A method for controlling regeneration of a lean NOx trap includes estimating an accumulated NOx in the lean NOx trap; determining whether the estimated NOx exceeds a first threshold value or a second threshold value; estimating the temperature of the lean NOx trap; determining whether the estimated temperature exceeds a threshold temperature; determining a desired air-fuel ratio for initiating a regeneration event, the desired air-fuel ratio being determined based upon the estimated NOx and the estimated temperature of the lean NOx trap; hastening the occurrence of a regeneration event when the estimated NOx exceeds the first threshold value through active control of engine operating regimes; and initiating a regeneration event when the estimated NOx exceeds the second threshold value or when the estimated temperature exceeds the threshold temperature by forcing homogenous operation of the engine at the desired air-fuel ratio.