current value of 15°C appears to be a good choice, reflecting an average ambient temperature for New Zealand. The current NZRC and Refinery User specifications already call for a lower test temperature (10°C).
The requirement to carry out the test at 15°C can cause difficulties with diesel from some Australian refineries where the fuel may appear hazy at this temperature but otherwise meets internal water and sediment specifications. Hence this reference temperature can be constraining on sources of imported supplies.
Appearance and colour are useful quick tests for fuel quality, so it is proposed to retain them. However it is also proposed that specific limits on water content and total contamination be added, in line with international specifications. These are discussed in more detail in Section 8.2.3.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Appearance at 15°C: Clear and bright | No change |
| Colour: (ASTM colour) 3.0 maximum | No change |
8.1.3 Cetane Number and Cetane Index
What Are They?
Cetane Number
The Cetane Number (CN) of a fuel is a measure of its propensity for autoignition. In practical terms the CN has a strong influence on the length of time from the start of fuel injection to the start of combustion in a diesel engine. The higher the CN, the shorter this ignition delay period. The CN affects the ease of starting, the combustion generated noise and the exhaust emissions of diesel engines.
Cetane (n-hexadecane), which ignites very easily, has a CN of 100, and heptamethyl nonane has a CN of 15. The CN of a fuel is the proportion of cetane in a mix of the two that has equivalent ignition characteristics when tested in a specified test engine. The test method is standardised in ASTM D 613. There is no test engine in New Zealand and the test itself has poor reliability and repeatability.
The CN is related to the aromatic content of the fuel and in turn to the fuel density. As the aromatic content decreases, and thereby the density, the CN will generally increase.
Cetane Index
Cetane Index (CI) is an estimation of the Cetane Number calculated from distillation data and density. As there are very few test engines in existence, CI is the more commonly used. The current specification requires this to be calculated using the method outlined in ASTM D 976, as follows:
CI = 454.74 - (1641.416 x p) + (774.74 x p²) - 0.554 x T50 + 97.803 x (log T50)²
p is the density in g/litre at 15°C
T50 is the mid-boiling point temperature in °C (the temperature at which 50% of the sample (by volume) has evaporated).
The relationship between CI and CN varies depending on the refining techniques and consequent composition of the fuel. Generally the difference between the two measures will be in the range ?2.
Cetane improving additives can be used to increase the CN by aiding the self-ignition of the fuel. They do not change the parameters on which the CI is based, so cetane improvers do not change the calculated CI.
Why Are They Important?
A higher CN reduces ignition delay and results in smoother combustion and lower combustion noise. It also improves the cold starting of diesel engines. An increase in CN produces a decrease in NOx emissions due to lower gas temperatures and pressures in the combustion chamber. Reductions in CO and hydrocarbon emissions have also been reported. These benefits are less marked in new engine designs. However benefits are not generally achieved above a CN of about 50.
If anything, fuel consumption will tend to increase slightly with an increase in CN. Lower CN fuels will contain more higher aromatics and heavier hydrocarbons and have a higher density, giving a lower volume of fuel for the same amount of energy.
Although there are uncertainties in the correlation between CN and CI, an increase in CN will cause a increase in CI.
Current New Zealand and International Specifications
| Specification | Cetane Number (min.) | Cetane Index (min.) |
|---|
| New Zealand | 45 | 47 |
| Euro 3 (2000) | 51 | 46 |
| World-Wide Fuel Charter | 48 (Cat. 1) - 55 (Cat. 3&4) | 45 (Cat. 1) - 52 (Cat. 3&4) |
| Australia | Not specified | 46 from 1 January 2002 |
| Japan | Not specified | Special No. 1 and No. 1 - 50, No. 2 - 45 |
| USA | 40 | |
Currently the CI for diesel from the Marsden Point Refinery averages 52 - 53 and as cetane improvers are not generally used, this is equivalent to a CN of 50 - 51. This is comparatively high by world standards.
The general trend in international specifications is for small increases in CN to improve engine performance and emissions, however the future specifications in Europe and the USA are not significantly higher than current New Zealand values.
Why Regulate?
Why Specify Cetane Number?
At present there is no CN test engine in New Zealand and only one in Australia so CN cannot easily be measured directly, but only inferred from the calculated CI. The ASTM D 613 test for CN is quite involved and relies heavily on the skill of the operator to obtain consistent results. Repeatability is poor. For these reasons, the current Australian proposal is to have no specification for CN at all and rely only on CI.
However, as CN is the parameter that directly reflects performance of diesel fuel in an engine, rather than CI, it seems logical that this should continue to be the main parameter specified, though the difficulty of measuring it necessitates the continued use of CI as a proxy. Development work is currently underway overseas to provide an easier and more reliable test for CN but it may take some years before such a method is available and accepted as an oil industry standard.
A progressive increase from the specified minimum CN of 45 to a minimum of 51 to align with European specifications would ensure that performance and environmental benefits of the present high CN diesel available in New Zealand are locked in.
Cetane Number vs. Cetane Index
The relationship between CI and CN depends on refining methods and feedstocks. Generally most New Zealand diesel is a mixture of straight run and hydrocracked distillates. It is noted that whereas in most other specifications CN is generally a few points higher than CI, the current New Zealand requirement is the reverse.
The relative values of CN and CI in the current specifications were originally set in 1988 based on the relativity observed at that time. Work carried out by the Ministry of Commerce in 1998 (MOC, 1999) measured the CN of over 80 samples collected throughout New Zealand and looked at the relationship between CN and CI. Typical New Zealand diesel sampled had a value of CI typically 1.5 to 2 points higher than CN, but the difference was quite variable; the average CI was around 53.2.
