Diesel engines have made a lot of progress in the last few decades and engine electronic controls have played a big role in this success. This research presents a sensor for the ion current in the cylinder that can be used for feedback engine electronic control. This is an inexpensive on-board sensor that can be applied in multi cylinder engines.
The ion current signal from gasoline engines using the spark plug has been well investigated . This is not the case in diesel engines. In this work on a single cylinder diesel engine, the glow plug was modified to act as an ion sensor in addition to being a glow plug. This approach does not require any extra holes in the cylinder head of the engine.
This study showed two peaks for the ion current. The first peak occurs shortly after the peak of rate of heat release and the second peak occurs later in the expansion stroke. The effect of speed, load, injection pressure and injection timing on the magnitude and location of each of the two peaks has been determined. The modified glow plug has been found to be successful in producing the ion current signal, in addition to being a glow plug. It has been concluded that the ion current signal can be a good indicator of the start of combustion and the rate of heat release under different engine operating conditions. . The two peaks vary in different ways under the different engine operating conditions examine in this work.
