Micro-thermal CMOS-based gas quality sensing for control of spark ignition engines

• A sensor was developed which is able to detect gas quality of a gas mixture.
• The sensor measures thermal conductivity, heat capacity, and density.
• The sensor was integrated in the fuel supply line of an internal combustion engine.
• It is possible to correlate a variety of engine responses to the sensor output.
• A two-step correlation procedure without a-priori knowledge of the gas is used.

Internal combustion engines fueled with natural gas have to be adjusted to the fuel properties in order to achieve maximum efficiency, minimum pollutant emissions and good long-time integrity of all components. Normally, gas quality is neither measured nor used a as control input. Therefore, engines do not necessarily react correctly to changing gas qualities. This paper describes how a micro-thermal CMOS gas quality sensor is used to directly correlate engine parameters (for example knock tendency, and exhaust gas recirculation tolerance) from basic physical properties of a gas mixture. Doing direct correlation for a certain engine, there is no need any more to correlate engine reactions (e.g., knock) to fuel quality parameters determined on completely different engines (e.g., methane number). The formal correlation procedure also offers insight into the underlying physical process when choosing correlation input functions of weighted terms of thermal conductivity, heat capacity and density and re-factoring these terms.

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