The study calculated CI using both the 2-parameter correlation (ASTM D 976) and a newer 4-parameter correlation (ASTM D4737). It was concluded that for diesel available in New Zealand, ASTM D 976 provided a better correlation with CN and so should be retained.
The specifications currently require a minimum CN of 45 or a minimum CI of 47, so the diesel only has to meet whichever condition is less onerous. As noted above, the actual CN and CI levels for New Zealand diesel are already much higher.
Setting an appropriate CI for diesel from the Refinery to meet the suggested targets for CN may be unobtainable for imported diesel where the CI could be lower than the CN. If the appropriate level and means of determining the CI required is left to fuel suppliers, there still needs to be a level set in the specifications for the purpose of fuel quality monitoring. The specified CI also needs to reflect whether CN improver additives are used.
It is proposed that diesel be required to meet both a minimum CN and a minimum CI value and that the present CI remain unchanged. Having both specifications will ensure that both the CN target is met and will limit the amount of cetane improver that can be used. The change is a balance between preserving the high CN diesel currently available in New Zealand and allowing flexibility in sourcing imported diesel.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
Cetane Number: 45 minimum
or | Immediate requirement to meet both cetane number and cetane index minima; increase cetane number to 49 minimum |
| Cetane Index: 47 minimum | Stage 1 increase cetane number to 51 minimum. |
Implications of Proposed Changes
The Marsden Point Refinery has a large hydrocracker so meeting higher Cetane Number targets is not expected to be a significant constraint.
Cetane improvers may be required to be added to imported diesel to achieve the proposed CN targets. Some allowance may be required in the carbon residue specification to cater for this (see Section 8.1.10).
8.1.4 Cold Flow Properties
What Are They?
Diesel fuel can have a high content of paraffins which will start to form wax crystals as the fuel is cooled. This can lead to blockages of fuel filters and interruption to fuel supply under cold conditions. Cold flow performance is a key requirement for diesel fuels.
Cloud Point
Cloud Point is the temperature at which wax crystals start to precipitate out and the fuel becomes cloudy. Cloud point is determined according to the test method specified in ASTM D 2500.
Cold Filter Plugging Point
Cold Filter Plugging Point (CFPP) is the lowest temperature at which the fuel can pass through a standard test filter under standard conditions. CFPP is more precise and is a better indication of fuel performance in an engine. The test method is specified in IP 309.
Cold flow properties depend on the proportion of waxy components in the diesel (controlled by the selection of crude oils and the refining and blending processes). Cold flow improving additives lower the cold filter plugging point by changing the size and shape of the wax crystals that form at cold temperatures. However, these additives generally do not change the cloud point.
Why Are They Important?
Inadequate cold flow performance will result in high viscosity at low temperatures, leading to difficulties with starting and blockage of fuel filters.
Current New Zealand and International Specifications
As cold flow properties are related to climatic conditions, a direct comparison with specifications in other countries is not particularly useful. Most international specifications include a range of grades corresponding to different ambient temperature ranges and or geographical regions. Current New Zealand specifications are:
| Property | Summer
(1 September to end-February) | Winter
(1 March to 31 August) |
|---|
| Cloud point °C | 4 max. | -6 max. |
| Cloud point or CFPP °C | | -6 max. |
The current specifications apply at the time of manufacture in New Zealand or, for imported fuel, at the time of discharge into port storage. Diesel for marine use may be summer grade at any time of the year.
The NZRC and Refinery User Company specifications in New Zealand are much more specific and have been developed over years of experience to suit the local conditions. There are four geographical areas as well as seasonal groupings within each. Both CFPP and Cloud Point are specified and the assigned values in some cases are lower than the regulatory specifications (3°C to -15°C). Generally this is believed to provide a satisfactory level of cold weather performance to New Zealand consumers.
For fuels without cold flow improvers, CFPP is normally 1 or 2°C below the Cloud Point. For New Zealand diesel the difference can be much more variable, with CFPP up to 10-15? lower than Cloud Point.
Why Regulate?
- The Cloud Point test is quite adequate for the fairly mild New Zealand climate. It is a relatively simple test and typically underestimates the low temperature performance of the fuel, particularly when low temperature performance additives are used. The CFPP test is a more realistic laboratory test procedure which closely correlates with vehicle operability tests. It is relevant for fuels both with and without cold performance additives.
- Both parameters are useful complementary measures and should be retained. However the current specification levels do not adequately cover the range of conditions encountered in New Zealand; a -6°C cloud point or CFPP which meets the specifications would provide inadequate protection for Southland winter conditions.
- Ensuring adequate cold flow properties for a given season and location is primarily the suppliers responsibility and there needs to be sufficient flexibility to allow for variations from year to year, both in temperature and timing of specification changes. This specification is currently regulated at the time of manufacture or, for imported diesel, the date of discharge at New Zealand ports. This is due to the difficulty of ensuring product specifications at the pump during change over dates.
- Given the annual seasonal variations, it may be difficult to actually regulate for all circumstances without being too constraining. The consumer is already protected to some degree by the requirement to provide a fuel that is fit for purpose at the point of delivery, and this provision is being strengthened in the regulations (refer Section 9.2). Industry seasonal and geographical self-regulation appears to have generally worked well in the past.
- However, the current specifications need to be updated to reflect reality, and on balance, it is considered that a degree of regulation needs to be maintained. It is therefore proposed that changes to the regulations incorporate aspects of the industry standards. In particular, the maximum CFPP for the lower North Island and all of the South Island will be changed from -6°C to -9°C, providing a higher degree of cold weather protection for residents of those areas.
