Search Results

Continuously Variable Cam Phasers (CVCP) controlling both the exhaust and intake camshaft phasing in combination with air assist direct fuel injection and a wide variable spark gap is utilized to reduce the fuel consumption for a 4-valve Turbo Charged (TC) Spark Ignition (SI) engine. The spark plug and the air-assisted direct fuel injector are integrated into one unit in order to facilitate packaging in a modern 4-valve combustion chamber. This integrated component is referred to as the Spark Plug Injector (SPI). CVCP's are used to reduce pumping work by diluting the charge with large amounts of residual exhaust gas. This strategy, along with stoichiometric homogeneous operation enables the use of a Three Way Catalyst (TWC), considered to be a prerequisite to meet the emission standards of Ultra Low Emission Vehicles (ULEV) II and beyond. The ignition quality deteriorates with increasing levels of residual exhaust gas dilution.

The effect of the electrodes on the early signal of the ionization sensor has been studied experimentally and with a model for the sensor. Experiments in a constant-volume combustion chamber with a generic electrode configuration allowed to investigate the role of electrode contact and the main path of the current. A framework for a model allowing the inclusion of electrode processes is introduced, and a first implementation of this model is presented. The results from the simulations are in good qualitative agreement with the experimental observations. Our conclusion is that electrode processes can limit the current during early combustion, and that the geometry of the electrodes, and especially the cathode, govern the characteristic shape of the first current peak.

A combined experimental and theoretical effort has been made to identify the most important contributors to equilibrium ionization in the post-flame gas. In the past, nitric oxide (NO) has always been assumed to be the main electron donor in the compressed hot post-flame gases. However, correlations observed between the amount of NO in the exhaust gases and the current amplitude may be deceiving due to the fact that both the formation of NO and the ionization process are strongly temperature dependend. The temperature-current relationship in data from various experiments in constant volume combustion chambers and engines was utilized to check the hypothesis that NO acts as the major contributor to ionization. Based on a well-motivated model for the current, the effect of temperature and electron donor concentration has been separated.

The location of the peak pressure can serve as a control parameter to adjust ignition timing and optimize engine performance. The ionization sensor, an electrical probe for combustion diagnostics, can provide information about the peak pressure location. However, the reliability of such information is rather poor. In-cylinder gas flow at the electrodes may be one reason for this. We present results from an investigation of the relationship between ionization sensor current and pressure under various gas flow conditions. The gas flow velocity in the vicinity of the electrode gap was measured by LDA. From the results one may infer how the in-cylinder gas flow affects the reliability of the prediction of pressure peak location from the ionization sensor signal. One finding is that high bulk gas flow impairs the precision of the prediction in certain configurations.

The use of a spark plug as an ionization sensor in an engine, and its physical and chemical explanation has been investigated. By applying a small constant DC voltage across the electrodes of the spark plug and measuring the current through the electrode gap, the state of the gas can be probed. An analytical expression for the current as a function of temperature is derived, and an inverse relation, where the pressure is a function of the current, is also presented. It is also found that a relatively minor species, NO, seems to be the major agent responsible for the conductivity of the hot gas in the spark gap.

An ionization sensor has been used to study the combustion process in a six-cylinder lean burn, truck-sized engine fueled with natural gas and optimized for low emissions of nitric oxides. The final goal of the investigations is to study the prospects of using the ionization sensor for finding the optimal operating position with respect to low NOx emission and stable engine operation. The results indicate that unstable combustion can be detected by analyzing the coefficient of variation (CoV) of the detector current amplitude. Close relationships between this measure and the CoV of the indicated mean effective pressure have been found during an air-fuel ratio scan with fixed ignition advance.

The spark energy delivered to the gas has been measured calorimetrically for five different ignition systems at six pressure points. Both inductive and capacitive systems have been investigated. Simultaneous electrical measurements were used to estimate the fraction of electrically stored energy actually deposited in the gas time-resolved for two systems. A separation of breakdown and glow energy was attempted using a simple model for the heat distributed to the gas and the electrodes by the spark. The results are considered valuable for the understanding of spark energy deposition as well as the design of adaptable ignition systems.

A model based on an ionization equilibrium analysis, that can relate the ion current to the state of the gas inside the combustion volume, has been presented earlier. This paper introduces several additional models, that together with the previous model have the purpose of improving the pressure predictions. One of the models is a chemistry model that enables us to realistically consider the current contribution from the most relevant species. A second model can predict the crank angle of the peak pressure and thereby substantially increase the accuracy of the pressure predictions. Several other additions and improvements have been introduced, including support for part load engine conditions.