A conceptual analysis of the mechanism of the Miller cycle for reducing NOx emissions is presented. Two versions of selected Miller cycle (1 and 2) were designed and realized on a Rover "K" series 16-valve twin-camshaft petrol engine. The test results showed that the application of the Miller cycle could reduce the NOx emissions from the petrol engine. For Miller cycle 1, the least reduction rate of NOx emission was 8% with an engine-power-loss of 1% at the engine's full-load, compared with that of standard Otto cycle. For Miller cycle 2, the least reduction rate of NO, emission was 46% with an engine-power-loss of 13% at the engine's full-load, compared with that of standard Otto cycle. (C) 2007 Elsevier Ltd. All rights reserved.