In this study, the effects of engine-operating conditions on the combustion characteristics and emissions of an indirect injection (IDI) diesel engine have been experimentally investigated. The engine tests were conducted on 20, 30, and 40 N m constant loads and at full load condition. The experimental results show that the maximum cylinder gas pressures (P-max) increased with an increasing engine speed and load. The location of the maximum cylinder gas pressure closed to top dead center (TDC) at high engine load. The starts of combustion (SOC) points closed to TDC at high engine speeds. The ignition delay (ID) slightly decreased with the increase of the engine loads, and it increased with an increasing engine speed. However, as the total combustion duration (TC) increased with an increasing engine load, it decreased with high engine speeds. The exhaust emissions, such as nitrogen oxides (NOx), smoke opacity, unburned hydrocarbon (HC), and carbon monoxide (CO), were also discussed for different operating conditions.