- It is also proposed that Cloud Point and CFPP should apply at the point of retail sale, as do all the other specifications. These properties are essential for consumer protection, and the regulations should ensure that consumers are supplied with appropriate fuel at all times during the year. To help facilitate the change between summer and winter seasons, spring and autumn periods are proposed, as outlined in the table.
- The current test method for Cloud Point is ASTM D 2500. An alternative test method, ASTM D 5773 uses an automated instrument with a constant cooling rate and so is more accurate, reliable and reproducable.
- The recent problems with plugging of diesel filters may be related to the effect of a particular additive on the ability of the fuel to be filtered at low temperatures. This problem was not detected by the normal cold flow tests (neither the regulatory requirements nor the stricter industry ones). It is therefore proposed that to ensure adequate filterability, a filter blocking test be added to the specifications (see Filter Blocking Tendency, Section 8.2.5).
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Summer: | Cloud Point: 4°C maximum |
| Immediate: Change to seasonal and geographical limits (see table). |
| Winter: | Cloud Point: -6°C maximum |
| Change Cloud Point test to ASTM D 5773 |
| or | Cold Filter Plugging Point:
-6°C maximum |
| Introduce a new filterability test (IP387) |
Proposed Seasonal and Geographical Limits
| Upper North Island |
|---|
| Summer | 1 October - 31 March | Cloud Point maximum 4°C |
| Rest of Year | 1 April - 30 September | Cloud Point maximum -1°C
Cold Filter Plugging Point maximum -6°C |
| Lower North Island and all of South Island |
|---|
| Summer | 1 October - 31 March | Cloud Point maximum 4°C |
| Autumn | 1 April - 30 May | Cloud Point maximum -1°C
Cold Filter Plugging Point maximum -6°C |
| Winter | 1 June - 31 August | Cloud Point maximum -1°C
Cold Filter Plugging Point maximum -9°C |
| Spring | 1 September - 30 September | Cloud Point maximum -1°C
Cold Filter Plugging Point maximum -6°C |
8.1.5 Viscosity
What Is It?
Viscosity is a measure of a fuel's resistance to flow. It affects the performance of diesel fuel pumps and injection systems. Viscosity is dependent on fuel composition and so is reflected in the distillation parameters, density and cold flow properties.
The current test method, ASTM D 445, measures the kinematic viscosity at 40°C in centistokes (cSt - equivalent to mm²/sec).
Why Is It Important?
High viscosity can reduce fuel flow rates, resulting in insufficient fuel flow. A very high viscosity may cause fuel pump distortion.
Low viscosity will increase leakage from the pumping elements within the pump, and this can also result in insufficient fuel delivery and hot starting difficulties. Wear may also increase with low viscosity as lubricity tends to decrease with viscosity. As the viscosity of a fluid is temperature dependent, it is necessary to minimise the allowable range in order to optimise engine performance.
The viscosity range needs to be maintained with a reasonable range to ensure that the spray pattern generated by the fuel injectors is well controlled.
Current New Zealand and International Specifications
| Specification | Kinematic viscosity at 40°C in mm²/s |
|---|
| | Min. | Max. |
|---|
| New Zealand | 1.5 | 5.0 |
| Euro 3 (2000) | 2.00 | 4.50 |
| World-Wide Fuel Charter | 2.00 | 4 - 4.5 |
| Australia (from 1January 2002) | 2.00 | 4.50 |
| Japan | 1.7 - 2.517 | Not specified |
| USA | 1.9 | 4.1 |
The current NZRC and User Company specification limits are 1.9 - 4.5 mm²/s.
Why Regulate?
Some degree of regulation probably needs to be retained for consumer protection, though viscosity is very dependent on other parameters.
Units should be standardised on mm²/s rather than cSt, although the numerical value is equivalent.
Alignment with European specifications (min. 2.0 mm²/s, max. 4.5 mm²/s) would give a tighter range for better engine performance. Australia will introduce these limits from January 2002.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Viscosity at 40°C: 1.5 mm²/s minimum; 5.0 mm²/s maximum | Immediate reduction to 4.5 mm²/s maximum |
| | Stage 1 increase to 2.0 mm²/s minimum |
A tighter range of viscosity would improve engine performance, and the Stage 1 proposal will align with European and Australian specifications. The proposed ranges are not particularly constraining as diesel available in New Zealand currently achieves the proposed immediate reduction.
8.1.6 Flash Point
What Is It and Why Is It Important?
The flash point is the lowest temperature at which the vapour above a liquid will ignite when exposed to a flame (or other ignition source with sufficient energy). It is a measure of both volatility and flammability. Flash point is important primarily from the standpoint of safe handling and storage of fuel. It is used to classify flammable liquids and therefore affects the design of equipment and the control of potential ignition sources.
Flash point is a reflection of the volatility of the diesel and is therefore set by distillation parameters. It does not affect engine performance directly.
Current New Zealand and International Specifications
The current New Zealand specification is 61°C minimum. At this level, diesel is not classed as a flammable liquid for the purposes of classification under the New Zealand Dangerous Goods Regulations nor is it classified as Dangerous Goods for transport by land or sea. Under the new HSNO (Hazardous Substance and New Organisms) Regulations it will be classified as Group 3.1D (Flammable Liquids - Low Hazard).
Both the World-Wide Fuel Charter and the European specifications specify a minimum flash point of 55°C. Japan specifies a minimum of 45 or 50°C, dependent on the grade (which in turn depends on climatic conditions). The Australian limit is 61.5°C.
Why Regulate?
