Closed Loop Control of the Combustion Phase in SI Engines Using Alternative Fuels

Abstract

Combustion engines using alternative and/or renewable fuels are vital to reduce emission of greenhouse gases. The property of such fuels may vary significantly. The heat release rate of bio and natural gas varies of natural reasons, which is known to cause problems when used in internal combustion engines. Hydrogen is an attractive renewable fuel that has a high potential to reduce greenhouse gas emission. Bio and natural gas can be mixed with hydrogen and the content may vary depending on the availability, e.g., depending on the production from solar and wind power. Variations in the fuel property reduces the engine efficiency, unless the combustion phase is estimated and the ignition (combustion) timing is adapted to compensate for the varying fuel property. Hereby the drivability can be improved, and the fuel consumption decreased significantly, reducing the total cost of ownership and emission of greenhouse gases. However, there is not yet any widespread industrially available technique to estimate the combustion phase. In-cylinder pressure measurement is not a practical solution due to cost and life-time issues. Here, a strategy for ion current measurement signal processing is proposed as a viable alternative to in cylinder pressure sensors by estimating the peak pressure location (PPL) from the ion current. The PPL estimate meets the robustness requirements of industrial applications. The approach is described and evaluated on engine measurements. The results show that ion sense can be used for PPL estimation and the standard deviation from one estimate to another is in the order of 1-2 CAD, which can be further reduced by averaging. The PPL estimates can be used in a closed control loop to compensate the ignition timing when the fuel property varies - saving cost and reducing greenhouse gas emission.