Combustion Efficiency Enhancement Techniques in Modern Diesel Engines

Authors: Manesh Tarachand Khaire

Country: India

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Abstract: Combustion efficiency The ratio of the chemical energy of diesel fuel that is discharged and transformed into useful work is a key lever that is being used to drive modern compression-ignition engines to greater brake thermal efficiency (BTE). Although the highest possible BTE has been demonstrated at the range of 43-45% with heavy-duty diesel engines, research programs and technology demonstrators have indicated that higher gains can be obtained when combustion completeness, phasing of heat-release, and mixing of air and fuel are optimized together through mechanical innovations. The present paper summarizes the PhD-level evidence on the major mechanical methods of improving diesel engines in terms of combustion-efficiency, focusing on fuel-injection and air-management equipment. Topics covered in the review include: (i) high-pressure common-rail injection and enhanced rate-shaping/multiple-injection strategies to enhance atomization, shorten ignition delay, and reduce over-rich zones; (ii) enhancements to architectures (variable geometry turbocharging, two-stage turbocharging with intercooling, and turbo-compounding) to augment excess-air supply and recover exhaust enthalpy; (iii) optimization of combustion-chamber and intake-flow (piston bowl geometry, port design, swirl In all these methods, the key efficiency enhancement tool is the redistribution of heat release to higher levels of effective pressure, and the reduction of incomplete combustion losses (CO, HC, soot precursors) and the occurrence of late-cycle burning. Nevertheless, the review also mentions some major limitations, in particular, the formation of NOx, peak cylinder pressure restrictions, parasitic losses in high-pressure pumping and boosting, and extreme pressures and high-temperature material issues. The general finding is that the most practical gains can be made by system-level integration (injection + air system + chamber design + valve strategy) in line with the high-efficiency demonstration programs which have shown that with well-coordinated mechanical upgrades BTE can now reach or exceed 50% of its under-optimized operating conditions (Dahham et al., 2022; Mohan et al., 2013).

Keywords: diesel combustion efficiency, brake thermal efficiency, high-pressure common rail, multiple injection, turbocharging, variable geometry turbocharger, two-stage boosting, intercooling,

Paper Id: 232876

Published On: 2026-01-09

Published In: Volume 14, Issue 1, January-February 2026

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