Effect of Neem Methyl Ester (NME) Biodiesel Blends on Combustion-Induced Vibration, Performance, and Emission Characteristics of a Variable Compression Ratio Direct-Injection Diesel Engine

Abstract

The steady depletion of fossil-fuel reserves and increasingly stringent emission legislation have driven sustained interest in renewable, oxygenated alternatives to mineral diesel. This paper reports a systematic experimental investigation into the combustion-induced vibration, performance and emission behaviour of a single-cylinder, four-stroke, water-cooled variable compression ratio (VCR) direct-injection diesel engine fuelled with Neem Methyl Ester (NME), its diesel blends (B10, B20, B30, B40) and diesel-NME-methanol ternary blends (B1, B2). Vibration was acquired along three mutually perpendicular axes using a triaxial accelerometer, while in-cylinder pressure was captured with a piezoelectric transducer synchronised to a TDC crank encoder. Tests were conducted at 1500 rpm across compression ratios of 14, 15, 16 and 17.5, from no-load to full-load. The results show that NME consistently reduces combustion-induced vibration relative to diesel, with vertical-direction reductions of up to 42.2% at full load, alongside improved HC and CO emissions but marginally higher smoke opacity and brake specific fuel consumption. Among the blends, B10 and B1 delivered the best compromise between low vibration, low emissions and acceptable performance, supporting their use as viable near-term substitutes for diesel in unmodified compression ignition engines.