The fast reduction of fossil fuels is making it imperative to search for renewable fuels to be used in the IC engines. The use of alcohols as fuel in the CI engines either directly or as blends of diesel requires some modification of the engine operating parameters to minimize the emissions without affecting the performance. Among the different operating parameters, Compression ratio (CR) and Fuel injection pressure (FIP) strongly affect the performance characteristics of the CI engine. In this paper, the influence of CR and FIP on the combustion, performance and emission characteristics of a CI engine fuelled with butanol/diesel (B/D) blends is presented. Experiments were performed on a Variable Compression Ratio (VCR) engine by varying the CR (CRs of 14:1, 15:1, 16:1, 17.5:1and 18:1) and the FIP (FIP of 200 bar, 220 bar, 240 bar, 260 bar and 280 bar) with three different (B/D) blends (butanol fraction of 0%, 20% and 40% by volume). The experimental outcomes showed that for all the (B/D) blends, with increase in the CR from 14 to 18, the in-cylinder pressure, net heat release (NHR) and Brake Thermal Efficiency (BTE) increased. The soot, CO and UBHC emissions decreased, while the NOx emissions increased with increase in the CR from 14 to 18. Similarly, the effect of FIP was to increase the in-cylinder pressure, net heat release (NHR), BTE and the NOx, and reduce the soot CO and UBHC emissions. The effect of CR and FIP for different butanol/diesel blends was experimentally evaluated. There existed an optimum value of FIP for each test fuel, corresponding to which the best performance was obtained. For the Bu00 (diesel) and Bu20 test fuels this optimum value was 260 bar, whereas for the Bu40 test fuel, it was 240 bar. At the higher CR of 18, Bu40 gave the best performance with BTE of 30.14%.
