Effects of hydrogen admixture on efficiency and emissions in a spark-ignition engine fueled with gasoline and methanol

There is increasing regulatory and public pressure to reduce greenhouse gas emissions from the transport sector. This can be achieved by further improving the efficiency of internal combustion engines. The addition of small amounts of hydrogen to the combustion process of a spark-ignition engine can reduce CO₂ emissions by reducing the carbon content of the fuel as well as increasing engine efficiency. Therefore, the combination of hydrogen port injection with direct injection of a liquid fuel was investigated on a single-cylinder research engine. RON95 E10 gasoline and methanol were tested as liquid fuels. The measurements carried out show that the addition of hydrogen reduces the knocking tendency of RON95 E10 gasoline, allowing a more efficient combustion phasing. Hydrogen admixture also increases the tolerance to mixture dilution, allowing an increase in the relative air-fuel ratio of 0.8 and thus further efficiency gains. The maximum net indicated efficiency achieved with RON95 improved by 4.9%-pts. With methanol as a liquid fuel, there is no advantage of hydrogen admixture in the combustion phasing due to the high knock resistance of methanol. Hydrogen admixture still allows leaner operation by 0.35 units of relative air-fuel ratio, but does not result in increased efficiency. The maximum indicated efficiency with hydrogen admixture was 1.5%-pts. lower than with pure methanol.