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The primary objective is to gain temperature control. When air is compressed the temperature increase. Cooling the air to room temperature after compression reduce the peak temperature during combustion substantially, typically 500K, hence dramatically reducing the formation of NOx.
The Hedman cycle was verified November 2000. A Briggs & Stratton engine with pneumatic valve actuators was run on Hydrogen fuel. The level of NOx was not measurable with state-of-the-art equipment. Another feature of the Hedman cycle is that it provides a wide torque span. The engine may be run temporarily with 100% compressor strokes providing massive engine braking or with 100% power strokes. |
The torque of power strokes may also be varied within wide a range, since it is possible to gain torque by keeping the inlet valve open up to 45 degrees beyond top dead center and then start combustion. This would increase the combustion chamber volume about 250% (if the compression ratio is 10:1).
Since air at room temperature has twice the density of the normal air density after compression it would be possible to combust 2,5*2=5 times the amount of fuel in one power stroke compared to an Otto cycle. Since the power cycle is 2 stroke and hence may be repeated with double the Otto frequency the conclusion is that with the Hedman cycle it is temporarily possible to increase the torque 10 times compared to Otto. |
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Hedman Combustion Cycle
The cycle may be described as an Otto cycle where the compression cycle is separated from the combustion and expansion cycle with an intermediary cooling of the compressed air.
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