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2009 Issues Archive
19 August 2009
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Upgrade to 5-stroke petrol engine may reach diesel parity
Ilmor Engineering has run trials of a 5-stroke petrol engine it hopes will have fuel consumption and emission levels comparable to that of current diesel engines, without the problem of particulate and NOx emissions.
Initial tests on a proof of concept engine reveal a capacity of 700cc (turbocharged) and a peak power of 135bhp at 7000rpm. Peak torque is 166Nm at 5000rpm, with minimum fuel consumption of 226g/kWh.
The 5-stroke concept engine uses two fired cylinders (high pressure) operating on a conventional 4-stroke cycle which alternately exhaust into a central expansion cylinder (low pressure).
The low pressure cylinder decouples the expansion and compression processes and enables the optimum expansion ratio to be selected independently of the compression ratio.
The engine uses a rapid prototype cast cylinder head, a machined-from-solid cylinder block and separate electrically powered oil and water pumps. Two overhead camshafts operate the conventional coil spring valvegear with the high pressure camshaft running at 0.5 x crank speed and the low pressure camshaft running at 1 x crank speed.
The engine is turbocharged to increase the engine rating.
Running of a concept engine has produced impressive fuel consumption readings over a very wide operating range, says Northamptonshire-based Ilmor.
Primarily, this is because at the onset of knock a greater percentage of work can be extracted in the LP cylinder, giving a degree of self-compensation.
The engine runs an overall expansion ratio approaching that of a diesel engine – in the region of 14.5:1.
It requires minimised pumping work because of the downsizing effect from highly rated firing cylinders, and the compression ratio can be reduced to delay knock onset without a reduction in performance.
Ilmor says the engine uses conventional technology and requires no new manufacturing techniques. The firm is looking to produce a second-phase development engine for in-vehicle testing.
Steve O’Connor, engineering manager, said: “The performance characteristic of the 5-stroke, in that it has broad brake specific fuel consumption, means that it has potential as a serial hybrid engine.”
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© PE Publishing, 19 August 2009
