Search Results

The simulation activity for the piston bowl development in a low compression ratio (CR) high-performance diesel engine is described, starting from the calibration of a 3-D CFD commercial code by pressure-based combustion diagnostics data. Calibration was made for the baseline engine built by GMPT-E, matching experimental pressure traces and heat release rates derived from these through the diagnostic tool. Measured pollutant emissions were also applied for calibration at this stage. The engine was susceptible to modifications, according to the outcomes of combined simulation and experimental investigations. The validated CFD model was used for the screening of three new piston bowls featuring a reduced compression ratio. The 3-D code has been integrated with a robustly calibrated 1-D hydraulic model for the injection system simulation and with a 1-D fluidynamic tool for modeling engine flow processes external to the cylinder to provide quite accurate boundary conditions.

The development trends of advanced automobile engines towards high power-to-volume and power-to-mass ratios are partially in contradiction with the requirements regarding drastically reduced fuel consumption and pollutant emission. The development way of the engine between customer acceptance and limitations by law is mainly determined by the optimization of scavenging, mixture formation and combustion characteristics, as functional base for the engine design. The paper presents a new direct injection concept and its optimization correlated with the scavenging process. The process simulation - as a base for the engine development - was carried out using concomitantly two CFD codes - FIRE and VECTIS. The main optimization parameters were the combustion chamber design, the injector location, the spray characteristics, the spark location, the injection timing and duration.

The injection rate modulation and the spray characteristics are determining factors for the quality of mixture formation when applying GDI. Their variation with load and speed is a basic criterion for the adaptability of a type of injection system to an engine with known requirements. The increased interest for the utilization of regenerative fuels - such as methanol obtained from biomass - as well as the success of previous utilization scenarios of variable gasoline/methanol mixture using manifold injection formed the base of the present analysis: the paper describes the results concerning injection performances and spray characteristics when using gasoline/methanol mixtures with different ratios in a direct injection system with high pressure modulation. The results are compared for different parameters of the injection systems as follows: injection volume, injector opening pressure, needle lift, pintle/seat geometry.

The actual trends in development and series application of mixture formation techniques for SI engines converge irrevocably to a process after scavenging, by direct injection, the reason being the higher thermal efficiency in a wide operation range of the engine, leading to substantially lower bsfc and pollutant emission. After numerous and successful research projects of direct injection for two-stroke engines, the most of series applications are being introduced for four-stroke automotive engines. A main reason for this profitable way consists in the better fluid dynamic conditions and in the longer time for mixture formation in the case of the four-stroke process.

The paper presents the results of a down-sizing concept implicating gasoline direct injection, which is applied to a four-stroke four-valve SI engine with a displacement of 500 ccm per cylinder. The typical features of a down sized engine such as a high level of engine speed, high power density at low fuel consumption and a low level of pollutant emission form the main targets of this study. Numerical models of the process stages have been developed in 1D and 3D CFD codes. The accurateness of the models has been proved using experimental results. The main work consisted on the application of a direct injection system to the engine. The compact engine design and the high compression ratio have been maintained resulting in a combustion chamber design without any cavities or bowls. To obtain accurate results, the simulation work has been carried out using two different CFD-codes (FIRE and VECTIS); the results have been analyzed and compared.

The future development of two-stroke engines will be conditioned by the drastic reduction of pollutant emission, especially of hydrocarbon. This goal is not achievable only by scavenging improvement, rather a new quality of mixture formation using direct injection is imposed. However, the internal mixture formation in a large range of speed and load, considering the scavenge flow particularities of two-stroke engines as well, appears as an extremely complex process. Thereby a numerical simulation is in this case very effective for the adaptation of a direct injection method at the engine. The paper presents a concept for modeling and optimization of the mixture formation process within a high-speed two-stroke engine with liquid fuel injection system. The injection system generates a pressure pulse which is not dependent on the engine speed.