ICCC – Ion-Current Combustion Control
Ion-Current Sensor based Closed-Loop Control of Lean Gasoline Combustion with High Compression Ratio
Lean combustion processes offer high potential for improving the efficiency of gasoline engines, especially in combination with a further reduction in throttle losses and higher compression ratios. Homogenous Charge Compression Ignition (HCCI) can reduce NOx raw emissions by up to 99% compared to a conventional spark-ignited (SI) lean-burn process. Lean-burn combustion processes are very sensitive to changing global and local combustion chamber conditions, that cannot be measured directly.
Accordingly, lean combustion, especially HCCI, has major disadvantages in terms of controllability. Fluctuations of the charge state cause cyclical fluctuations of the combustion with strong effects on efficiency, emissions and combustion stability. The working hypothesis of the applicants is that the ion current signal provides additional information on the state of the cylinder charge, which can improve the controllability of lean-burn combustion.
The fast analysis of the ion current requires new hardware and software approaches and have not yet been investigated in detail. In addition, the analysis circuits used to interpret the ion current signal must be significantly improved. A systematic methodology is required to identify the optimal electrical sensor layout and signal processing algorithm. SI combustion, especially with high compression ratios, faces challenges by the pre-ignition of the cylinder charge. For the active prevention of these phenomena a fast and reliable identification of the pre-ignition is necessary.
An innovative analysis of weak ion current signals is necessary to provide additional information about the cylinder charge and allows to establish new FPGA-based in-cycle control algorithms. Frequency domain analysis with digital signal processing is a promising approach for use in fast in-cycle control algorithms to stabilize lean combustion. In this project, the applicants aim a deeper understanding of the correlations of the ion current sensor signal and the underlying chemical and physical effects in the cylinder charge and the resulting conductivity, combining a detailed simulation with investigations on test benches in Shanghai and Aachen to improve measurement and signal processing. The analysis circuit will be adapted to improve the signal-to-noise ratio. The identified correlation between the ion current and the cylinder charge state will be used to perform a feasibility study for a new FPGA-based in-cycle control algorithm.