Split ratio control in mini–dilution tunnels for measurement of steady–state and transient emissions from heavy duty diesel engines

Abstract

A 91–tube multi–tube–type mini–dilution tunnel with and without a split ratio control unit was used to study the emissions from a heavy duty diesel engine, operated over several steady–state modes and transient test cycles. The split ratio, or the gas induction ratio, relates the volume of sampled raw exhaust to the total volume of engine exhaust that is generated. Determination of the split ratio and the ability to maintain this ratio around a certain theoretical value, 1/91 in the study, was critical to the entire sampling process. Results presented herein, demonstrate the ability of the split ratio control unit to improve dramatically the splitting accuracy of the 91–tube splitter, over both steady–state and transient cycles. Even when operated over severe changes in engine conditions of the transient cycles, the split ratio control unit was able to maintain an average pressure differential of nearly zero. However, the transient response of the PID controller needs further improvements.