A Study of Alcohol Blended Fuels in an Unthrottled Single Cylinder Spark Ignition Engine

Abstract

This work involved study of the effects of alcohol blends on combustion, fuel economy and emissions in a single cylinder research engine equipped with a mechanical fully variable valvetrain on the inlet and variable valve timing on the exhaust. A number of splash blends of gasoline, iso-octane, ethanol and butanol were examined during port fuel injected early inlet valve closing operation, both with and without variable valve timing. Under low valve overlap conditions, it was apparent that the inlet valve durations/lifts required for full unthrottled operation were remarkably similar for the wide range of blends studied. However, with high valve overlap differences in burning velocities and internal EGR tolerances warranted changes in these valve settings. In turn, it was concluded that high ethanol content blends facilitated minimum throttling at the inlet valve itself and the largest relative savings in terms of fuel consumption, engine-out emissions of NOx and (corrected) unburned hydrocarbons.

Control-oriented modelling of combustion phasing for a fuel-flexible spark-ignited engine with variable valve timing

“…Ethanol is an attractive option for offsetting dependence on petroleum based fuels; however, the differences in fuel properties between gasoline and ethanol (as summarized in Table 1) can significantly alter engine performance. 1–4 Due to the oxygen content of ethanol, the stoichiometric air–fuel ratio (AFR) of ethanol is substantially different to gasoline. As a result, the air and fuel controllers must target different values for ethanol blends.…”

“…In steady state, these look-up tables provide a spark timing that ensures that the combustion timing (CA50) occurs at its optimal timing. However, if the same look-up tables for ignition control are used for gasoline, ethanol and gasoline–ethanol blends, engine performance will be suboptimal when running any blend fraction of ethanol, 1,4 and therefore, it is essential to take fuel type into consideration when dictating desired set points. One method of achieving this is by adding additional look-up tables to be used for different fuel blends; however, since fuel-flexible spark-ignition (SI) engines commonly run blends of gasoline and ethanol of up to 85% ethanol, adding look-up tables for all possible fuel blends would be quite intensive.…”