A series of tests was conducted on a Toyota, four-cylinder, spark ignition engine which was modified to run on either gasoline or natural gas. The aim of the experiment was to investigate the performance and combustion behavior of natural gas, with particular emphasis on its low burning velocity. A pressure transducer installed in the cylinder head was used to obtain pressure versus crank angle curves from which mass burn rates and burning velocities were calculated, using a heat release analysis program. Results indicate that the low laminar burning velocity of natural gas extends its ignition delay period (time to 1 percent burned) by up to 100 percent compared with gasoline. This contrasts with the remainder of the combustion period which is dominated by turbulence effects that produce very similar burning velocities for the two fuels.

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