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The spatial and temporal formation of nitric oxide in an optical engine operated with iso-octane fuel under spray-guided direct-injection conditions was studied with a combination of laser-induced fluorescence imaging, UV-chemiluminescence, and cycle resolved NO exhaust gas analysis. NO formation during early and late (homogeneous vs. stratified) injection conditions were compared. Strong spatial preferences and cyclic variations in the NO formation were observed depending on engine operating conditions. While engine-out NO levels are substantially lower for stratified engine operation, cyclic variations of NO formation are substantially higher than for homogeneous, stoichiometric operation.

Early Intake-Valve Closing (EIVC), which has been suggested to control the load of SI engines for a long time, is applied in this paper to control the load and the boost pressure of a turbocharged SI engine. Load control by means of EIVC reduces the pumping loss at the part load, and boost pressure control by means of EIVC eliminates the disadvantages of the conventional boost control system with wastegate and reduces the pumping loss at high speeds and loads. Another advantage of this control concept is the possibility to utilize the internal cooling effect of the charge when the intake-valve is closed before BDC. The lower compression temperature of the EIVC engine in comparison with the conventional engine is very helpful to reduce the tendency to knock and can be effectively utilized to improve the thermal efficiency.

GTL (Gas-To-Liquid) fuel is well known to improve tailpipe emissions when fuelling a conventional diesel vehicle, that is, one optimized to conventional fuel. This investigation assesses the additional potential for GTL fuel in a GTL-dedicated vehicle. This potential for GTL fuel was quantified in an EU 4 6-cylinder serial production engine. In the first stage, a comparison of engine performance was made of GTL fuel against conventional diesel, using identical engine calibrations. Next, adaptations enabled the full potential of GTL fuel within a dedicated calibration to be assessed. For this stage, two optimization goals were investigated: - Minimization of NOx emissions and - Minimization of fuel consumption. For each optimization the boundary condition was that emissions should be within the EU5 level. An additional constraint on the latter strategy required noise levels to remain within the baseline reference.

The growing availability of different biofuels and synthetic fuels is leading to increased diversity of automotive fuels. Understanding how fuel properties affect combustion and how engine calibration strategies can compensate for variations in fuel composition is crucial for ensuring proper engine operation in this world of increased fuel diversity. This study looks at the ability to compensate for wide changes in cetane quality. Four different fuels with variations in cetane number, volatility and composition have been tested in a single cylinder engine and compared to diesel fuel. The selected operating conditions represent the entire engine map of a passenger car diesel engine. In part load the effects were investigated for conventional and premixed Diesel combustion. The results show that part load operation is especially relevant for the detection and compensation of varying fuel properties and that, depending on engine load, different control strategies have to be applied.

This paper presents a new approach to the optimization process of modern diesel engines. The establishing of an automated online calibration demands an accurate optimization method with the ability to handle the increasing complexity of diesel engine concepts and to minimize the calibration time by rapid calculations. Model-based optimziation algorithms used for offline optimization so far do not come up to these requirements. Starting from an advanced design of experiment a knowledge-based expert system has been developed for emulating the decision-making process and the optimization method of an application engineer. The knowledge-based method is exemplarily applied to a stationary operating point.

Previous work has showed that it may be advantageous to use fuels of lower cetane numbers compared to today's diesel fuels in compression ignition engines. The benefits come from the longer ignition delays that these fuels have. There is more time available for the fuel and air to mix before combustion starts which is favourable for achieving low emissions of NOx and smoke though premixing usually leads to higher emissions of CO and unburned hydrocarbons. In the present work, operation of a single-cylinder light-duty compression ignition engine on four different fuels of different octane numbers, in the gasoline boiling range, is compared to running on a diesel fuel. The gasoline fuels have research octane numbers (RON) of 91, 84, 78, and 72. These are compared at a low load/low speed condition (4 bar IMEP / 1200 rpm) in SOI sweeps as well as at a higher load and speeds (10 bar IMEP / 2000 and 3000 rpm) in EGR sweeps.

A 2-step valve train offers a cost effective alternative to fully variable valve trains. Using the small valve lift, which is usually combined with an early intake closing strategy, reduced pumping losses are opposite to decreasing combustion efficiency due to lower charge motion. To work out the trade off between these two effects an extensive coupled CFD investigation is performed. The 1-D engine model delivering the pumping losses is complemented by an empirical combustion model, that relates combustion duration with residual trapped gas content. The model ensures right prediction of fuel economy. Additionally the influence of a small intake valve event on charge motion can also be demonstrated by 3-D in-cylinder flow simulation.

DVCP, a system with continuously adjustable intake and exhaust cam positions, was investigated in terms of residual gas content, intake manifold pressure, pumping losses and fuel economy by means of engine cycle simulation on a 16-valve 4 cylinder naturally aspirated SI engine at part load conditions. Using the simulation results a phasing strategy for part load operation with the primary emphasis on improved fuel consumption has been developed. To verify simulation predictions subsequently, measurements were made at the test rig. It was found that cycle simulation was able to predict properly the behavior of the engine even far away from calibration point. The simulated and measured cam positions for maximum fuel economy matched. Test rig results showed that fuel economy improvement by DVCP is limited by residual gas content tolerance of the engine investigated.