<div class="section abstract"><div class="htmlview paragraph">An experimental study was conducted on a Ricardo Hydra single-cylinder light-duty diesel research engine. Start of Injection (SOI) timing sweeps from -350 deg aTDC to -210 deg aTDC were performed on a total number of five pistons including two baseline metal pistons and three coated pistons to investigate the effects of thick thermal barrier coatings (TBCs) on the efficiency and emissions of low-temperature combustion (LTC). A fuel with a high latent heat of vaporization, wet ethanol, was chosen to eliminate the undesired effects of thick TBCs on volumetric efficiency. Additionally, the higher surface temperatures of the TBCs can be used to help vaporize the high heat of vaporization fuel and avoid excessive wall wetting. A specialized injector with a 60° included angle was used to target the fuel spray at the surface of the coated piston. Throughout the experiments, the equivalence ratio, ϕ, was maintained constant at 0.4; the combustion phasing was consistently matched at 6.8 ± 0.4 deg aTDC. It can be concluded that the thick TBC cases achieved 1 to 2 percentage points improvement in combustion efficiency, and generally, a ~2 percentage points increase in indicated engine efficiency. It is also noticed that applying a dense top sealing layer to the TBC further improves the UHC emissions compared to the TBC coated piston with an unsealed surface. From the heat release analysis, it can be concluded that the TBCs have no significant impact on the heat release process and knock intensity while matching the combustion phasing; however, it reduces the intake temperature requirement by up to 20 K. The exhaust gas temperatures were expected to increase for the TBC cases, but the expected increase in exhaust temperature was not conclusive from the results observed in this study.</div></div>
<div class="section abstract"><div class="htmlview paragraph">In military applications, diesel engines are required to achieve high power outputs and therefore must operate at high loads. This high load operation leads to high piston component temperatures and heat rejection rates limiting the packaged power density of the powertrain. To help predict and understand these constraints, as well as their effects on performance, a thermodynamic engine model coupled to a finite element heat conduction solver is proposed and validated in this work. The finite element solver is used to calculate crank angle resolved, spatially averaged piston temperatures from in-cylinder heat transfer calculations. The calculated piston temperatures refine the heat transfer predictions as well requiring iteration between the thermodynamic model and finite element solver. Both the thermodynamics and the piston temperature predictions are validated against experimental data obtained from a heavy-duty single cylinder research engine equipped with a wireless telemetry system and piston surface thermocouples to measure piston surface temperatures. The piston backside conditions are critical to the performance of the temperature solver, therefore the tuning of piston backside conditions to match experimental data is considered and assessed. The validated model is then used to analyze the performance of the heat transfer correlations developed by Woschni and Hohenberg. The piston temperatures predicted by each of the correlations are compared to those measured in the experiment both in terms of the piston temperature swing and its sensitivity to injection timing. Finally, the capabilities of the coupled model are demonstrated by analyzing the effects of engine geometry on engine performance relative to critical limitations for military engines.</div></div>
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