Petrol Properties and Changes Proposed
Octane Number
Octane number tells us about petrol's resistance to abnormal or uncontrolled combustion. The most common symptom of uncontrolled combustion is detonation or "knock", caused by the spontaneous combustion of a portion of unburnt air-fuel mixture.
Knock can occur when using fuel with too low an octane rating for the engine, and severe knocking can cause engine damage. The higher the octane number of a petrol, the greater its resistance to knocking.
Using fuel of higher octane than required does not affect engine performance - it just costs more.
Our petrol grades are given two measures of octane rating:
- RON (Research Octane Number) is an indicator of petrol's anti-knock performance at lower engine speed and typical acceleration conditions. Petrol is commonly referred to by its RON - e.g., 91 regular or 96 premium have RONs of 91 and 96 respectively.
- MON (Motor Octane Number) is an indicator of the anti-knock performance of fuel under higher engine speed and higher load conditions.
Every engine is designed to operate to best performance using a certain octane rating. Many Japanese cars, for example, are designed to run on 90 RON. Newer engine technologies that are being developed to achieve greater fuel economy require higher-octane petrol. European studies suggest a 95 RON/85 MON grade is the optimum octane rating. This measure provides a balance between reducing fuel consumption, by improving fuel performance, and minimising the extra energy required to produce the higher octane fuel.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
Octane number for regular grade petrol:
91 minimum RON; 82 minimum MON | no change |
Octane number for premium grade petrol:
95 minimum RON; 85 minimum MON | no change |
Colour
Petrol can be coloured through the addition of dyes. Currently, the Regulations require that petrol must be coloured so that it cannot be mistaken for a harmless substance. The intention is to reduce the risk of petrol being swallowed because it was mistaken for water or another drink.
In practice, petrol colour can assist with distribution by helping to prevent the wrong octane petrol being added to the wrong storage tank. Currently, there is no requirement that all retailers use the same colour to distinguish petrol, and different colours are used for premium and regular petrol. Regulating colour does not seem to be achieving the original intention. Therefore, it is proposed that this requirement be deleted from the Regulations.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Colour: not to be mistaken for a harmless substance | Immediate removal of requirement |
Volatility and Distillation Parameters
Volatility - the tendency of petrol to vaporise - is critical to engine performance. Petrol must vaporise readily to allow easy starting and driveability when an engine is cold, but not so much that it begins to evaporate in fuel lines when the engine is hot (this is known as vapour lock and impedes fuel flow). Volatility also affects vapour emissions. For environmental and health reasons, the fuel must not be so volatile that evaporation from the fuel tank is excessive in warm weather.
Four main measures of volatility commonly used are:
E70, E100, E150 and E180 are measures of the proportion of petrol, by volume, that evaporates when it is heated to 70°C, 100°C, 150°C and 180°C respectively. E70 is a measure of cold running performance.
Distillation end point is the temperature by which all the volatile components of petrol have boiled off.
Reid Vapour Pressure (RVP) is a direct measure of volatility at ambient temperatures.
Flexible Volatility Index (FVI) is a parameter calculated from the RVP and the measured value of E70 and is an indication of hot running performance (the tendency for vapour lock).
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| E70: 25% minimum; 45% maximum | Immediate reduction of minimum E70 to 22% |
| E100: 45% minimum; 67% maximum | no change |
| E180: 90% maximum | Stage 1 replacement of E180 specification with E150, set at 75% maximum |
| Distillation end point: 220°C maximum | Stage 1 reduction of distillation end point to 215°C
Stage 2 further reduction of distillation end point to 210°C |
| Reid Vapour Pressure: not currently specified | Immediate introduction of maximum RVP limits by season, to apply to all petrol (see table below) (test method ASTM D 323)
Stage 1 reduction of RVP limits
Stage 2 further reduction of RVP limits |
| Flexible Volatility Index: 77.5 minimum; 115 maximum | Immediate removal of minimum limit on FVI |
Proposed RVP Limits by Season
| Season | Dates | Immediate | Stage 1 | Stage 2 |
| Summer: | 1 December - 30 April | 85 kPa max | 75 kPa max | 65 kPa max |
| Autumn: | 1 May - 31 May | 90 kPa max | 85 kPa max | 80 kPa max |
| Winter: | 1 June - 30 September | 95 kPa max | No further change | No further change |
| Spring: | 1 October - 30 November | 90 kPa max | 85 kPa max | 80 kPa max |
The existing E70 minimum value was increased from 15% to 25% in 1994, after cold starting problems were encountered with a shipment of imported fuel. Comparable international requirements for cold climates are 22%. Reducing the E70 minimum to 22% by volume will still allow for good cold starting and be less constraining on refineries.
