Observer Design for Fuel Reforming in HCCI Engines Using a UEGO Sensor

Homogeneous Charge Compression Ignition (HCCI) combustion shows a high potential of reducing both fuel consumption and exhaust gas emissions. Many works have been devoted to extend the HCCI operation range in order to maximize its fuel economy benefit. Among them, fuel injection strategies that use fuel reforming to increase the cylinder charge temperature to facilitate HCCI combustion at low engine loads have been proposed. However, to estimate and control an optimal amount of fuel reforming in the cylinder of an HCCI engine proves to be challenging because the fuel reforming process depends on many engine variables. It is conceivable that the amount of fuel reforming can be estimated since it correlates with the combustion phasing which in turn can be measured using a cylinder pressure sensor. However, an accurate estimate is not expected since it is very difficult to isolate the effect of fuel reforming on combustion phasing from other engine variables that also affect the combustion phasing. In this paper, a model-based observer is designed to estimate the amount of fuel reforming in an HCCI engine using a UEGO (Universal Exhaust Gas Oxygen) sensor and its unique characteristic.