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

A 91-tube multi-tube-type mini-dilution tunnel with and without a split rat io control unit was used to study the emissions from a heavy duty diesel en gine, operated over several steady-state modes and transient test cycles. T he split ratio, or the gas induction ratio, relates the volume of sampled r aw exhaust to the total volume of engine exhaust that is generated. Determi nation of the split ratio and the ability to maintain this ratio around a c ertain theoretical value, 1/91 in the study, was critical to the entire sam pling process. Results presented herein, demonstrate the ability of the spl it ratio control unit to improve dramatically the splitting accuracy of the 91-tube splitter, over both steady-state and transient cycles. Even when o perated over severe changes in engine conditions of the transient cycles, t he split ratio control unit was able to maintain an average pressure differ ential of nearly zero. However, the transient response of the PID controlle r needs further improvements.