The purpose of this study is to examine the reactivity controlled compression ignition (RCCI) engine combustion characteristics using jatropha oil blended with diesel as the high reactivity and n-amyl alcohol as the low reactivity fuel in various proportions by volume. Response surface methodology (RSM) is adopted to forecast the operating parameters such as fuel injection timing (FIT), fuel injection pressure (FIP), and engine load. This ideal model is used to obtain the maximum combustion pressure and reduce the emission of unburnt hydrocarbon (HC) and oxides of nitrogen (NOx) for different fuel blends. For an RCCI engine fueled with B20/1-pentanol fuel, the impact of various factors such as engine load, FIT, and FIP are analyzed based on an L20 orthogonal array. With the help of the results obtained from experiments, various models were developed and validated. The ideal engine parameters found out were 71% of engine load, FIP of 400 bar, and 27 °bTDC, and under this configuration, the maximum cylinder pressure is achieved. The ternary fuel develops higher maximum pressures of combustion than that of pure diesel at higher loading conditions, pressures of fuel injection, and advanced injection timings. At lower loading conditions, fuel injection pressures and ignition delay are noticed, whereas peak pressure decreases. Also, analysis of variance (ANOVA), a statistically valid test, is used to develop a regression model, and the test results indicate that the regression model is appropriate for the following R2 values obtained.