Modern internal combustion engines are reliable as they feature little to no critical engine faulty if they are properly maintained. Reliability of the engine can be estimated by considering different loads on the engine parts while operating in predicted operating regimes. These operating regimes are obtained by using conventional combustion concepts that are widely applied in current engine generations. If we wish to upgrade an existing combustion concept to advanced combustion concept in combination with an alternative fuel, the limits for reliability have to be reassessed. In this thesis a compression ignition engine that that operates on Reactivity Controlled Compression Ignition (RCCI concept) while using hydrotreated vegetable oil (HVO) and natural gas (NG) as bio-alternative to existing diesel fuel is researched. The criterion for reliable operation is evaluated in different operating points, where each point has a different share of recirculated exhaust gases, from 0% to 40% and different shares of natural gas (NG), from 95% to 55%. The results of the experiment suggest that when using a proportion of EGR higher than 30% or proportion of NG higher than 57%, parameters for evaluating the operation reliability (COVIMEP in COVpmax) move away from acceptable values. Introduction of RCCI combustion concept in existing internal combustion engines thus requires implementation of new limits to operational regime to maintain reliability.
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