Fuel efficiency is the key buying factor in the non-road diesel engine market, because the engine mainly operates in the high torque region and consumes relatively large amount of fuel in a short term. A compression ratio of diesel engine is deeply related to a thermal efficiency and it is one of the key design parameter influencing on the fuel efficiency. In this paper, the new approach to select compression ratio is described and the design constrains such as in-cylinder max allowable pressure, max allowable temperature at turbine front end and max allowable temperature at compressor back end were considered. The base engine is 3.4 liter non-road diesel engine without EGR (Exhaust Gas Recirculation) system for Stage V emission standards and is originated from the same engine system with EGR system to meet Tier 4 Final emission standards. Its official compression ratio is 17.0. The purpose of this study is to select an optimal compression ratio for non-road diesel engine system with non-EGR system to meet Stage V emission standards. The methodology to be presented in this study is based on the 1-D engine performance simulations, the 3-D CFD (Computational Fluid Dynamics) combustion simulations, and the engine bench test. In these simulations, a compression ratio and a SOI (Start of Injection) were considered for sweeping parameters. With analyzing the results of parameter studies and engine design constraints, an optimal compression ratio is found to be 18.0. As a result of many engine bench tests, a fuel consumption has been improved by 1.5% with new piston bowl of which compression ratio is 18.0, meeting Stage V emission standards.

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