Control Strategies on HCCI Engine Performance and Emission characteristics by Combined Effect of Exhaust Gas Recirculation with Blend of Biodiesel and N-Heptane

Abstract

The usage of Tamanu methyl ester (TME) in a conventional CI engine produces more NOx emission because of in-built oxygen content in biodiesel. Simultaneous reduction of NOx and smoke is a really difficult way in a conventional CI engine. The usage of biodiesel in the HCCI engine would be a better way to reduce smoke and NOx emission due to the homogenous mixture rather than heterogeneous combustion and lower in-cylinder temperature. In this study, the experimental analysis was carried out on a single-cylinder engine operated in HCCI mode. The test fuels used for this experiment are TME 90% + n-heptane 10% (TME90nH10), TME 80% + n-heptane 20% (TME80nH20), TME 70% + n-heptane 30% (TME70nH30), and TME 60% + n-heptane 40% (TME60nH40). The test results noticed that brake thermal efficiency (BTE) of TME70nH30 showed higher when compared to neat TME, diesel, and other blends. The CO, HC, and smoke emission were decreased by 3.1%, 6.5%, and 9.2%, respectively, for a blend TME60nH40 when compared to TME70nH30. The smoke and UBHC emission of TME60nH40 was 23.5% and 26.4% lower than the HCCI mode of operation in diesel fuel. When n-heptane concentration increases beyond 40% in the blend, the performance characteristics of the engine started to decrease due to the high cetane rate of n-heptane which leads to shortening the span of the autoignition period that results in too advanced combustion. Based on emission characteristics of the engine, TME60nH40 was chosen to be the best blend and further study was carried out using TME60nH40 at different exhaust gas recirculation (EGR) percentages. The engine was operated with TME60nH40 with different EGR percentages of 5, 10, and 15. With the increase in the percentage of EGR increases the CO and UBHC emissions but on the other side, NOx emission was drastically decreased.

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