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AVL's research work on advanced combustion systems for four-stroke gasoline engines has revealed a strong influence of charge motion and mixture preparation on engine performance, especially exhaust emissions and fuel economy. This paper presents the effects of mixture preparation and charge motion revealed in studies of AVL High Compression Fast Burn (HCFB) combustion systems. Major combustion parameters were investigated and optimized. Control of charge stratification emerged as one of the key elements of advanced combustion systems for both two-valve and four-valve engine configurations. Consequently, measures for charge stratification control are also presented.

The AVL-HCLB ( High Compression Lean Burn) Combustion System development work, carried out on a single cylinder research engine and a first generation 4IL engines for passenger car application, has led to intensified R&D acitivity on soma particular features of the AVL System to enable its full fuel economy potential to be realized -while still conforming with current and proposed exhaust emission standards. It is shown that, compared with cast iron, aluminum is the better cylinder head material also for HCLB engines. A Variable Swirl Intake Port developed at AVL has enabled WOT ( Wide Open Throttle) performance and upper part load NOx emissions characteristics to be improved. By means of an air flow/fuel flow and engine speed governed engine management system, the upper part load BSFC and NOX emission trade off of the HCLB-englnes has been optimized. An EGR-valve with a non linear flow characteristic has proven to be an important contributing factor in this respect.

The market-driven need to further improve the fuel economy of passenger cars, while meeting current and anticipated future emission regulations, represents a challenging target for today's engine research and engineering. Based on the results of intensive spark ignited engine combustion system research work. AVL has developed a development strategy that is responsive to both the require-rents of expected limitations in worldwide energy supply and to current and proposed exhaust emission standards. This strategy is presented in this paper. Supported by single cylinder research engine investigations into the combustion phenomena of lean homogeneous mixtures, multi-cylinder engine development has been carried out on two in-line (IL) four cylinder engines, of 1.6 and 2.3 litre displacement, respectively.