The current minimum specified flash point is consistent with its classification and controls under the existing Dangerous Goods Regulations (still operative under the HSNO transitional provisions) and the new HSNO requirements. It should therefore be retained at its current value.
As flash point is such an important parameter for safe storage and handling, and given that diesel is so widely used, the requirement for diesel to meet the flash point specification should be a blanket one applying to all fuel supplied, not just fuel for retail sale. This is not a current requirement in the New Zealand specifications and appears to be an anomaly.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Flash Point: 61°C minimum applies to fuel sold by retail | Immediate: 61°C minimum applies to all diesel fuel |
The Regulations currently require only diesel sold by retail sale to meet the specified limit. The proposed change will ensure all diesel fuel conforms to this requirement.
8.1.7 Sulphur
Sulphur occurs naturally in crude oils and must be removed to an acceptable level during the refining process. Sulphur in diesel fuel contributes to formation of particulate matter (PM) in engine exhaust and affects the performance of vehicle emissions control equipment. It therefore has an indirect effect on emissions of CO, hydrocarbons and NOx.
Diesel fuel containing 500 ppm is generally referred to as Low Sulphur Diesel (LSD). Fuel containing 50 ppm sulphur or lower is referred to as Ultra Low Sulphur Diesel (ULSD). "Sulphur-free" diesel generally refers to levels below 10 ppm.
Lower sulphur levels in diesel can be achieved by using a combination of lower sulphur feedstocks and sulphur removal. Hydrodesulphurisation of diesel uses hydrogen to release the sulphur from the feed and form H2S which is removed and treated to recover the sulphur. A similar process occurs in hydrocracking.
The test method currently specified in the Regulations for sulphur in diesel is IP 242.
Why Is It Important?
Sulphur in diesel contributes to the formation of particulate matter (PM) in engine exhaust. The impact of sulphur on particulate emissions is complex, but generally well understood. Sulphur has no direct effect on the other regulated emission species. A small proportion of the sulphur in the fuel is oxidised to sulphates that contribute to the particulate matter emitted from diesel exhaust. The sulphates absorb water that adds to the mass of particulate matter and also increase the retention of organic compounds in the particulate matter.
As PM emissions are linked to health problems, in particular respiratory conditions, their reduction is a primary driver to reduce high (>500 ppm) sulphur levels in diesel fuel. Studies show that reductions of sulphur content from 3000 ppm to 500 ppm would reduce PM emissions by 10 - 15% directly. Further reductions in sulphur would produce minimal incremental direct benefit. As PM is made up of a variety of compounds other than sulphur, reducing sulphur to zero would not reduce PM to zero.
However, sulphur also affects the performance of existing diesel engine exhaust after-treatment oxidation catalysts, and inhibits emerging diesel exhaust gas treatment technology such as NOx absorbers and particulate filters. Oxidation catalysts used to reduce CO and hydrocarbons, and the catalyst used in particulate trap technology are very efficient at converting SO2 into sulphates. Current European technology light duty vehicles are often fitted with oxidation catalysts and operation of these on current New Zealand high sulphur diesel can lead to greatly increased PM emissions above the level which these same vehicles would operate without a catalyst. The sulphur can also either impair or totally block catalyst performance.
Current New Zealand and International Specifications
| Specification | Maximum allowable level |
|---|
| New Zealand | 3000 ppm (but no limits on fuel for marine use) |
Euro 3 (2000)
Euro 4 (2005) | 350 ppm
50 ppm
10 ppm to be available from 2005 onwards, and required in all diesel by 2011 (proposed) |
| World-Wide Fuel Charter | 5000 ppm (Cat. 1), 300 ppm (Cat. 2 & 3)
5 - 10 ppm (Cat. 4) |
| Australia | 500 ppm from 31 December 2002
50 ppm from 1 January 2006 |
| Japan | 500 ppm
50 ppm from end 2004 (proposed) |
| USA | 500 ppm for on-road diesel (except California - all diesel)
15 ppm from 2006 |
90% of New Zealand's diesel is produced at the Marsden Point Refinery. The same grade of diesel is used for both automotive and marine fuel. However this has only been the case since 1998 and was implemented primarily for logistics and distribution reasons. For diesel tested in New Zealand in 1998/1999 the average sulphur level was around 2000 ppm with a range of 1100 - 2700 ppm.
In the United Kingdom and some other EC countries, government incentives for cleaner fuels have lead to ULSD becoming available well ahead of the Euro 4 timetable. 10 ppm diesel (City Diesel) has been available in Sweden for a number of years. It is understood that Germany now intends to move to 10 ppm diesel by 2008. The introduction of sulphur-free diesel throughout Europe has been the subject of recent European Commission proposals (refer Section 5.3.3).
In Australia, where new sulphur targets have now been finalised, one of the major suppliers is looking to use a combustion improver to provide a reduction in PM formation equivalent to that achieved through sulphur reduction. This is an alternative to direct sulphur reduction, being proposed as an interim measure to meet the Australian timetable for fuel quality changes. A protocol for assessing the performance of such additives, as a basis for possible approval, has been agreed with Environment Australia (EA, 2000d).
Why Regulate?
Health and Environment
From a health perspective, particles smaller than 10 microns diameter (PM10) are of greatest concern as they can enter the lungs. Attention is also being focussed on particulates smaller than 2.5 microns (PM2.5). Studies show that PM10 levels in Christchurch are associated with increases in daily mortality. While diesel engine emissions are not the only source of particulates in our urban air, studies in both Auckland and Christchurch show that they can be a significant contributor.
