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In modern spark-ignited engines the accurate estimation of the amount of fuel to be injected is an important issue, in particular if a specific air-to-fuel ratio is required. The knowledge of the events occurring between the intake duct (injectors) and the exhaust duct (λ-sensor) is thus very important. Among all the systems that play a role, the best studied are the wall-wetting dynamics. Nowadays, the wall-wetting effects are compensated on the basis of simple linear models that are tuned with the help of a large number of measurements. These models are quite effective but they cannot be used universally.Their extrapolation for a non-measured operating point can lead to unsatisfactory results. Other problems arise at operating points where direct measurements are difficult, e.g., at cold start. Complex models already exist, but usually they require a lot of work in the parameterization phase.

The measurement of the various pollutant species (HC, CO, NO, etc.) has become one of the main issues in internal combustion engine research. This interest concerns not only their quantitative measurement but also the study of the mechanism of their formation. In fact, pollutant species concentration can be used as an indicator for the combustion characteristics. For instance, it enables the determination of a lean or a rich combustion, the percentage of EGR, etc. The purpose of this research is to investigate the behavior of pollutant gas particles in the first part of an engine exhaust system through a detailed study of the unsteady flow in the exhaust pipe. The results are intended to designate the appropriate sensor positions which ensure accurate measurement results. This investigation wants to track an inert component in the exhaust system, namely the NO gas.

The burned gas remaining in the cylinder after the exhaust stroke of an SI engine, i.e. the residual gas fraction, has a significant influence on both the torque production and the composition of the exhaust gas. This work investigates the behavior of the residual gas fraction over the entire operating range of the engine. A combined discrete-continuous linear model is identified, which describes the dynamic effects of the gas composition from when the gases enter the cylinder up to the measurement with a specific sensor. In this investigation, that sensor is a fast NO measurement device. The system is modelled by three elements in series: the in-cylinder mixing, the transport delay, and the exhaust mixing. The resulting model contains three elements in series connection: the in cylinder mixing, the transport delay, and the exhaust gas mixing. The model is able to calculate the fuel mass entering the cylinder during a fuel injection transient.