Although compressed natural gas (CNG) is considered one of the most promising alternative fuels for spark-ignition engines, there are still uncertainties about it''s combustion and exhaust emission characteristics that require further investigation. In this study, the flow and combustion in a purpose-built, single-cylinder optical spark-ignition engine fuelled with CNG and equipped with a four-value cylinder head were examined using LDV, PIV, flame imaging and a sampling probe incorporated into the spark plug for measuring the local hydrocarbon levels at the time of ignition. Modification of the inlet ports using sleeves and injection of CNG against open rather than closed valves allowed stronger tumble, with increase turbulence levels near the spark plug, and charge stratification at the time of ignition which resulted in faster flame propagation and reduced cycle-to-cycle variations, thus approaching the combustion performance of gasoline-fuelled engines but with potential for reduced NOx emissions as a result of the extension of the engine''s lean limit.
Flow and Combustion Characteristics in a Four-Valve Spark-Ignition Engine Fuelled By CNG
1999
Aufsatz (Konferenz)
Englisch
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