Analysis of Nitric Oxide Formation in Spark Ignition Engine with Heat Transfer and Effect of Ignition Point

The formation of nitric oxide in the combustion chamber of a spark ignition engine is formulated by developing a simple model. The state of the gas in the chamber and its thermal properties are estimated during a complete cycle. The estimation of the nitric oxide formation is based on the Zeldovich mechanism and assumes the burned gas either in a fully mixed or unmixed state. A simple heat transfer relation is used to estimate the heat loss from the gas to the chamber walls. The effect of the position of the ignition source relative to the exhaust port is also taken into account, and the predicted nitric oxide concentrations are compared with experimental results from a single-cylinder variable compression ratio IFP engine.

It is found that the nitric oxide concentration predicted by the model agrees well over most of the operating range with the experimentally measured nitric oxide concentrations in the exhaust gas. The effect of the location of the flame initiation point with respect to the exhaust port is also interesting. When the flame is initiated nearer the exhaust valve, the nitric oxide concentration is higher in the exhaust than when the flame is initiated at a point farther from the exhaust valve.