Specifying an E150 value instead of E180 will align with the European standard and provide better control of volatility.
Reducing the distillation end point to 210°C will align with the current European standard and the Australian standard for 2005 and will reduce smoke emissions (due to reduced high molecular weight aromatics). The Marsden Point Refinery should not have any difficulty in meeting this requirement. Australian refineries, from where New Zealand sources some of its imported petrol, are not required to meet this requirement until 2005, so it would be advantageous to time any change to coincide with Australia's initiatives.
For environmental reasons, many countries specify RVP limits to reduce evaporation losses from vehicles and during bulk storage and distribution of petrol. Lower RVP affects refining operations by reducing the total petrol yield from crude oil. This increases overall production costs. Immediate changes proposed will maintain RVP levels currently supplied in New Zealand. The dates of the proposed RVP seasons have been adjusted from industry practice so they are applicable at the pump, rather than at the point of production or distribution. The subsequent staged changes are designed to provide adequate lead times for the Marsden Point Refinery and suppliers of imported petrol to meet the new requirements.
Engines with carburettors are more susceptible to vapour lock than those with fuel injection systems. A maximum FVI limit avoids this vapour lock problem. As carburettor engines currently make up a significant proportion of the New Zealand fleet, the maximum limit on FVI needs to be retained. The minimum requirement is not seen as necessary to control vapour lock or other engine performance criteria and is proposed to be deleted.
The suggested changes to volatility and distillation parameters will reduce smoke, particulate and evaporative emissions without affecting engine performance.
Residue and Existent Gum
Residues and gums are essentially what is left of a fuel after all the volatile components are boiled off. The residual waxes and gums may form deposits in engine components, which can affect vehicle performance and emissions.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Residue: 2% maximum by volume of petrol | no change |
| Existent gum (solvent washed): 5mg/100ml maximum | no change |
Corrosiveness
Corrosiveness in petrol is usually a result of free sulphur or sulphur compounds combining with water from combustion to form acids. Corrosion can affect engine components, fuel tanks and dispenser pumps and may cause deposits to form.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Copper strip corrosion test: 100°C for 2 hours, then compare with a reference sample | Immediate: Copper strip corrosion test: 50°C for 3 hours, then compare with a reference sample |
The test for corrosiveness involves immersing a strip of polished copper in a sample of the petrol, heating it for a specified length of time, and then comparing it with a reference sample. The proposed change will align with international practice and will offer an adequate corrosion protection test that is less hazardous to the technician.
Sulphur
Sulphur occurs naturally in crude oils. It must be removed to an acceptable level during the refining process as it causes corrosion and reduces the efficiency of catalytic converters (used to control vehicle emissions). New petrol engine technologies aimed at improving fuel economy and achieving lower emissions, such as gasoline direct injection, require low sulphur levels.
The current European requirement is 150 parts per million (ppm) maximum sulphur in petrol, with 50 ppm maximum sulphur required by 2005. Petrol containing 10 ppm maximum sulphur is expected to be available in Europe by 2011.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Sulphur: 500 ppm maximum (mg/kg) | Immediate reduction of maximum to 150 ppm (test method ASTM D 5453)
Stage 2 further reduction to 50 ppm maximum
Ultimate requirement for sulphur free petrol (less than 10 ppm) |
While the current Regulations specify a maximum of 500 ppm sulphur, petrol supplied from the Marsden Point Refinery is well below 150 ppm, as is much of our imported petrol. The change to a maximum of 150 ppm sulphur will therefore maintain the low sulphur level petrol New Zealand has been using. If this is not regulated, there is a possibility sulphur levels could rise as suppliers source higher sulphur blendstocks and imported petrol in response to other proposed changes to the Regulations.
