1990-08-01

Comparison of Temperatures Measured in Natural Gas and Gasoline Fuelled Engines 901503

There has been concern that the use of natural gas in engines designed for gasoline fuelling can give rise to excessive temperatures. This is based on experience of exhaust valve recession, high piston temperatures and hot exhaust systems with conversions in New Zealand.
In order to establish some data this work has measured exhaust gas temperatures, piston, exhaust valve and cylinder head temperatures in a single cylinder research engine.
The data show that at wide open throttle and with the engine tuned to similar operating conditions (ie. the same fuel-air ratio and MBT spark timing), the natural gas fuelled engine generally has lower surface temperatures within the combustion chamber and lower exhaust gas temperatures than the gasoline fuelled engine. When the engine is operated at the same load on the two fuels the combustion chamber temperatures were similar for the two fuels.
The measurements also show that temperatures are very sensitve to fuel-air ratio and spark timing which leads to the conclusion that on-road experience of high temperatures with natural gas fuelling are probably the result of these factors, not of the fuel itself.

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