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Engine designers need an objective measurement which can be tested on the engine to indicate acceptable idle quality. An experiment was performed to select objective measures based on cylinder pressure data, and two measures were selected. Standard deviation of indicated mean effective pressure (SDimep) is a measure of the statistical instability of combustion. Lowest normalized value (LNV) is a measure of the tendency toward misfire. These two measures are shown for a set of typical engines. The body of data shows the relation of SDimep and LNV to burn duration and timing.

A 1.9L four cylinder engine was evaluated for leakage of cylinder charge through the exhaust valve seats. Fast FID HC analyzer traces reveal leakage. Static leakdown tests do not correlate with the Fast FID measurement, unlike previously published reports for a different engine. The causes of exhaust valve seat leakage are likely to be Flakes of cylinder deposits lodging in the valve seat Valve seat distortion due to the thermal and pressure loading of the cylinder head structure Because deposit related effects are very history dependent, it is very difficult to obtain quantitative results. Some experimental observations: Static pressure leakage measurements show variation of leakage area with cylinder pressure, caused by flexing of the valve head. Dynamic leakage results are history dependent. Leakage is reduced after running at high speed/load, and gradually build up during extended light load low speed operation.