In the present study, the effects of water injection (WI) into intake air on the performance and exhaust emissions were experimentally investigated in a Renault K9K 700 type turbocharged common-rail DI automotive diesel engine. Experiments were performed at different loads and engine speeds, with various water ratios (WRs). The water was injected into intake air by a carburetor, which main nozzle section is adjustable, at approximately 2%, 4%, 6%, 8% and 10% (by vol.) water ratios. It was determined that, WI into intake air at specified ratios decreases significantly smoke index K and NOx emission and improves somewhat the engine performance. Smoke index K decreases by increasing of WRs at 2000, 2500 and 3000 rpm. Its maximum reduction ratio was obtained as 41.75% for 11.71% WR at 3000 rpm. At chosen loads and engine speeds, as WRs increases, NOx emission decreases. More significant reduction of NOx has been obtained after 6% WR. For full load (149 N m) at 2500 rpm, maximum decrement of NOx emission was attained as 12.489% for 9.400% WR. Water addition results insignificant effect on brake specific fuel consumption (bsfc) at 2000, 2500 and 3000 rpm. At these engine speeds bsfc takes values close to the neat diesel fuel (NDF) or increases slightly. However, bsfc decreases approximately 4% with water addition for selected loads at 3500 rpm. WI does not show any significant change in-cylinder pressure and indicated power. (C) 2012 Elsevier Ltd. All rights reserved.