In this paper, two kinds of novel boosting pressure approaches, steam turbocharging and steam-assisted turbocharging, have been proposed. And both are based on the principle of internal combustion (IC) engine exhaust gas energy recovery. In order to demonstrate the advantages of the two types of new turbocharging concepts, a comparative study among exhaust turbocharging, steam turbocharging and steam-assisted turbocharging was conducted on a passenger car gasoline engine, and the effects of various boosting pressure approaches on IC engine performances as well as turbocharging system energy flow were analyzed. The results show that, steam turbocharging can achieve the target intake pressure in the entire IC engine speed range, while steam-assisted turbocharging can improve IC engine intake pressure at the low-speed operating conditions; the energy saving potentials from high to low follow the subsequence of steam turbocharging, steam-assisted turbocharging and exhaust turbocharging; with the increasing of IC engine speed, the exhaust gas energy recovery efficiency of steam turbocharging system decreases and its maximum value is 6.5%, while the exhaust gas energy recovery efficiency of steam-assisted turbocharging and exhaust turbocharging first increases and then decreases. (C) 2013 Elsevier Ltd. All rights reserved.