Emissions regulations for off-highway engines are tightening towards those of on-highway engines. Present designs will not be able to meet these more stringent regulations because of their use of mechanical fuel injection timing control; more advanced timing control will be required. Ion sensing combined with variable fuel injection timing may help these engines meet the emissions requirements without the drastic price increase that usually accompanies a switch to advanced fuel injection technology. Ion sensing can detect the start of combustion and this signal can be used for closed loop control for the injection timing. The integrity of the ion signal is highly dependent on combustion chamber geometry, sensor placement, and even the polarity of the charge across the sensor. Optimizing all of these effects could improve the detection of the start of combustion from an ion sensor to less than one crank angle degree and provide a signal for closed loop control of the injection timing.

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