Technical Paper
Development of Pistons with Variable Compression Height for Increasing Efficiency and Specific Power Output of Combustion Engines.
1990-02-01
900229
The significantly poorer efficiency of a spark-ignition engine in the part load range compared to its efficiency at full load is the result on the one hand of the restriction losses and on the other hand of the severe combustion lag. It would be a conceivable proposition to considerably improve part load efficiency (10 % at bmep = 3 bar) by increasing the compression ratio although this is impeded by the risk of knocking combustion at full load. In combination with variable valve timing (this requires variable compression ratio) even 19 % efficiency improvement are achievable (1). This has given rise to a joint development programme between Mahle GmbH and Daimler-Benz. Research aimed at producing a piston with a variable compression height which can thus offer optimum compression ratio at every point of the map.
