The potential of methanol as a fuel for flex-fuel and dedicated spark-ignition engines

Using light alcohols in spark-ignition engines can improve energy security and offers the prospect of carbon neutral transport. The properties of these fuels enable considerable improvements in engine performance and pollutant emissions. Whereas most experimental studies have focused on ethanol, this paper provides experimental results gathered on various methanol-fuelled engines. A comparison against gasoline on two flex-fuel engines yielded relative efficiency benefits of about 10% for methanol thanks to more isochoric combustion, less pumping, cooling and dissociation losses. Lower combustion temperatures allowed to reduce engine-out NOx by 5–10 g/kWh. The CO2 values dropped by more than 10%. Alternative load control strategies, employing mixture richness or exhaust gas recirculation (EGR) to control load while keeping the throttle wide open, were compared on a single cylinder engine. The EGR strategy seems preferable as it allows to increase part load efficiency up to 5% without sacrificing in terms of tailpipe emissions. Finally, this load control strategy of choice was applied to a turbocharged, high compression ratio engine to demonstrate that methanol can be used in dedicated engines with diesel-like efficiencies (up to 42%) and emission levels comparable to or lower than gasoline engines.