Marsden Point Refinery can already produce petrol with a maximum of 50 ppm sulphur. However, not all refineries in the Asia-Pacific region currently have the capacity to produce low sulphur petrol. Adopting a transitional level of 150 ppm should not present a barrier to improvements in vehicle technology in the immediate future. Further reductions will bring New Zealand into line with European specifications proposed for 2005.
Oxidation Stability
Oxidation stability is a measure of the stability or shelf life of petrol during storage. Oxidation occurs when components in the petrol react over time with oxygen in the air, resulting in the formation of gums, deposits and sludges in fuel systems and engine components.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Oxidation stability induction period:240 minutes | Immediate: Oxidation stability induction period of 360 minutes |
Oxidation stability is measured by heating a sample of fuel in a sealed vessel with oxygen and measuring the time it takes to absorb the oxygen (i.e., oxidise) and form gum. The measured time is called the induction period. Increasing the induction period to 360 minutes will regulate the current good practice levels achieved in New Zealand and will align with international practice for the test.
Lead
New Zealand has used lead-free petrol since 1996. Previously, lead was added to petrol to improve its octane rating. The use of lead is restricted because of its detrimental effects on health. The current regulation was set to allow for a small level of lead contamination in distribution and retailing systems.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Lead: 13 mg per litre maximum | Immediate reduction to 5 mg per litre maximum |
The proposed change will reduce the contamination level allowance and align with international practice.
Total Aromatics
Aromatics are molecules containing carbon and hydrogen with a simple benzene ring structure. Aromatics occur naturally in crude oil and can also be produced in some refining processes. Aromatics common in petrol include benzene (specifically discussed below), toluene and xylene.
Controlling the level of aromatics directly limits evaporative losses and exhaust emissions of these compounds, thereby reducing human exposure to them. Many countries have moved in recent years to regulate the amount of aromatics in petrol in order to achieve public health and air quality benefits.
Sudden large changes in aromatics levels can cause loss of elasticity or shrinkage in some elastomers, the synthetic rubber-type materials frequently used in vehicle fuel systems. Older vehicles tend to be more susceptible to this problem.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Total Aromatic Compounds: 48% maximum by volume (including benzene) | For regular grade: Immediate reduction to 40% maximum by volume
For premium grade: Stage 2 reduction to 42% maximum by volume |
Regular grade accounts for around 75% of total New Zealand petrol consumption and aromatics levels in regular grade are already much lower than in premium. The immediate change for regular grade will maintain these lower levels.
Aromatics are high octane constituents of petrol. The proposed limits on benzene (see below) and on the octane enhancing additives MTBE (see Oxygenates) and MMT (see Manganese) will make the early reduction of other aromatics in premium petrol difficult. Therefore, for premium grade, a reduction down to 42% by volume maximum in Stage 2 is proposed.
Benzene
Benzene is the simplest type of aromatic (see above) occurring naturally in crude oil and is also produced in some refinery processes. Benzene is a known carcinogen. Vehicles emit benzene through evaporation from their fuel systems and through their exhausts. International practice in recent years has been to lower limits on benzene in response to health and air quality concerns.
Annual average concentrations of benzene in the air in most of our cities are within proposed national air quality guidelines, although these guidelines are exceeded in some places adjacent to major roads. However, many New Zealand cities are unlikely to meet the stricter guidelines for benzene proposed for 2010.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Benzene: 5% maximum by mass (equivalent to around 4.2% maximum by volume) | Immediate change to specifying benzene content as % by volume; set at 4% maximum
Stage 1 reduction to 3% maximum by volume
Stage 2 reduction to 1% maximum by volume |
The immediate change will align with international practice by specifying benzene limits as a percentage volume.
Benzene is a useful source of octane. Reducing allowable benzene levels will mean other high-octane constituents or additives will need to be used. However, reducing the benzene content of petrol is seen as a priority over reduction of other aromatic compounds such as toluene and xylene, which have lesser health effects but are also good sources of octane.
A staged reduction to 1% is proposed to align with Australia. This timetable recognises that refineries in the Asia-Pacific region are not all able to meet the 3% and 1% benzene limits. The Marsden Point Refinery will require capital investment with a 3-5 year lead time to meet the 1% limit. Estimates based on overseas figures indicate that it could cost about $NZ25-35 million.
