Turbocharger matching for non-road diesel engine based on parametric sweeping

Abstract: A certain number of turbochargers are usually selected according to calculation parameters to conduct the bench test with diesel engine and the best one among the several turbochargers will be chosen with the traditional turbocharger matching method. However, this method can't guarantee that the selected turbocharger is the best choice. Because the internal combustion engine is a highly nonlinear system, it is difficult to use specific mathematical formula to represent a certain relationship between a parameter and other ones. Parametric sweeping to calculate objective functions to find optima is an optimization. It computes the objective function by directly sweeping the factors and then finds the optima by checking the sweeping results against the constraints. The parameter sweeping method is usually restricted to only one or two deign factors, because it is difficult to plot the parametric data of more than three factors. Meanwhile, the turbocharger matching just has two factors, i.e., compressor and turbine. Therefore, based on the design and development demand of a non-road diesel engine, a turbocharger matching method conducted by parametric sweeping was put forward, the corresponding turbocharged diesel engine model was developed according to the primarily selected turbocharger with GT-Power software as a carrier. In order to choose the best compressor and turbine, parametric sweeping study of normalized compressor mass multiplier and normalized turbine mass multiplier was conducted. The effects of compressors and turbines of different sizes on air-fuel ratio, brake specific fuel consumption, peak cylinder pressure and exhaust manifold temperature were analyzed. The final turbocharger having a good matching with diesel engine was selected under the conditions of the diesel engine design objective and durability constraints. However, the cylinder pressure and temperature will significantly increase when the internal combustion engine is equipped with a turbocharger, and both of the mechanical loading and thermal loading will increase, too. In order to weigh peak cylinder pressure (an indicator of mechanical loading) and exhaust manifold gas temperature (an indicator of thermal loading) after turbocharged, the parametric sweeping simulations of the boost pressure and start of combustion were also conducted. The two appropriate parameters were determined based on the simulation results under the durability constraints. The bench test showed that the selected turbocharger matched well with diesel engine, and the power capability, fuel economy, low-end torque and emissions targets have all reached the design requirements. The diesel engine durability constraints were also within the scope of the limit. Parametric sweeping study displayed the effects of compressors and turbines of different sizes, boost pressure and start of combustion on the diesel engine performance visually. It also can replace the complicated adjustment process of the real turbocharger matching and provide a reference guide for the actual calibration work. In addition, it can effectively balance the contradiction between the peak cylinder pressure and the exhaust manifold gas temperature by the calibration of the boost pressure and start of combustion reasonably.