Spark ignition IC engine - has inlet valve timing to make compression and expansion ratios different

摘要

The engine has a piston reciprocating in a cylinder with cam operated inlet and exhaust valves. The inlet valve opens (I) at TDC. It remains open for the whole of the suction stroke (II) and does not close until the piston has started to return (III) upwards. Part of the charge is thus returned into the suction manifold and only part of the stroke used for compression. After ignition by a spark at or near TDC expansion takes place over the whole of the working stroke of the piston. The expansion ratio is thus > the compression ratio. This enables more work to be extracted from the gases for a given compression ratio and thus increases the efficiency.