Performance and emissions of a SI engine using methanol-water blends

Using liquid alcohols, such as methanol and ethanol, in spark-ignition engines is a promising approach to decarbonise transport and secure domestic energy supply. Methanol and ethanol are compatible with the existing fuelling and distribution infrastructure and are easily stored in a vehicle. They can be used in internal combustion engines with only minor adjustments and have the potential to increase the efficiency and decrease noxious emissions compared to gasoline engines. In addition, methanol can be synthesized from a wide variety of sources, including renewably produced hydrogen in combination with atmospheric CO2. Presently, during the production of ethanol or methanol a dehydration step is always applied. This step accounts for a significant part of the entire production process' energy consumption and thus, from an economical point of view, methanol and ethanol could become more interesting alternative fuels if the costs related with dehydration could be reduced. Also, methanol and ethanol are prone to absorb water when they are exposed to the atmosphere for a considerable amount of time, for example during transport or storage. The present study gives insights into the advantages that could exist with methanol-water blends and compares the brake thermal efficiencies and engine-out emissions from a production-type four-cylinder SI gasoline engine running on gasoline, pure methanol and methanol-water blends. Methanol-water blends of 2.5% v/v, 5% v/v and 10% v/v water are tested. It is shown that the brake thermal efficiency does not differ significantly for all methanol fuels and is still higher than the efficiency on gasoline. NOx emissions are reduced substantially for the fuels with higher water content