This experimental investigation aimed to depict the effects of varying loads at various compression ratios with thumba methyl esters in different proportions as fuel on a variable compression ratio diesel engine. Series of tests were conducted on a single cylinder, 3.6 kW, water cooled, variable compression ratio, stationary diesel engine, as per the full factorial design to measure the performance and emission characteristics. The engine load, compression ratio and blending ratio for citrullus colocynthis (thumba oil) based diesel were taken as input parameters and their effects on engine performance and emissions characteristics such as BTE, BSFC, HC, NOx & CO were investigated experimentally and analytically. Experimental data was analysed and modelled using the full factorial design in three different stages to achieve the optimum results for performance and emission characteristics. For each stage, second order and third order estimate models were developed and were checked for assumptions of Analysis of Variance i.e. normality & homogeneity of data. The optimum performance & emission characteristics were observed with 20% thumba-diesel blend, at a compression ratio of 18 at maximum load. It was found that the optimum values of BSFC, BTE, HC, CO & NOx was 0.456 kg/kWh, 19.725%, 38.432 ppm, 0.026% and 348.744 ppm respectively at load of 10 kg, CR of 18, and blend percentage of 20. A good agreement between experimental results and predication results depicts that the developed models can be used with competence to optimize similar type diesel engine parameters using citrullus colocynthis (thumba oil) blend without engine modification. (C) 2019 Elsevier Ltd. All rights reserved.