A direct reduction of PM emissions from existing vehicles can be achieved by reducing sulphur levels to around 500 ppm. Diesel oxidation catalysts which remove CO and hydrocarbons also typically require a maximum level of 500 ppm sulphur to work effectively.
Further reductions in sulphur levels below 500 ppm will contribute only a small amount to reducing PM emissions directly, but will permit the use of new and emerging emissions control technology (such as 2-way and de-NOX catalysts, continuously regenerating particulate traps and on-board diagnostics) to further reduce PM and other emissions.
Regulators in Europe and the USA are moving to specify ULSD (50 ppm or less) in order to enable the adoption of this technology to meet future emissions regulations. ULSD is becoming more widely available in Europe with refineries moving to meet Euro 4 levels (2005) well ahead of the target, in response to incentives. It is inevitable that within the next 5 - 10 years, vehicle technology will demand levels of sulphur in diesel of 50 ppm or lower and that ULSD will become commonplace.
Ultimately these fuels will have to become widely available on the New Zealand market within this timeframe, so we have to identify strategies for achieving this. As the main producer of diesel used in New Zealand, it seems logical that the Marsden Point Refinery acquires the capacity for meeting this need.
Consumer Protection
Current levels of sulphur affect the performance of emissions control equipment in new light diesels now coming into the market in Europe, such as some of the newer model Peugeot diesels for example, and are likely to prevent these vehicles being imported into New Zealand until LSD is available nationwide.
Removal of sulphur from diesel reduces its natural lubricity which can cause increased wear in fuel pumps and other engine components. This problem was first identified when ULSD was first introduced in Sweden, but minimum lubricity levels can be achieved through the use of suitable additives. Lubricity tests are now commonly being included in many diesel specifications elsewhere and a similar test is proposed for New Zealand (refer Section 8.2.4).
LSD may also have a lower electrical conductivity - insufficient conductivity can lead to a build-up of static charge during transfer (filling bulk storage tanks, road tankers and vehicle fuel tanks). This can be corrected through the use of additives and is primarily an operating requirement for industry, so it is not proposed to regulate at this time (refer Section 8.2.6).
Sulphur reduction may also assist in allowing an increase in engine oil change cycles by reducing the sulphuric acid loading in oil. However, engine design is also a significant factor in lengthening oil change intervals by giving cleaner combustion and lower soot loading of oil.
Hydrodesulphurisation can increase paraffinic content of diesel by saturating olefinic compounds, and this would tend to increase the CN a little, which is an additional benefit.
The current test method for sulphur is not sensitive enough for low sulphur levels - a new method, ASTM D 5453 is proposed. This would be the same as that proposed for sulphur in petrol (see Section 7.1.6).
Timing for Sulphur Reduction
Low sulphur diesel is already available in New Zealand on a limited basis. BP's LSD which contains around 500 ppm maximum sulphur was introduced in Christchurch in December 2000. This product is currently produced at the Marsden Point Refinery. However the Refinery's diesel HDS capacity is limited and it is unable to provide the total New Zealand diesel market with LSD using the current balance of crude feedstocks.
There is increasing public pressure for the immediate reduction of sulphur levels in diesel on a wider basis . The available options are being assessed, along with the implications, of adopting either a national specification or regional limits where vehicle emissions are a major contributor to poor local air quality. Immediate changes are therefore still under consideration.
In the medium term, a 2-stage reduction is proposed. Reduction to 500 ppm will directly reduce particulate emissions. Further reductions (to 50 ppm or less) will be needed to allow the use of new emissions-control technology for diesel vehicles. This technology is very sensitive to sulphur, and sulphur levels lower than 50 ppm are likely to be required for these vehicles.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
Sulphur: 3000 ppm maximum (mg/kg)
(Diesel for marine use is exempted from this Regulation) | Immediate - reduction under consideration. Change test method to ASTM D 5453 |
| | Stage 1 reduction to 500 ppm maximum |
| | Stage 2 reduction to 50 ppm maximum |
| | Signal ultimate requirement for sulphur free diesel (<10 ppm) |
Implications of Proposed Changes
- The timetable proposed recognises that refineries in the Asia-Pacific region are not all able to meet lower sulphur requirements.
- For the Marsden Point Refinery, meeting even Stage 1 specifications will require additional sulphur-removal capacity, at significant cost. While it may be possible to largely achieve some reductions through selection of lower sulphur (sweeter) feedstocks, this would have a significant impact in terms of higher feedstock costs, and the sweeter crudes required would produce lower cetane number diesel and higher benzene petrol streams.
- Supplying a much larger part of the New Zealand market with imported LSD is a possible option, but this product commands a premium and would also result in less than optimal use of the Marsden Point's capacity, potentially affecting its viability.
- The Refinery also needs to plan for Stage 2 and beyond, while ensuring that investment to meet short-term goals is not wasted. Estimates based on overseas figures indicate that additional hydrodesulphurisation plant to meet 50 ppm sulphur or lower could cost in the order of NZ$120-150 million. There are long lead times for processing equipment and refinery shutdowns need to be programmed to allow major construction works. Production of the necessary hydrogen for new or expanded hydrodesulphurisation capacity is itself an energy intensive process with greenhouse gas implications.
- Any reduction in sulphur which results in increased cost to the consumer will also penalise non-vehicle users, who comprise a significant share of the market, unless there is some segregation of product. However segregation between road and non-road users (except possibly marine) is unlikely to be workable in the small New Zealand market.
