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This paper describes the experimental study of a tumble-flap mounted in the intake port of a single-cylinder spark-ignited gasoline engine. The research question addressed was whether an optimal tumble level could be found for the combustion system under investigation. Indicated fuel consumption was measured for a number of part-load operating points with the tumble-flap either open or closed. The experimental results were subjected to an energy balance analysis to understand which portion of the fuel energy was converted to work and how much was lost by incomplete combustion, heat losses to walls and to the exhaust gases, as well as to pumping losses. Closing the tumble-flap resulted in reduced fuel consumption only in a small area of the operating map: only at low-speed, low-load operation, a benefit could be obtained.

Direct gasoline injection combined with turbo charging and down sizing is a cost effective concept to meet future requirements for emission reduction as well as increased efficiency for passenger cars. It is well known that turbulence induced by in-cylinder air motion can influence efficiency. In this study, the intake-generated flow field was varied for a direct injected turbo charged concept, with the intent to evaluate if further increase in tumble potentially could lead to higher efficiency compared to the baseline. A single cylinder head with flow separating walls in the intake ports and different restriction plates was used to allow different levels of tumble to be experimentally evaluated in a single cylinder engine. The different levels of tumble were quantified by flow rig experiments.

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.