Development of the tracer gas method for large bore natural gas engines - Part I: Method validation

The tracer gas method is investigated as a means to study scavenging in fuel-injected large-bore two-stroke cycle engines. The investigation is performed on a Cooper-Bessemer GMV-4TF natural gas engine, with a 36-cm bore and a 36-cm stroke. Two important parameters are evaluated from the tracer gas measurements, which are scavenging efficiency and trapped A/F ratio. Measurements with the tracer gas method are compared with in-cylinder sampling techniques to evaluate the accuracy of the method. Two different tracers are evaluated, monomethylamine and nitrous oxide. Monomethylamine is investigated because of its common use historically as a tracer gas. Nitrous oxide is a new tracer gas that overcomes many of the difficulties experienced with monomethylamine. The tracer gas method with nitrous oxide is determined to be accurate for evaluating scavenging efficiency and trapped A/F ratio in comparison to the in-cylinder sampling techniques implemented.