Converting the compression artio of a spark ignition engine to variable and effects on performance

in CONVERTING THE COMPRESSION RATIO OF A SPARK IGNITION ENGINE TO VARIABLE AND ITS EFFECTS ON PERFORMANCE (Ph.D.Thesis) M. Bahattin ÇELİK GAZİ UNIVERSITY INSTITUTE OF SCIENCE AND TECHNOLOGY February 1999 ABSTRACT Studies on improving the fuel economy in gasoline engine vehicles have been gained more importance day by day. Since, generally the vehicles have been used in urban traffic, studies on improving the fuel economy have been done on urban cycle driving. Engines have run at part loads in urban cycle. Volumetric efficiency is lower at part loads, so engine effective compression ratio decreases (e.g. from 8/1 to 3/1-4/1), engine efficiency decreases and fuel consumption increases. Engine performance can be increased by high compression ratio at part load working. In this study, spark ignited, single cylinder, four cycle, air cooled and 5/1 compression ratio engine have been used. This engine's compression ratio has been converted variable condition and the effects of variable compression ratio on engine performance at part loads have been investigated experimentally. In order to convert the basic engine to variable compression ratio engine (VCR), a modified cylinder head with auxiliary combustion chamber was used. VCR engine compression ratio T.C YteSEKÖ?RITİM KURULU DOKÜMANTASYON MfMCfZtIV was designed as variable between 4/1 and 10/1 and variability of compression ratio was provided during the engine operation. VCR engine and basic engine was compared accoding to results of experiments. Important improvements were gained on specific fuel consumption with VCR engine specially at part load. Specific fuel consumption of VCR engine at part load-high speed was 29 % less than basic engine. In addition, while CO exhaust emission at VCR engine operation was gained almost 10 % decrease with compare to basic engine, it was provided almost 25 % increase at HC exhaust emission. Effects of some operating parameters on knock-limited compression ratio was investigated. It revealed that the increase of ignition timing and engine load decreases knock-limited compression ratio. Science Code : 225.06.01 Key Words :Variable compression ratio, performance, knock Page Number : 142 Adviser : Prof. Dr. Mustafa BALCI