Cylinder pressure sensors for smart combustion control

Abstract

Abstract. Different sensor concepts for time-resolved cylinder pressure monitoring of combustion engines are realized and evaluated in this paper. We distinguish a non-intrusive form of measurement outside the cylinder, performed by means of a force compression rod from intrusive, real in-cylinder measurement by means of pressure membrane sensors being exposed to the hot combustion process. The force compression rod has the shape of a sine wave with thinner zones equipped with highly sensitive foil strain gauges that experience a relatively moderate temperature level of 120 ∘C. The sensor rod delivers a relative pressure value that may be influenced by neighbour cylinders due to mechanical coupling. For the intrusive sensor type, two different materials for the membrane-type sensor element were simulated and tested, one based on the ceramic zirconia and the other based on stainless steel. Due to the higher thermal conductivity of steel, the element experiences only 200 ∘C while the zirconia element reaches 300 ∘C. Metallic chromium thin films with high strain sensitivity (gauge factor of 15) and high-temperature capability were deposited on the membranes and subsequently structured to a Wheatstone bridge. The pressure evolution can be measured with both types in full detail, comparable to the signals of test bench cylinder pressure sensors. For the preferential steel-based sensor type, a reliable laser-welded electrical connection between the thin films on the membrane and a copper wire was developed. The in-cylinder pressure sensors were tested both on a diesel test bench and on a gas-fired engine. On the latter, an endurance test with 20 million cycles was passed. Reliable cylinder pressure sensors with a minimum of internal components are thus provided. The signals will be processed inside the sensor housing to provide analysis and aggregated data, i.e. mass fraction burned (MFB50) and other parameters as an output to allow for smart combustion control.

Combustion Stability Control Based on Cylinder Pressure for High Efficiency Gasoline Engines

“…Usage of any cylinder pressure sensor able to provide a high frequency signal allowing an IMEP computation could be suitable for the control strategy, interested readers can refer to [20,21], for example.…”

Smart in-cylinder pressure sensor for closed-loop combustion control

“…The main components of the smart cylinder pressure sensor are the sensing element, the sensor housing, and the internal electronics. In a previous work (Vollberg et al, 2019) we presented and investigated different sensor designs with respect to the geometrical dimensions of existing combustion engine test benches. These are both non-intrusive pressure-sensing elements, which are equipped with highly sensitive foil strain gauges, and intrusive membrane-based sensors, which are coated with thin piezoresistive and temperature-stable thin films.…”

“…The electrical connection was realized by laser welding of copper wires onto the pads, a process specially developed to create reliable and temperature-stable connections described in detail in a previous paper (Vollberg et al, 2019). For a stable mechanical connection, the membrane-sensing element was laser-welded at the front end of the tube-like support (Fig.…”

“…Therefore, it is important to measure and control the process of combustion directly in the cylinder. In a previous paper (Vollberg et al, 2019), we analysed the international scientific status of cylinder pressure measurement and developed and compared different sensor approaches of our own. The work actually presented is based on the most advantageous pressure sensor concept, which is now extended by a sensor-related electronics which calculates some aggregated and meaningful combustion parame-ters from each pressure signal and forwards only these values to the engine control unit.…”

“…However, the concept of reliable pressure transducers designed for the harsh environment in modern combustion engines mainly depends on cost effectiveness, production capability, long-term stability, and packaging requirements. Different concepts for the transformation of pressure into the respective electrical value range from non-intrusive (Sellnau et al, 2000) to intrusive direct-pressure measurement types (Hellemans et al, 2011) using a large variety of physical effects like piezoelectricity, piezoresistivity, and optical fibrebased detection of light reflection of a membrane (Wlodarczyk, 2012), also mentioned in Vollberg et al (2019). For example, the Kistler company offers spark-plug-based pressure sensors working as piezoelectric, intrusive types.…”