Time-Resolved Measurements of Hydrocarbon Mass Flowrate in the Exhaust of a Spark-Ignition Engine 720112

Experimental measurements of the instantaneous exhaust gas temperature, mass flowrate, and hydrocarbon concentration have been made in the exhaust of a single cylinder research engine. The temperature measurements were accomplished using an infrared optical technique and observing the radiation of the exhaust gas at the 4.4 μm band of CO₂. Instantaneous exhaust gas mass flowrates were monitored by placing a restriction in the exhaust manifold and measuring the instantaneous pressures across the restriction. Time-resolved hydrocarbon concentrations were measured using a fast-acting sampling valve with an open time of 2 ms. From these measurements, the hydrocarbon mass flowrate is calculated as a function of crank angle. The hydrocarbon mass flowrate calculations show that approximately 40% of the hydrocarbons leave the cylinder early in the exhaust process, due to the exit of the head quench layer, and 50% leave the cylinder near the end of the exhaust process, due to the exit of a hydrocarbon-rich vortex produced by the upward motion of the piston. The remainder of the hydrocarbons leave in the middle of the exhaust stroke. The measurements explain why a reduction of the quench volume, created by the clearance between the piston and the first compression ring, reduces average hydrocarbon concentrations.