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Cover of A literatyre revuew based assessment on the impacts of a 20% ethanol gasoline fuel blend on the australian vehichle fleet

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A Literature Review Based Assessment on the Impacts of a 20% Ethanol Gasoline Fuel Blend on the Australian Vehicle Fleet

Environment Australia, November 2002


About this literature review

This report represents part of the work commissioned by Environment Australia (EA) under tender 34/2002 'Environment Australia Project: 'Market Barriers to the Uptake of Biofuels - Testing Petrol Containing 20% Ethanol (E20)''. Specifically, this report satisfies the section of work Section titled 'Analysis of Impacts'.

A study has been conducted on the suitability of ethanol/gasoline blend fuels that contain greater than 10% (by volume) ethanol. The study has focused on researching effect of high ethanol blend fuels on noxious and greenhouse emissions, vehicle operability and engine and fuel system durability. The study needs to be considered in the context of the current vehicle fleet, which must operate effectively and efficiently on the 20% ethanol blend without re-tuning/recalibration or other modification. In many cases, there is insufficient or conflicting information available, indicating the detailed testing program, which is to be undertaken as part of tender 34/2002, is warranted.

The addition of ethanol increases the available oxygen for combustion. Older vehicles with open-loop fuel systems suffer enleanment of the combusted mixture. The net effect on legislated emissions would be a reduction in carbon-monoxide (CO) emissions. The effect on unburnt hydrocarbon (HC) and oxides of nitrogen (NOx) emissions is more complex, and is dependent on the engine calibration.

Vehicles fitted with closed loop fuel systems and three-way catalyst (TWC) systems show reduced CO emissions, and generally reduced total HC emissions with an ethanol content beyond 20%. Tailpipe NOx emissions increased by approximately 30% with a 20% ethanol blend compared with no increase for a 10% blend. The 30% increase in NOx corresponds to approximately 10 to 15% of the current Australian NOx emissions regulation for passenger vehicles, but could be as much as 50% of the new proposed emissions regulation (ADR 79/00).

The available data on unregulated emissions for ethanol blends greater than 10% is small. Aldehyde emissions will increase as the percentage of ethanol increases. Predominantly, this is due to acetaldehydes increasing by more than 100% with ethanol blends of 10%. Formaldehyde emissions will remain relatively constant. Other unregulated emissions of toxic and greenhouse gases are unlikely to change.

Carbon dioxide (CO2) emissions reductions for 20% ethanol blends are reported to be small and may not be significant when considering the total fuel cycle. The ethanol production process may dominate any small reductions in vehicle tailpipe levels. In the case of vehicle fuel economy, this may fall by approximately 7% for a 20% ethanol blend. This loss is primarily due to the reduction in energy content of the 20% blend.

Evaporative emissions are likely to increase with higher blends of ethanol, with increasing evaporative emissions measured during vehicle 'hot soak' testing. Future Australian emissions legislation will include a further 'real time diurnal test' which is highly likely to exacerbate the problem. The E20 blend may increase evaporative emissions by vapour permeating through some fuel system plastics.

Vehicle operability may deteriorate with 20% ethanol blends. Those vehicles fitted with lean calibrated carburettors are likely to display the most significant deterioration across the driveability spectrum due to enleanment. For those vehicles fitted with closed loop fuel injection systems, enleanment is likely to deteriorate the cold start performance and warm up. However this is likely to be dependent on the ability of the engines control system to maintain stoichiometry, a function related to the manufactures control strategy. In terms of hot weather driveability, the newer vehicle fleet should be more robust though this is most dependent on the design of the fuel system.

The anti-knock capability of high ethanol blends is not as simple as defined by the standard measurements of Research and Motor Octane Numbers, (RON &MON). Testing suggests that there is either a negative or at best a marginal benefit with ethanol blends beyond 5% by volume. It is likely that high engine speed knock will occur due to the increase in octane sensitivity of the 20% ethanol blend. Vehicles fitted with knock sensors will not exhibit the associated 'pinging' sound, though depending on the reduction in spark advance may suffer reduced acceleration performance.

The impact of a 20% ethanol blend on engine and fuel system durability of the Australian vehicle fleet is unclear. In terms of engine wear the literature reviewed is vague, leaving the only valid conclusion that testing is required to obtain data to form a view. The literature studied indicates that there is a significant potential problem for those vehicles with fuel systems that have reached the 'normal' stabilised level of internal deposits, which are passive to gasoline. Upon introducing these vehicles to a 20% ethanol blend, these deposits are likely be stripped away causing fuel filter blockages and plugging of fuel metering components.

Perishing and swelling of elastomeric and plastic materials making up the fuel system is highly likely on the older vehicle fleet when exposed to E20. The newer fleet may be less likely to show these problems as many of the components are globally sourced and therefore may be compatible with up to 10% ethanol blends providing some element of protection for an E20 blend. Whenever there is any potential for a fuel leak, a potentially hazardous situation is created.

The potential for corrosion of the metal components of the fuel system has also been identified by this literature study. Metal surfaces within the fuel system must be specifically treated to guard against corrosion with the E20 blend. This is likely to be a longer term issue as the corrosion process is relatively slow, however the potential for a fuel leak is clear.

It is expected that the issues and shortcomings in information for E20 blends identified in this report will be appropriately addressed and reported in due coarse by the execution of the scope of work provided within the Orbital Engine Company tender 34/2002. This is assuming that the 80,000km vehicle mileage accumulation is undertaken as part of the EA Project.