Methanol has been injected at the intake port with heated inlet air in a diesel engine. In the meantime, the Taguchi methodology was adopted to estimate the optimal methanol-energy-share ratio, methanol injection timing, and inlet air temperature. The injection timing and the quantity of methanol were controlled by an ECU (electronic control unit) on an electronic injector. The inlet air temperature was raised by an electric heater. The authors estimate the optimal combination of factors for larger brake thermal efficiency (eta(b)), smaller smoke, NOX, HC and CO pollutant emissions for different loads. In addition, net heat release rate is obtained by the measured in-cylinder pressure data. Comparison of between the optimal combination of factors and original conventional diesel engine is made by eta(b), smoke, NOX, HC, CO and net heat release rate. Carrying out the confirmation tests can show that the predictions of the Taguchi methodology agree with the confirmation tests in the 95% confidence level. For the optimum combinations of factors, the maximum decrease percentage is 41.5% for smoke emission, 61.7% for NOX, 8.6% for HC emission, and 32.4% for CO emission. (C) 2017 Elsevier Ltd. All rights reserved.