- It is proposed to retain the current exemption for marine diesel but future limits may be considered in line with European Commission directives and International Maritime Organisation (IMO) initiatives. The EC currently imposes a maximum limit of 2000 ppm on diesel for marine use in EC waters. IMO proposals mainly relate to the much higher levels of sulphur in fuels oils and controls on marine engine design to achieve emission targets for NOx. In recent years, none of the suppliers in New Zealand has marketed a separate marine grade, so all diesel supplied is automotive grade and meets the sulphur limit specified. Given that the primary driver for sulphur reduction is urban air quality, there may in the future be advantages to once again supplying a higher sulphur marine diesel.
8.1.8 Copper Strip Corrosion
What Is It?
As for petrol, this test is a measure of the corrosivity of the fuel to metals. Corrosion can affect metallic components in vehicle fuel systems, dispenser pumps and fuel storage systems. The same test procedure, ASTM D 130, is used.
Current New Zealand and International Specifications
The New Zealand specification calls for the test to be performed for 3 hours at 100°C (vs. 2 hours for petrol). A common test limit for petrol and diesel has been adopted in the European specifications using a lower temperature test (50°C) for 3 hours.
The neutralisation or acid number is a further measure of the fuel's acidity and ability to cause corrosion and is used in some international specifications. A test for this is currently included in the NZRC and Refinery Users specifications.
Why Regulate?
As for petrol, some measure of corrosivity needs to be retained to provide protection for fuel tanks, dispenser pumps and vehicle engine components.
Reducing the current test from 100°C to 50°C would reduce its severity, and in theory at least, the level of corrosion protection provided. Whether there is good reason to have different test conditions for petrol and diesel is questionable, unless the corrosion risk is clearly different, either due to the nature of the fuel itself or the materials it comes into contact with. Like the corrosivity test for petrol, testing at the lower temperature would be safer to carry out and align with international practice. On balance a standardised test (3 hours at 50°C) would be beneficial. No change to the test method or the required corrosion test standard is proposed.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Copper strip corrosion test: 100°C for 3 hours, then compare with a reference sample | Immediate: Copper strip corrosion test: 50°C for 3 hours, then compare with a reference sample |
8.1.9 Ash
What Is It and Why Is It Important?
Ash refers to the small amounts of non-combustible ash forming compounds such as suspended solids and soluble organometallic compounds which occur in crude oil and petroleum products.
Depending on size, these compounds can contribute to fuel system wear and filter and injector nozzle plugging. The metals can cause corrosion of certain high temperature alloys such as found on diesel engine valves, and lead to increased deposit levels.
Current New Zealand and International Specifications
The current specification is 0.01% ash by mass maximum, which is consistent with European specifications.
Why Regulate?
For any characteristic of fuel which may affect engine performance and condition in the long term rather than one that is immediately traceable to a fuel quality problem or particular fuel source, some level of consumer protection needs to be retained. No change is proposed.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Ash: 0.01% maximum by mass | No change |
8.1.10 Carbon Residue
What Is It?
This property is a measure of the tendency of diesel to form carbonaceous deposits in engines, which can result in hot spots leading to stress, corrosion or cracking of components. The deposits of most concern are those which build up in the nozzles of fuel injectors. The amount of carbon in fuel can be correlated with a tendency to form deposits, hence the use of a Carbon Residue test. The test is performed on the residual volume after 90% of the fuel has been boiled off (10% residual).
Methods in common use include:
- Ramsbottom IP 14/94 (ASTM D 524-94) (currently specified in the Regulations)
- Conradson IP 13/94 (ASTM D 159-95)
- Micro method MCRT IP 389 (ASTM D 4530) - equivalent to the Conradson method.
Detergents and deposit control additives are used to prevent deposit formation in fuel system components. Some may also be capable of removing existing deposits in the engine combustion chamber.
Current New Zealand and International Specifications
| Specification | Test method | Limit |
|---|
| New Zealand | Ramsbottom | 0.20 % mass max. |
| Euro 3 (2000) | EN ISO 10370 / IP 398 (micro methods) | 0.30 % mass max. |
| World-Wide Fuel Charter | EN ISO 10370 & ASTM D4530-93 (micro methods) | 0.3 - 0.2 mass max. (Cat. 3&4) |
| Australia (proposed)18 | | 0.16% mass max. |
| Japan | | 0.1% mass max. |
Why Regulate?
For properties of diesel which may detrimentally affect engine performance and condition over time rather than immediately, some level of consumer protection needs to be retained.
Micro carbon methods (such ASTM D 4530) are now widely in use for determination of carbon residue. These are more precise and capable of detecting lower levels than the current method specified. Adoption of this method would align with the European specifications but it is suggested that an appropriate limit on a 10% residuum is 0.10% mass max, not 0.3% max as in those specifications. The Marsden Point Refinery also routinely uses this method.
However, if particular types of cetane improvers are being used, these can give an abnormally high result. In this case the presence of a cetane improving additive needs to be confirmed as the cause, using a test such as ASTM D 4046.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Carbon Residue: Ramsbottom test on heaviest 10% of a sample; 0.2% maximum by mass | Immediate replacement with MCR test (test method IP 398 (ASTM D 4530)) with 0.1 % maximum by mass |
8.1.11 Distillation - T85
What Is It?
The distillation curve (temperature vs. percentage volume recovered) characterises the volatility of the fuel. T85 is the temperature at which 85% of the fuel sample has boiled off. For diesel, the most important distillation characteristics are the temperatures at the top end of the range (T85, T90, T95 etc.) as these provide a measure of the proportion of heavier components, and correlate closely with levels of aromatics in particular. As the density is dependent on the composition of the fuel, the distillation characteristics affect the density as well as the viscosity and Cetane Index. Thus the distillation curve is an important factor in the control of fuel quality.
This property is controlled by adjusting the cut point between diesel and heavier fuel oils. The distillation is carried out in accordance with test method ASTM D 86.
