In-Cylinder Measurements of Wall Layer Hydrocarbons in a Spark Ignited Engine

Abstract

The hydrocarbon emissions process for the conventional, spark ignited, IC engine has been studied experimentally using a rapid acting gas sampling valve mounted in the combustion chamber wall. The sampling valve was electrohydraulically actuated. Design of the valve specifically allowed sampling in the vicinity of the wall quench layer with minimum leakage and crevice contributions to the measured hydrocarbon concentrations. Experimental results presented give substantial evidence that hydrocarbons remaining in a wall quench layer are not a major source of exhaust hydrocarbon emissions. Measurements of species concentrations as a function of time in the cycle and sample flow rate indicate that after flame arrival and quenching at the cold walls, hydrocarbons in the quench layer are rapidly and extensively oxidized within 2 msec. By use of an analytical model for the gas flow profile into the sampling valve, conservative upper limit calculations have been made of the quench layer contribution to the exhaust hydrocarbons for a number of engine operating conditions. These upper limit estimates show that quench layer hydrocarbons contribute no more than 3 to 12% to the hydrocarbons observed in the exhaust gases, depending upon the engine operating conditions. Hydrocarbons from other sources such as ringcrevice storage, and absorption-desorption of fuel from oil layers and surface deposits appear to be more important. Finally, evidence has been obtained for incomplete combustion of hydrocarbons in the bulk gas under homogeneous fuel-rich conditions.