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With alternative fuels having moved more into market in light of their reduction of emissions of CO2 and other air pollutants, the spark ignited internal combustion engine design has only been affected to small extent. The development of combustion engines running on natural gas or Biogas have been focused to maintain driveability on gasoline, creating a multi fuel platform which does not fully utilise the alternative fuels’ potential. However, optimising these concepts on a fundamental level for gas operation shows a great potential to increase the level of utilisation and effectiveness of the engine and thereby meeting the emissions legislation. The project described in this paper has focused on optimising a combustion concept for CNG combustion on a single cylinder research engine. The ICE’s efficiency at full load and the fuels characteristics, including its knock resistance, is of primary interest - together with part load performance and overall fuel consumption.

A standardized measurement setup and definition of compressor surge is yet to be established in the automotive community. As a consequence, compressor comparisons with regards to compressor operating map width is practically impossible today. This paper presents a possible solution to the described problem by presenting a suitable instrumentation and a correlation between measured values and actual NVH limits normally encountered in turbocharged vehicle applications. The work has been performed in laboratory conditions in a compressor test rig with both steady and pulsating flow as well as in a gas stand with steady flow. The test rig design, measurement setup and error sources are described. Some effects of different boundary conditions to the compressor and how they affect the measurement method are also presented.

Six closely matched turbochargers with variable geometry turbines, VGT, were benchmarked and investigated on a 2 litre spark ignited,SI, engine in order to evaluate their on-engine performance regarding the operating range of the VGT concepts and the ability of the turbine to deliver power to the compressor. The VGT turbines effect on engine operating conditions such as pre-turbine pressure that affects the engine output are also evaluated as well as the engine torque itself. The engine tests included performance at low engine-speed and at high engine-speed, transient response and a turbocharger flow capacity and matching check. Based on the engine test results three VGT concepts were further analyzed, in cold start emission testing and gas-stand testing. Gas-stand test result singled out one VGT concept as the most suitable for SI engines with regards to combined efficiency and flow capacity.