(1) Operation cycle - a closed cycle consisting of four operation processes: intake, contraction, work and exhaust. Only if these processes are carried out again and again, can the internal combustion engine work continuously.
(2) Upper and lower dead ends - the farthest distance between the piston top and the crankshaft revolving center, i.e. the highest orientation of the piston, is called upper dead ends; the nearest place between the piston top and the crankshaft revolving center, i.e. the lowest point of the piston, is called lower dead ends. At the top and bottom dead ends, the piston moves at zero speed.
(3) Crank radius - crankshaft turning radius R.
(4) Piston stroke - the interval S between upper and lower dead ends. S=2R.
(5) Cylinder Operation Volume - Volume Vh Sweeped by Piston from Top-dead-point to Bottom-dead-point
(6) Combustor Volume - Volume Vc formed between the top of the piston and the bottom of the cylinder head when the piston is located at the top dead center.
(7) Total Cylinder Volume - Va of the sum of Cylinder Operating Volume and Combustion Chamber Volume. Va = Vc + Vh.
(8) Compression Ratio - The ratio of volume before gas compaction to volume after gas compaction, i.e. the ratio of total cylinder volume to combustion chamber volume. Compression ratio is a very important concept in engine, which indicates the degree of gas compaction.
（9）发动机排量——多缸发动机各气缸作业容积的总和VL。VL=Vh×I；其间， Vh—气缸作业容积； I—气缸数目。
(9) Engine displacement - VL of the total operating volume of each cylinder of a multi-cylinder engine. VL = Vh * I; Vh - cylinder operating volume; I - cylinder number.
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