A 100 hour (h) engine experiment was conducted to investigate the impact of post-injection strategy on emissions, combustion and lubricant dilution with a common-rail turbocharged direct-injection diesel engine at moderate speed and low load. The fuel was a B20 v/v blend of a soybean methyl ester-based biodiesel and ultra low sulfur diesel. The impacts of post-injection on engine performance and emissions were investigated. The total acid number of the lubricant, the engine mechanical friction mean effective pressure and hydrocarbon components in both the exhaust gases and the used lubricant were analyzed. The variations of engine performance strongly depended on the timing of the post-injection. The key parameter that controlled the combustion process of post-injected fuel at late crank angle (later than 40° after top dead center) was found to be the cylinder temperature at which the post-injected fuel was about to ignite. The bulk cylinder temperature threshold was confirmed to be 1500 K, below which a rapid combustion of injected fuel was not observed. The vaporized components of the post-injected fuel were found to contribute the majority of the significantly increased unburned hydrocarbon emissions with the post-injection strategy. Furthermore, these unburned hydrocarbons were also found to be the primary source for lubricant dilution.

The effect of engine operating conditions on exhaust gas recirculation (EGR) cooler fouling was studied using a 6.4 L V-8 common rail turbodiesel engine. An experimental setup, which included a custom-made shell and tube heat exchanger (EGR cooler) with six surrogate tubes, was designed to control flow variables independently. The engine was operated at 2150 rpm, 203 Nm and 1400 rpm, 81 Nm, representing medium and low load conditions, respectively, and the coolant to the heat exchanger was circulated at 85 °C and 40 °C. Heat exchanger effectiveness and pressure drop was monitored throughout the tests. Deposits from the EGR cooler were collected every 1.5 h for a total of9h, and their microstructure was analyzed using a scanning electron microscope while their chemical composition was analyzed using a pyrolysis GC-MS apparatus, and the elemental weight percentages were obtained using a CHN analyzer. The results of these analyses showed that the effectiveness of the EGR cooler drops rapidly initially and asymptotes in a few hours. The medium load condition had a higher effectiveness loss due to a greater accumulation of deposits inside the EGR cooler, mostly due to increased thermophoresis, and produced smaller and coarse particles. The low load condition had lower effiectiveness loss but produced bigger particles mostly due to excess hydrocarbons. Coolant temperature played a significant role in altering the deposit microstructure and in increasing the amount of condensed hydrocarbons. More deposits were produced for the cold coolant condition, indicating that lower coolant temperature promotes greater hydrocarbon condensation and thermophoresis. These results indicate the complex nature of folding in automotive heat exchangers.

This work explores the role of the ignition quality of a fumigated fuel on combustion phasing and brake thermal efficiency (BTE), which was investigated in a 2.51 turbo charged common rail light-duty diesel engine. Different combinations of dimethyl ether (DME) and propane were fumigated into the intake air and displaced some of the directly injected ultralow sulfur diesel fuel (ULSD) needed to maintain the engine and a constant speed and load. Fumigation of DME and propane significantly increased BTE and reduced brake specific energy consumption (BSEC) compared to the baseline diesel con dition with no fumigation. A mixture of 20% DME with 30% propane provided the maxi mum BTE, with 24% reduction in BSEC, however, at the expense of increasing peak cylinder pressure by 6 bar, which was even higher at greater DME substitutions. Fumi gated DME auto-ignited early, ahead of top dead center (TDC), showing the typical low temperature heat release (LTHR) and high temperature heat release (HTHR) events and propane addition suppressed the early LTHR, shifting more of the DME heat release closer to TDC. Total hydrocarbon (THC) emissions increased, while NOx emissions reduced with increasing fumigation.

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