> vehicle engineering Paul Kapus (ri.), Head of Gasoline Engine Development, and Matthias Neubauer (le.), Technical Expert High Performance Engines. > Two-stage compressor for optimum pressure ratios. 1 2 F O C U S Pressure 2-stage boosting with interstage cooling Compressor work saved 1-stage compression (2-st w/o interstage cooling) Volume Isothermal compression out exceeding 30 bar mean effective pressure requires an engine speed of 8000 rpm. The engine could also have been designed for as little as 6000 to 6500 revolutions per minute, but this would have required a mean effective pressure level of around 40 bar. Yet on the one hand this would have led to slower response behavior and on the other the torque demands placed on the remaining powertrain, such as clutch and transmission, would have been too large and we did want to use series components for clutch and transmission.” To make the engine durable at speeds up to 8000 rpm, we first had to take development measures to make the engine speed-resistant. For this purpose, our optimizations focused on the crankshaft, rods and pistons, which were provided with special cooling galleries, and the valve train. Apart from that, an improved cylinder head cooling system with cross flow concept was designed to help the engine withstand the extremely high thermal loads at maximum output: “It was crucial to give the cylinder head a design that would allow it to dissipate the high thermal load. This is essential for knock resistance and also durability. Obviously, an engine with such a high power density has an extremely high heat input – similar to that of a V8 bi-turbo engine, but in our case distributed across no more than four combustion chambers,” Matthias Neubauer explained. By utilizing a special fuel injection system from Bosch, designed for 350 bar, sufficient fuel flow was ensured – while maintaining strict compliance project, in which AVL used electric supercharging to boost efficiency, was the VW Golf HiEff. The aim of this concept engine was to demonstrate that by using a Miller-cycle engine with a high-pressure exhaust gas recirculation system with cylinder individual feed and an e-compressor, CO2 emissions in the NEDC test could be reduced from 122 g CO2/km down to 90 g CO2/km – without requiring hybridization. The e-compressor powered by 12 volt not only takes care of electric boosting but also acts as exhaust gas recirculation pump. In this concept, engine efficiency was raised to 40% in the sweet spot. THE AVL HYPER WITH 200 KW/L According to Matthias Neubauer, Technical Expert for High Performance Engines, it was a particular challenge for AVL to obtain the output of 474 hp (349 kW) from a 1.75-liter engine: “The problem we faced was that we wanted to focus on durability, but without leaving the family concept. However, to achieve a good response behavior at all speeds, the mean effective pressure should not go far beyond 30 bar. Achieving the target output with-
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