COMBUSTION CHAMBERS - National Institute of Technology

INTERNAL COMBUSTION ENGINES (ELECTIVE) (ME667)SIXTH SEMESTEROver head valve or I head combustion chamber ( VTU JULY( VTU JULY 2007/ / August 2005)The disappearance of the side valve or L-head Ldesign was inevitable at highcompression ratio of 8 : 1 because of the lack of space in the combustion chamber toaccommodate the valves. Diesel engines, with high compression ratios, invariably usedoverhead valve design.Since 1950 or so mostly overhead valve combustionchambers are used. This type of combustion chamber hasboth the inlet valve and the exhaust valve located in thecylinder head. An overhead engine is superior to side valveengine at high compression ratios.The overhead valve engine is superior to side valve or L-Lhead engine e at high compression ratios, for the followingreasons:o Lower pumping losses and higher volumetricefficiency from better breathing of the engine fromlarger valves or valve lifts and more direct passageways.o Less distance for the flame to travel and therefore efore greater freedom from knock,or in other words, lower octane requirements.oooLess force on the head bolts and therefore less possibility of leakage (ofcompression gases or jacket water). The projected area of a side valvecombustion chamber is inevitably greater than that of an overhead valvechamber.Removal of the hot exhaust valve from the block to the head, thus confining heatfailures to the head. Absence of exhaust valve from block also results in moreuniform cooling of cylinder and piston.Lower surface-volume ratio and, therefore, less heat loss and less air pollution.o Easier to cast and hence lower casting cost.Jagadeesha T, Assistant Professor, Department of Mechanical Engineering, Adichunchanagiri Institute of Technology, Chikmagalur