Predictions and measurements of spark-ignition engine characteristics using ammonia and other fuels
The project reported here involves the development of a computer model for determining the characteristics of a spark-ignition engine. The model incorporates detailed consideration of the combustion process -and includes calculations for heat transfer between the contents of the engine combustion chamber and the containing surfaces. Composition changes are taken account of by considering thermodynamic equilibrium of the chemical species that might be present during the combustion and expansion processes. In the case of ammonia, the equilibrium composition is also considered during the compression process. The model has been used to predict the performance of an engine using the following fuels: gasoline (represented by iso-octane in the model), methanol, propane and ammonia. These provide a wide range of properties, air fuel ratios for complete combustion and combustion characteristics so as to give an increased range for testing the validity of the model. Calculations have been performed for a wide ranges of compression ratio and air-fuel ratio for each fuel. Measurements have been made, using the same fuels, in a single cylinder Ricardo E6 engine fitted with a spark ignition cylinder head and fuel supply and metering systems suitable for the four fuels. For a constant speed of 2000 r/min the compression ratio was varied over its appropriate range for each fuel. For each compression ratio the air fuel ratio was varied. Measurements included speed, compression ratio, fuel and air flow rates, dynamometer load, and exhaust gas composition. (carbon dioxide, carbon monoxide, oxides of nitrogen, oxygen, and hydrocarbons). All measurements were for optimised spark timing. The results are compared with predictions and with published work.