Oxygenates
Oxygenates are organic compounds containing carbon, oxygen and hydrogen. They are added to petrol as a blending component and to increase octane. They improve combustion and reduce carbon monoxide formation and hydrocarbon emissions. Oxygenates include alcohols (e.g., ethanol, methanol) and ethers (e.g., MTBE - methyl tertiary-butyl ether). Some oxygenates such as ethanol can increase fuel volatility if blended in high concentrations and others, such as methanol, can be corrosive. Unlike petrol, all oxygenates are readily soluble in water. The current Regulations effectively ban the use of oxygenates, other than MTBE.
Changes Proposed to the Regulations
| Current Regulations | Proposed changes |
|---|
| Oxygenates: 0.1% maximum by mass on total oxygenates, excluding MTBE | Immediate: 0.1% maximum by mass applies to all petrol. Changes to ethanol and MTBE as below |
| MTBE: Up to 11% by volume | Immediate limit of 1% maximum by volume, applying to all petrol |
| Ethanol: limited as per total oxygenates | Immediate: Allow addition of ethanol to petrol up to 10% by volume, subject to a testing and approval process |
The Regulations currently require only petrol sold by retail sale to meet the specified limit. It is proposed the restrictions on MTBE and other oxygenates (other than ethanol) apply to all petrol.
MTBE
Petrol sold in New Zealand does not generally contain MTBE, although the current Regulations allow up to 11% by volume.
MTBE mixes readily with water, and in the USA leakage from storage tanks has tainted groundwater, imparting an unpleasant taste and smell even at very low concentrations. While MTBE has been widely used internationally for many years, a number of jurisdictions propose to ban it in the near future. Its use has been the subject of much debate in Australia.
It is proposed that New Zealand adopt a precautionary approach and restrict the use of MTBE and other ethers until they are shown to be safe with regard to the environment and public health. A 1% limit for MTBE will allow for contamination levels that can result when MTBE-containing residue from previous cargoes is mixed with MTBE-free petrol in petrol importing ships.
Ethanol
Ethanol is an alcohol that can be produced through the fermentation of biological material such as sugar cane, corn, and whey. It is the alcohol found in wine and other alcoholic beverages.
Ethanol is used as a blending component of petrol in some countries, for example in parts of the United States and Australia. Generally, 10% ethanol by volume is the amount blended into automotive petrol. As an oxygenate, it reduces some air contaminants in vehicle exhaust emissions. Because ethanol is produced from a renewable resource, its use as a blending component reduces the consumption of fossil fuels in vehicles, thereby reducing vehicle emissions of greenhouse gases.
There are potential drawbacks to using ethanol-blended petrol. In some vehicles, ethanol in petrol can cause elastomers, the rubber-type material in fuel systems, to swell and lose strength. This problem is similar to the one encountered with high levels of aromatics (see Total Aromatics). Older vehicles tend to be more susceptible to this problem, as newer vehicles worldwide have been manufactured to allow the use of ethanol blends.
Ethanol may cause poor vehicle performance, including cold starting and cold weather driveability problems, especially in older vehicles with carburettors. Mixing ethanol-blended petrol and unblended petrol in the same fuel tank may cause rough running and other driveability problems.
During the 1980s there was some government research on using ethanol-blended petrol. This research was not progressed for various reasons, including difficulties in sourcing reliable long-term supplies of ethanol. Recently, some interest has been expressed in the possibility of supplying ethanol-blended petrol to the New Zealand market.
Given that the use of ethanol-blended petrol could assist New Zealand to meet climate change responsibilities to reduce greenhouse gas emissions, there is merit in providing for the possibility of petrol blended with up to 10% ethanol. However, the potential risks of ethanol-blended petrol need to be carefully managed.
To achieve both of these objectives, one approach would be to allow the sale of ethanol-blended petrol for a limited amount of time on a test basis. A decision on the sale of ethanol-blended petrol on a permanent basis could then be based on the outcome of the New Zealand-based trial. There would need to be a clear framework for this testing and approvals process. A test period of 6 to 12 months would probably be needed. The test would need to demonstrate clearly that it had involved a large number and range of vehicles and that no adverse effects on engine performance had occurred. Consumers taking part in the test would need to be fully informed and to agree to their participation. It should be noted that such an approach may require an amendment to the legislation under which the Regulations are made.
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