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In order to meet future emissions legislation for Diesel engines and reduce their CO2 emissions it is necessary to improve diesel combustion by reducing the emissions it generates, while maintaining high efficiency and low fuel consumption. Advanced injection strategies offer possible ways to improve the trade-offs between NOx, PM and fuel consumption. In particular, use of high EGR levels (⥸ 40%) together with multiple injection strategies provides possibilities to reduce both engine-out NOx and soot emissions. Comparisons of optical engine measurements with CFD simulations enable detailed analysis of such combustion concepts. Thus, CFD simulations are important aids to understanding combustion phenomena, but the models used need to be able to model cases with advanced injection strategies.

Experiments were conducted with a single cylinder heavy duty research engine, based on the geometry of a Volvo Powertrain D12C production engine. For these tests the engine was configured with a low compression ratio, low swirl, common rail fuel injection system and an eight-orifice nozzle. The combustion process was visualized by video via an inserted endoscope. From the resulting images temperatures were evaluated with the two-color method. In addition, the combustion and emission formation were simulated using the multiple flamelet concept implemented in the commercial CFD code STAR-CD. The models used in this paper are considered state-of-the-art. The purpose of this paper is to demonstrate the possibilities offered by combining several methods in the evaluation of novel engine concepts. Therefore, results from the optical measurements, the CFD simulations and global emission experimental data were compared.