From there the air was mixed with the injected fuel and flowed into the engine via the intake valves. The fuel injector used was a Bosch injector rated at 440 cm3/min at a fuel pressure of 3 bar. A Horiba MEXA-720 instrument was used to measure air–fuel ratio (AFR) and NOx emission with an accuracy of 5% for AFR, and 30 ppm, 3% and 5% for NOx emission in range of 0–1000 ppm, 1000–2000 ppm and 2000–3000 ppm, respectively.