Comparison of Turbocharger Performance Between Steady Flow and Pulsating Flow on Engines 940839

In the fields of the internal combustion engines for automobile and marine use, higher output power, higher efficiency and lower fuel consumption are strongly expected. The problems of environment such as a global greenhouse effect or an acid rain is getting worse. Therefore the exhaust gas regulations had been introduced and being strengthen in the USA, Europe and Japan. These regulations demand the reduction of NOx and particulate matter(PM) from diesel exhaust gas at the same time. The turbocharging has been more important technique for these regulations. For automobile engines, it is common to use the pulse turbocharging system for compactness and advantage of response. The characteristics of compressor and turbine are different from under steady state condition by pulsating flow. Especially, it is difficult to estimate the performance of turbine mounted on engine by using the map measured under steady state flow.

It is the key point to know the difference of characteristics between on engine condition and steady state condition. It helps one to develop the high performance turbocharging and to select the optimum turbocharger specification. Many researchers had been investigated the characteristics of turbocharger under non-steady flow conditions^{(2),(4)∼(8)}. The most of them used the pulse generator to simulate the exhaust pulse of engine. They relate the characteristics of turbocharger on engine condition to steady state performances with quasi steady state method. For this method, they use the instantaneous turbine inlet and outlet pressure, temperature and mass flow rate. These approaches, which use the instantaneous data, are not suitable to one, who wants to select the turbocharger specification to a target engine. Usually they cannot get such data. They can get the information such as number of cylinders and type of exhaust manifold arrangement. It is desirable that they can estimate the turbocharger performance on the engine without any instantaneous data.

Authors used the actual engines instead of a pulse generator to compare the flow and efficiency characteristics between on engine condition and steady state condition. From results of these approaches, it is found that engines having the same exhaust system have the same tendency of mass flow and efficiency correction coefficient for the turbine expansion ratio. From results of the measurements of degree of reaction in a turbine scroll, the amplitude of variation measured on engine is greater than for steady state flow. It means that the estimate with quasi steady state approach for non-steady state flow condition brings some errors.