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Models for the convective heat transfer from the combustion gases to the walls inside a spark ignition engine are an important keystone in the simulation tools which are being developed to aid engine optimization. The existing models have, however, been cited to be inaccurate for hydrogen, one of the alternative fuels currently investigated. One possible explanation for this inaccuracy is that the models do not adequately capture the effect of the gas properties. These have never been varied in a wide range because air and ‘classical’ fossil fuels have similar values, but they are significantly different in the case of hydrogen. As a first step towards a fuel independent heat transfer model, we have investigated the effect of the gas properties on the heat flux in a spark ignition engine.

The use of methanol as spark-ignition engine fuel can help to increase energy security and offers the prospect of carbon neutral transport. Methanol's properties enable considerable improvements in engine performance, efficiency and CO2 emissions compared to gasoline operation. SAE paper 2012-01-1283 showed that both flex-fuel and dedicated methanol engines can benefit from an operating strategy employing exhaust gas recirculation (EGR) to control the load while leaving the throttle wide open (WOT). Compared to throttled stoichiometric operation, this reduces pumping work, cooling losses, dissociation and engine-out NOx. The current paper presents follow-up work to determine to what extent these advantages still stand over an entire drive cycle. The average vehicle efficiency, overall CO2 and NOx emissions from a flexible fuel vehicle completing a drive cycle on gasoline and methanol were evaluated.

The use of light alcohols as SI engine fuels can help to increase energy security and offer the prospect of carbon neutral transport. These fuels enable improvements in engine performance and efficiency as several investigations have demonstrated. Further improvements in efficiency can be expected when switching from throttled stoichiometric operation to strategies using mixture richness or exhaust gas recirculation (EGR) to control load while maintaining wide open throttle (WOT). In this work the viability of throttleless load control using EGR (WOT EGR) or mixture richness (WOT lean burn) as operating strategies for methanol engines was experimentally verified. Experiments performed on a single-cylinder engine confirmed that the EGR dilution and lean burn limit of methanol are significantly higher than for gasoline. On methanol, both alternative load control strategies enable relative indicated efficiency improvements of about 5% compared to throttled stoichiometric operation.

Stricter CO2 and emissions regulations are pushing spark ignition engines more and more towards downsizing, enabled through direct injection and turbocharging. The advantages which come with direct injection, such as increased charge density and an elevated knock resistance, are even more pronounced when using low carbon number alcohols instead of gasoline. This is mainly due to the higher heat of vaporization and the lower air-to-fuel ratio of light alcohols such as methanol, ethanol and butanol. These alcohols are also attractive alternatives to gasoline because they can be produced from renewable resources. Because they are liquid, they can be easily stored in a vehicle. In this respect, the performance and engine-out emissions (NOx, CO, HC and PM) of methanol, ethanol and butanol were examined on a 4 cylinder 2.4 DI production engine and are compared with those on neat gasoline.

Methanol is a promising fuel for future spark-ignition engines. Its properties enable increased engine efficiency. Moreover, the ease with which methanol can be reformed, using waste exhaust heat, potentially offers a pathway to even higher efficiencies. The primary objective of this study was to build and validate a model for a methanol fueled direct-injection spark-ignition engine with on-board fuel reforming for future investigation and optimization. The second objective was to understand the combustion characteristics, energy losses and engine efficiency. The base engine model was developed and calibrated before adding a reformed-exhaust gas recirculation system (R-EGR). A newly developed laminar burning velocity correlation with universal dilution term was implemented into the model to predict the laminar burning velocity with the presence of hydrogen in the reforming products.