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The instantaneous flow from the exhaust pipe of a single cylinder two stroke engine was studied in this research. Three exhaust pipes were investigated. One is a simple pipe with an expansion chamber, and the other two are commercial exhaust pipes. The flow field in the exhaust pipe was calculated using the one-dimensional unsteady gas dynamic model. The instantaneous velocity of the exhaust flow was detected using a hot wire anemometer located at the exit of the exhaust pipe. The calculated pressure variations inside the chambers of the exhaust pipe agreed quite well with the measured data. The calculated instantaneous exhaust velocity also matched the measured velocity variations in cases where reverse flow did not occur. However, discrepancies occurred at low engine speeds because the hot wire anemometer can not distinguish between forward and reverse flow.

To formulate a computer model for a two-stroke engine, the boundary conditions have to be solved for cylinder or crankcase to pipe flow, pipe flow to atmosphere. The models to deal with the former and the latter are often called partially open end model and open end model respectively. In this paper, two types of models for partially open end and two for open end are investigated by comparing the predicted pressure data in the exhaust pipe. Also, two different ways to model transfer pipe are considered. One treats the flow in transfer pipes as quasi-steady flow while the other simulates that with an one-dimensional gas dynamic model. The simulation is based on a zero-dimensional thermodynamic model for cylinder as well as crankcase and an one-dimesional gas dynamic model for pipes. The former uses 4th-order Runge-Kutta method and the latter uses a combined 4th-order Runge-Kutta and two-step Lax-Wendroff (4RK/2LW) method.

Diesel engines possess high energy efficiency as for power generation, and they have been used in commercial vehicles widely for a long time. Due to the coming shortage of fossil fuel in the near future and the impact of greenhouse gas effect in recent years, the types and quantities of diesel vehicles have grown year by year. However, smoke emission of diesel engine has always been an issue. Diesel smoke can be seen by eyes apparently, and it becomes an obvious pollution problem. Traditional diesel particulate filter (DPF) is the current solution to solve the problem of smoke emission currently. However, after using DPF for a certain period of time, the back pressure of engine will rise up and the engine performance will be affected because of the accumulation of soot particles. The soot particles must be removed. This process is the regeneration of DPF.

In the development of the OBD system of a vehicle, an aged catalyst is required to test the function of the system. This catalyst is partially deteriorated and the emission after this catalyst will exceed the regulation value with limited bound according to the testing protocol. This aged catalyst is very valuable, and difficult to prepare. A bypass in the exhaust pipe was used to simulate the deterioration of catalyst in this paper to investigate the emission characteristics of a motorcycle engine. The degree of deterioration can be controlled by the portion of exhaust flow through the parallel pipe. This method of simulation has been conducted in a dynamometer testing. An electronic controlled motorcycle engine was used in this test. It was found that at low load condition, the CO and HC concentrations in the downstream of exhaust pipe were increased as the control valve was opened to let more and more exhaust to flow through the straight pipe.