Comparison of Emissions from Natural Gas and Gasoline Fuelled Engines - Total Hydrocarbon and Methane Emissions and Exhaust Gas Recirculation Effects

This work investigated the characteristics of both total and methane hydrocarbon emissions from a spark-ignition research engine fuelled with natural gas and gasoline. The engine was operated at a range of equivalence ratios, spark timings and speeds. Measurements were also made during warm-up. The effects of exhaust gas recirculation at stoichiometric operation with special regard to oxides of nitrogen emissions were also investigated in a direct comparison between natural gas and gasoline fuelling at constant engine torque.

The main conclusions from this work are that:

• fuel type and equivalence ratio have major influences on both total hydrocarbon and methane emissions,
• spark timing affects total hydrocarbon and methane emissions significantly,
• increasing engine speed decreases total hydrocarbon emissions for both fuels,
• during cold start and warm-up operations, gasoline emitted a much higher excess of total hydrocarbons at first start compared with natural gas, and
• exhaust gas recirculation gave lower oxides of nitrogen emissions for natural gas than for gasoline fuelling.