Why Is It Important?
The heavier components in diesel have more potential for incomplete vaporisation and combustion, resulting in increased smoke or soot. Specifying lower high end temperatures reduces the proportion of these heavy components, giving cleaner burning. It may also reduce the density and the viscosity of the fuel as these properties are closely linked. However, some studies suggest that where the effects of volatility can be decoupled from the other fuel parameters, the impact on emissions of changing the high end of the distillation curve may not be that significant.
Current New Zealand and International Specifications
Different jurisdictions specify different distillation parameters, so direct comparisons are not always easily made, as shown below. However, there is an international trend towards lower high end boiling points for diesel, with the European T95 value being the same as the current New Zealand T85 value. T95 is becoming a more standard indicator as well.
| Specification | Parameter | Limit |
|---|
| New Zealand | T85 | 350°C max. |
| Euro 3 (2000) | E25019
E350
T95 | <65 % by volume
85% by volume min.
350°C max. |
| World-Wide Fuel Charter | T90
T95
Final boiling point | 340°C (Cat.1) - 320°C (Cat. 3&4)
355°C (Cat.1) - 340°C (Cat. 3&4)
365°C (Cat.1) - 350°C (Cat. 3&4) |
| Australia | T95 | 370°C max. from 1 January 2002
360°C max. from 1 January 2006 |
| Japan | T90 | 330 - 360? C depending on cold weather class |
| USA | T90 | 338°C max. |
Why Regulate?
Reductions in high end distillation are aimed primarily at achieving environmental benefits.
- A change to T95 at 370°C is approximately equivalent to the current T85 of 360°C for diesel from the Marsden Point Refinery. Doing this immediately would align with international practice without a significant change in fuel quality.
- T95 would have to be set lower than 370°C to provide any benefit in terms of removing heavier fractions and a reduction to 360°C is proposed at Stage 1. This will reduce aromatics and emissions of CO, HC and PM (mainly through reducing density). It will also reduce the overall toxicity (mutagenicity and carcogenicity) of emissions, as well as the viscosity, and may increase the Cetane Number.
- Use of a T95 distillation point limits the heavier ends, but if used as a replacement for T85 would not limit the T85 - T95 fraction. Setting other limits such as T50, or a lower value of T85 as well allows for tighter control of the proportion of heavier compounds. However, separate specifications such as total aromatics and PAH limits can also control these components, so it is not proposed to regulate further at this stage.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
Distillation:
T85: 350°C maximum
T95 not specified | Immediate removal of T85 specification and replacement with a maximum T95 of 370°C
Stage 1 reduction in maximum T95 to 360°C |
Implications of Proposed Changes
As more of the heavier components are removed this reduces the yield of diesel from a given feedstock and increases the production of fuel oil. There is a cost impact associated with any change that reduces yield and creates more heavy material. Hence the reduction of T95 to 360°C is timed to coincide with a similar change in Australia.
8.2 Properties Currently Not Specified
The following properties for diesel are not currently included in the New Zealand specifications but have appeared elsewhere in specifications or their inclusion is under discussion. Therefore their significance is discussed here.
8.2.1 Polyaromatic Hydrocarbons (PAH)
What Are They?
Aromatics containing multiple benzene rings are known as polyaromatic hydrocarbons or (PAHs or PCAs). Whereas aromatics containing a single benzene ring are an issue with petrol, it is primarily PAHs which are of concern with diesel. Current evidence suggests that only the PAHs contribute to particulate emissions, so it is only these and not total aromatics in diesel which need be considered for regulation. Some PAHs such as benzo(a)pyrene are known to be carcinogenic.
PAHs are predominantly present in the heavier ends in diesel so their content is controlled through the distillation parameters such as T85 and T95.
Why Are They important?
Data on the impact of PAHs on regulated emissions are fairly sparse. However, it appears that there are consistent trends with decreased PAH resulting in decreased hydrocarbon and NOx emissions but no impact on CO. Reduced PAH has a significant benefit on PM for older engines which produce higher levels of particulates. For modern lower emission engines, the impact is little to none. These effects are attributed to the higher flame temperature and higher C:H ratio of aromatics. For this reason, there is a trend in international fuel specifications to placing limits on aromatics and PAHs in particular.
Current New Zealand and International Specifications
| Specification | Limit |
|---|
| Euro 3 (2000) | 11% max. by mass |
| World-Wide Fuel Charter | 25% max. by mass total aromatics (15% Cat. 3 & 4)
5% max. by mass PAH (2% Cat. 3 & 4) |
| Australia | 11% max. by mass from 1 January 2006 |
Why Regulate?
No data are available on current PAH levels in New Zealand diesel (either imported or from the Marsden Point Refinery). Available information indicates positive benefits in emissions reduction from reducing PAHs in diesel and this has been the basis for introduction of limits in European and other specifications.
An ambient air quality guideline of 0.30 ng/m³ (0.0003 µg/m³) for benzo(a)pyrene has been recommended for New Zealand (refer Appendix E). Based on the limited data available, there is a significant chance that existing (possibly background) levels exceed this recommendation (MfE#13, 2000). However, diesel-fuelled vehicles are not the primary source of PAHs in ambient air.
Reducing PM emissions through control of PAHs will have environmental benefits, However, the reduction in PM emissions achieved through proposed changes to T95 and sulphur levels are likely to outweigh any immediate changes to PAH levels.
Indications are that a maximum limit of 11% mass for diesel could be achieved on the same timetable as Australia (2006) or possibly earlier (2003) for diesel from the Marsden Point Refinery without being unnecessarily constraining and this would allow early alignment with European specifications. In the meantime, a watching brief should be maintained as information on New Zealand ambient air concentrations and sources of PAHs improves.
