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An experimental study was undertaken to investigate burn characteristics of homogeneous charge natural gas fueled, single cylinder, spark ignition engine. The engine was instrumented with flame detection sensors, pressure transducer, a wide-range exhaust oxygen sensor and several other devices to measure parameters associated with charge and combustion. The pressure data was used in a model to estimate mass of charge burned during the combustion events. Engine compression ratio was varied within a small range. The flame kernel development time was influenced by mixture stoichiometry, engine load and speed. Very lean equivalence ratio had pronounced effect on kernel development. The combination of light load and very lean air-to-fuel ratio provided less favorable environment for the formation of stable flame kernel. An increase in compression ratio helped to shorten flame development time.

An experimental study was conducted to determine potential of natural gas in lowering exhaust emissions from small spark ignition engines. A single cylinder, four-stroke, air-cooled spark ignition engine was used in the study. The investigation showed that increasing engine compression ratio from 8:1 to 10:1 reduced penalty in power normally associated with natural gas engine. The engine was able to run very stable at equivalence ratio as lean as 0.65 while the same engine could not be run at equivalence ratio below 0.85 on gasoline. Best thermal efficiency and reduced emissions of hydrocarbons and oxides of nitrogen were realized around equivalence ratio 0.75. Reducing equivalence ratio further lowered emissions of oxides of nitrogen significantly while increase in hydrocarbons was small. Most of the hydrocarbons in exhaust were of the methane type which have low ozone forming reactivity.