Experimental investigation of in-duct insertion loss of catalysts in internal combustion engines

Acoustic performance characteristics of catalysts in the exhaust system are important in the development of predictive tools for the breathing system of internal combustion engines. To understand the wave attenuation behavior of these elements with firing engines, dynamometer experiments are conducted on a 3.0L V-6 engine with two different exhaust systems: one with the catalysts on the cross-over pipe, and the other that replaces the catalysts with equal length straight pipes. The instantaneous crank-angle resolved pressure data are acquired at wide open throttle and 500 rpm intervals over the operating range of the engine (from 1000 to 5000 rpm) at various locations in both exhaust systems. The effect of the catalyst is then isolated and discussed in terms of insertion loss at critical locations in the exhaust system. The analysis is presented both in terms of time-domain and order-domain. The predictive capability of a finite-difference based time-domain nonlinear approach is also demonstrated as applied to large amplitude waves in the exhaust system of firing engines.