New Regulations proposed
| Current Regulations | Proposed changes |
|---|
| PAHs: not currently regulated | Stage 1 reduction to maximum PAH of 11% by mass, to apply to all diesel
(Test method ASTM D 5186 or IP 391) |
What Are the Implications of These Changes?
As PAHs are higher density components of diesel, reduction of T95 limits and maximum density will effectively reduce the PAH content. As already noted, this reduces the overall yield of diesel and these components then have to be used elsewhere, either in heavier products or be upgraded to lighter components through further processing, so there are some cost implications in imposing any reduction in PAHs in diesel over present levels.
8.2.2 Oxidation Stability
What Is It and Why Is It Important?
As for petrol, the oxidation stability is a measure of the fuel's resistance to degradation by oxidation. Oxidation of diesel fuel can result in the formation of gums and sediments, causing plugging of filters and engine deposits. It may also lead to a darkening in colour of the fuel though this is not a problem in itself.
In the oxidation stability test, oxygen is bubbled through the fuel at an elevated temperature for a fixed time, then it is cooled and the insolubles filtered off and weighed.
For diesel fuels with low levels of natural anti-oxidants, a satisfactory level of stability can be achieved with the use of anti-oxidant additives.
Current New Zealand and International Specifications
Oxidation stability is not currently regulated for diesel, though it is for petrol (by specifying the Oxidation Stability Induction Period). The European specifications and World-Wide Fuel Charter both set a maximum limit of 25 g/m³ and it is understood that a similar limit is proposed for the Australian operability specifications.
Why Regulate?
Severe hydrotreating of crudes to produce low sulphur diesels can remove some of the natural anti-oxidants in diesel creating potential for instability problems when such fuel is stored for long periods. Therefore with the wider introduction of lower sulphur diesels in the future, oxidation stability should be regulated for consumer protection.
The immediate introduction of an oxidation stability test is proposed with a specified level in line with international specifications and using ASTM D 2274-94 as the test method.
New Regulations Proposed
| Current Regulations | Proposed changes |
|---|
| Oxidation Stability: not currently regulated | Immediate introduction of an oxidation stability test: 25 g/m³ maximum (test method ASTM D 2274 (Accelerated Method)) |
8.2.3 Water Content and Total Contamination
As noted in Section 8.1.2 it is proposed that specific limits on water and sediment be added to the regulations, to supplement the existing visual tests for colour and appearance. This will bring New Zealand into line with international specifications. Specifications for water and sediment are already included in the NZRC and Refinery Users specification so this will lock current good practice into the regulations. The limits and test methods proposed align with World-Wide Fuel Charter and current European specifications.
New Regulations Proposed
| Current Regulations | Proposed changes |
|---|
| Water Content: not currently regulated | Immediate introduction of water content test: 200 mg/kg maximum (test method to be determined) |
| Total Contamination: not currently regulated | Immediate introduction of total contamination test: 24 mg/kg maximum (test method ASTM D 2276) |
8.2.4 Lubricity
As noted in Section 8.1.7, removal of sulphur from diesel can reduce its natural lubricity, causing increased wear in fuel pumps and other engine components. This problem was first identified when ULSD was first introduced in Sweden, but adequate lubricity levels can be achieved through the use of suitable additives. Lubricity tests are now commonly being included in many diesel specifications elsewhere.
Lubricity is not easily measured in a laboratory. The High Frequency Reciprocating Rig (HFRR) test uses a laboratory rig to measure the effective wear than can be expected on fuel pump parts. This is measured as a wear scar diameter in microns (µm). The proposed specification is a maximum wear scar diameter of 460 µm (microns) at 60°C, measured in accordance with test procedure IP450.
In view of future reductions in the sulphur content of New Zealand diesel (both in the longer term as well as in the longer term), and the availability of LSD on the market already, it is proposed that the lubricity test apply to all diesel, irrespective of sulphur content. However, if a higher sulphur marine grade of diesel again becomes available, it may be appropriate to consider an exemption.
New Regulations Proposed
| Current Regulations | Proposed changes |
|---|
| Lubricity: not currently regulated | Immediate introduction of a lubricity test:
HFRR wear scar diameter at 60°C - 460 microns maximum (test method IP 450) |
8.2.5 Filter Blocking Tendency
The Filter Blocking Test measures the filterability of diesel and is proposed in response to the recent problems encountered with diesel fuel dosed with a cold flow improver. The test measures a volume of a sample through a 1.6 micron (µm) filter and records the increase in pressure drop as the sample is filtered. Given the potential operating problems that poor filterability can cause in diesel engines, this requirement is being included to provide additional protection for the consumer.
The proposed test method is IP 387, with a specified maximum value of 1.41 (a dimensionless value called the filter blocking tendency). The test is already used in most refineries in Australia.
New Regulations Proposed
| Current Regulations | Proposed changes |
|---|
| Filter Blocking Tendency: not currently regulated | Immediate introduction of a filter blocking test: 1.41 maximum (test by IP 387) |
8.2.6 Conductivity
Diesel that is low in sulphur may also have a lower electrical conductivity. Insufficient conductivity is a safety issue because it can lead to a build-up of static charge during transfer (such as when filling bulk storage tanks or road tankers). Conductivity is generally not an issue for vehicle fuel tanks because of the low velocity of fuel through pump nozzles. This is primarily an operating consideration for the oil industry and it can be corrected with conductivity improving additives. There is no proposal to regulate at this stage.
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