Influence of cooled and uncooled EGR on performance and emissions of 3.0L PCCI diesel engine

This thesis work is the result of a 7 months engine testing and calibration activity performed at the ICEAL (Internal Combustion Engine Advanced Laboratory) inside the Energy Department (DENERG) of Politecnico di Torino. The experimental study was headed by ICE PhD students research team, with the supervision of Prof. Stefano D'Ambrosio, and it involved test bench investigation of an industrial diesel engine provided by FPT Industrial (F1C) with a modified design for PCCI (Premixed Charge Compression Ignition) advanced combustion mode. The aim of this activity is to gain insight on the influence of the utilization of cooled and uncooled EGR strategies on performance and pollutant emissions characteristics of the above-cited engine, with focus on the attainable benefits that hot EGR could produce on the common shortcomings of PCCI combustion. The first chapter addresses conventional combustion in diesel engine, describing its peculiar features as well as the evolution of its conceptual combustion model conceived in recent times. Pollutant emissions formation mechanisms in CI (compression ignition) engines are presented in the second chapter, inside which diesel combustion noise is also introduced. The third chapter is devoted to the central theme of the thesis, i.e., EGR (Exhaust Gas Recirculation), which is typically defined as an engine in-cylinder emissions control technology implemented in diesel engines for nitrogen oxides abatement. The chapter goes through the definition of EGR working principles, its effect on other pollutant emissions, EGR system configurations and the need for EGR cooling, with focus on conventional diesel applications. Then, being this writings concentrated on premixed charge compression ignition (PCCI) combustion strategy, advanced diesel combustion or low temperature combustion (LTC) modes are described in chapter four. Among the various advanced combustion approaches, PCCI could be defined as an early injection low temperature combustion which is achieved by means of an advanced start of injection (SOI) and heavy EGR level, resulting in simultaneous low soot and low NOx pollutant emissions level due to lengthening of the ignition delay and the decrease of in-cylinder peak temperature. The testing campaign have been performed on AVL dynamic engine test bench situated inside Politecnico di Torino ICE advanced laboratory. The engine dyno was equipped with AVL AMAi60 emission analyzer for HC,CO,CO2 and NOx measurement, while fuel consumption and smoke emissions were collected with KMA 4000 and AVL 415S smokemeter, respectively, as described in chapter five. The core of the activity regarded steady state testing on two engine key points: 1400x1.1 (rpm x bar) and 2000x2.3, calibrated in cooled EGR mode during previous experimental studies. Hot EGR configuration was implemented by substituting the EGR cooled with an ad-hoc manufactured steel tube. Tests were executed on both engine EGR layouts by performing EGR quantity sweep varying exhaust back pressure flap opening with EGR valve set on wide-open position. Moreover, the engine was tested by implementing single and double stage injection strategies in either EGR configurations. Finally, results are shown and discussed in terms of intake charge characteristics such as temperature, pressure and relative air fuel ratio, pollutant emissions levels, brake specific fuel consumption, combustion noise and DOC hydrocarbon conversion efficiency.