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The Association of European Vehicle Manufacturers (ACEA) has undertaken a commitment to reduce average CO2 emissions to 140 g/km by the year 2008. This represents a reduction of 25% when set against the figures recorded back in 1995. Vehicle concepts based on CNG (Compressed Natural Gas) contribute to lowering CO2 emissions. Because natural gas is not yet extensively available at filling stations, it should also be possible for the engine to be run on gasoline. more...

Linear and non-linear low Reynolds number k-ɛ eddy viscosity models are applied to the simulation of unsteady transitional flows pertinent to axial turbomachine aerodynamics. Adequate test cases are selected to allow an individual investigation of wake velocity and wake turbulence effects on unsteady transition induced by separation bubbles and wake passing respectively. Separation bubbles under steady main flow conditions are calculated first, demonstrating the applicability of the numerical scheme and the selected turbulence models. Unsteady simulations show that essential features of the experimental investigation can be reproduced, although oscillation characteristics of the separation bubble, such as phase shifts, can only be partly reproduced. Predictions of wake-induced transition on a flat plate agree with the underlying direct numerical simulation study in many important aspects. However, simulation results show deficiencies with respect to the time-averaged transition length and the spatio-temporal evolution of turbulent flow regions. more...

In view of tight emission standards, injection strategies to reduce raw HC-emissions during the cold starting of port fuel injected engines are evaluated in this study. The relevance of spray targeting and atomization is outlined in the first part of this paper. The foundation and performance of different injector concepts with respect to spray characteristics are discussed. Laboratory experiments demonstrate that concepts relying on auxiliary energy, such as air-assistance, fuel heating and injection at elevated system pressures, are capable of producing spray droplet sizes in the SMD-range of 25μm. For future injection strategies aimed at the compliance of SULEV emission levels, this target value is considered to be essential. In the second part of this paper, emission tests of selected injector concepts are carried out using a V6-3.21 ULEV engine operated both in a vehicle and on a test bench. In this context, the relevance of an optimized start calibration as well as defining engine operating boundary conditions is discussed. Improving the fuel flow inside current injector designs already yields a 20-30% reduction of raw HC-emissions during cold starting. Significant reductions in the range of 40-50% are achieved by means of heated-tip injectors and fuel injection at elevated system pressures. Additionally, an FTP75 test series for selected concepts is presented. more...