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Today, a number of simulation codes are available for pre-designing gas exchange systems of IC engines with good accuracy (e.g. PROMO, WAVE, GT-Power). However, optimizing such systems still requires numerous time consuming and inefficient trial and error runs. Also, accounting for constraints as size, volume, peak combustion pressure etc. multiplies the necessary efforts additionally. Hence there is a strong need for efficient procedures for finding optimum designs automatically and reliably. To automatically find the global optimum design parameters under a given set of real constraints of a practical case, a multi-membered evolution-strategy based optimization code was developed. The code which efficiently finds the true optimum dimensions of gas exchange systems (duct lengths, duct diameters, volumes) of an IC engine. The code can be readily generalized, and adapted to arbitrary optimization problems.

1 A recent breakthrough in understanding the origin of ion signals from operating combustion engines [12] led to a new approach in integrating advanced ion current sensing into a compact ignition system. Thus it is now possible to continuously monitor mixture, ignition and combustion properties through online ion current recordings via a novel AC technique. In this paper this AC technique is compared to the standard DC technique and its known drawbacks: expensive high voltage components, sensitivity to plug fouling and expensive electronics. The AC technique is based on the specific properties of the electrical field of spark plugs being characterized by a point source with an extreme inhomogeneity of the electrical field due to the small center electrode. This causes a distinct diode characteristic of the ion signal: very low signals for negative voltages and high signals for positive ion sensing voltages, respectively.

For studying the effects of injection system properties and combustion chamber conditions on the penetration lengths of both the liquid and the vapor phase of fuel injectors in Diesel engines, a holistic injection model was developed, combining hydraulic and spray modeling into one integrated simulation tool. The hydraulic system is modeled by using ISIS (Interactive Simulation of Interdisciplinary Systems), a one dimensional in–house code simulating the fuel flow through hydraulic systems. The computed outflow conditions at the nozzle exit, e.g. the dynamic flow rate and the corresponding fuel pressure, are used to link the hydraulic model to a quasi–dimensional spray model. The quasi–dimensional spray model uses semi–empirical 1D correlation functions to calculate spray angle, droplet history and droplet motion as well as penetration lengths of the liquid and the vapor phases. For incorporating droplet vaporization, a single droplet approach has been used.

2-dimensional time resolved (200 frames/s) flow field measurements have been made in a transparent SI square piston engine using a movie version of particle image velocimetry (PIV). To this end the beam of a copper vapor laser was formed into a light sheet and was double pulsed with a pulse separation of 50 μs at a repetition rate of 200 Hz. A rotating drum camera was used to record the Mie-scattered signals from seeding particles. The circumferential velocity of the drum of the camera causes an image shifting of the two exposures taken with a double pulse. By proper adaption of drum and engine speed, a series of up to 70 double pulsed images per individual engine cycle may be recorded on film. This film data may be evaluated uniquely with respect to both magnitude and direction of individual flow vectors in the flow field.

The fluorescence characteristics of different carbonyl compounds were investigated in a pressurized bomb using an excimer laser (308 nm) for excitation. The partial pressure of the carbonyl compounds and air was varied between 0 - saturation pressure and 0 - 5 bar, respectively. The fluorescence signal of different ketones increased almost linearly with vapour pressure. It was found to be almost independent of air pressure indicating only a weak quenching influence of oxygen. Ethylmethylketone (EMK) has a boiling temperature and vapour pressure similar to gasoline. Therefore, the applicability of EMK for measuring 2-D fuel distributions in a combustion chamber was tested in a transparent SI square piston engine. EMK was injected into the intake manifold by a conventional injector for studying the fuel/air mixing during the intake and compression stroke at 1.000 rpm. From the 2-D fluorescence signals 2-D air/fuel ratios were calculated using calibration data from bomb experiments.

A detailed, one-dimensional, time dependend model is presented, describing flame kernel development in spark ignition engines which explicitely accounts for all fundamental properties of the ignition system (supplied electrical energy and power, discharge mode, energy transfer efficiency to spark plasma, plasma temperature distribution, gap width, heat losses to electrodes and chamber walls), of the combustible mixture (pressure, temperature, equivalence ratio, residual gas fraction, laminar burning velocity, type of fuel) and of the flow field (mean flow velocity, turbulence intensity, strain, characteristic time and length scales, flame holder effects). The model is based on the strained flamelet model and predicts kernel growth consistently under virtual all relevant physical/chemical conditions. Model predictions have been verified in extensive studies in an optical engine over a wide range of physical/chemical parameters using advanced optical and laser optical diagnostics.

The nature of autoignition and knocking is investigated experimentally and theoretically in an optical engine by high speed direct light photography and laser schlieren filming. Special emphasis is devoted experimentally and theoretically to the role of exothermic centres in the end-gas in initiating knocking combustion and subsequent knock damage to the combustion chamber walls. The optical engine is a modified single cylinder ported two stroke engine equipped with a large head window for unlimited access to both the entire combustion chamber and the ring crevice region. In some experiments the formation of exothermic centres was stimulated by microscopic aluminium particles that deposited on the mirrored piston surface. The data are analysed by numerically modelling the transition from normal combustion to autoignition with a simplified 2D-code.