Key Engineering Materials Vol. 1058

Abstract: The goal of engineers working on internal combustion engines has always been energy efficiency and conservation. In general, diesel engines use less fuel than their petrol counterparts. However, even after a diesel engine rejects approximately two-thirds of the fuel's thermal energy (with one-third going to the coolant and another third to the exhaust), only about one-third is converted into useful power. Theoretically, thermal efficiency would be maximized if the amount of heat rejection is minimized, at least as far as the second law of thermodynamics would allow. low heat rejection (LHR) engines aim to achieve this by minimizing the amount of heat lost to the coolant. Thermal barrier coatings (TBCs) in diesel engines are designed to raise combustion chamber temperature, which in turn offers benefits such as increased power density, fuel efficiency and multi-fuel capability. Specifically, the application of TBCs can lead to an increase in engine power by approximately 7.8% and a reduction in specific fuel consumption by about 15% - 20% compared to uncoated baseline engines, with these effects depending heavily on coating material thickness and fuel blend utilized. Furthermore, the exhaust gas temperature (EGT) can increase by around 27%, with these effects varying based on the coating thickness typically ranging from 150 µm to 300 µm and the type of coating material used. To apply these coatings, engine combustion chamber components such as piston crown, cylinder head, valves and cylinder liners) can be coated using a variety of material deposition techniques. High-Velocity Oxygen Fuel (HVOF), Air Plasma Spray (APS), Electron Beam Physical Vapour Deposition (EBPVD), Electrostatic Spray Assisted Vapour Deposition (ESAVD), and Direct Vapour Deposition (DVD) are examples of material deposition techniques. Plasma spraying is the leading method for applying thermal coating materials to diesel engines components. Due to voids and cracks, it typically exhibits a lamellar microstructure with 10–20% porosity.

Abstract: This study experimentally investigates the cyclic combustion variability of n-pentanol and diesel blends in a four-cylinder CRDI diesel engine at a constant speed of 2000 rpm under varying load and injection timing conditions. Two volumetric blends, DP15 and DP25, were evaluated and directly compared with neat diesel (D100) using in-cylinder pressure data recorded over 100 consecutive cycles. Combustion stability was rigorously assessed using the coefficient of variation of the indicated mean effective pressure (COV_IMEP) and the peak cylinder pressure (COV_Pmax), together with continuous wavelet transform (CWT) analysis of the indicated mean effective pressure signals. The results show that cyclic variability decreases significantly with increasing engine load due to improved in-cylinder temperatures, enhanced fuel and air mixing, and reduced ignition delay. Higher variability was observed at low loads, particularly for the pentanol blends. However, at medium loads, the DP25 blend demonstrated lower coefficient of variation values for IMEP and P_max, indicating more stable combustion compared to both baseline diesel and DP15. The average indicated mean effective pressure (IMEP) and peak pressure (P_max) increased proportionally with load for all fuels, with the pentanol blends demonstrating comparable performance to conventional diesel. Furthermore, injection timing was found to significantly influence the cyclic stability, proving that an optimized injection timing strategy vastly improves overall combustion consistency under specific load conditions. Ultimately, n-pentanol and diesel blends, particularly DP25, exhibit comparable combustion performance and improved stability at medium and high loads, clearly indicating their strong potential as suitable, sustainable alternative fuels for CRDI diesel engines.