Found another article that claims 6.44 decrease in fuel consumption.
The obtained results have been compared with conventional gasoline engine in terms of performance and NO, CO, CO2, HC emissions. The results of theoretical combustion model agree with experimental data quite well. In the experimental results, it is seen that the engine torque and the effective power increase up to 4.65% at 3200 rpm, specific fuel consumption reduces up to 6.44% at 2000 rpm. There is 40% average reduction in NO emissions at 2800 rpm and it is 31.5% in HC emissions at 2000 rpm.
The effects of electronic controlled steam injection on spark ignition engine
It is a paid publication that I have not bought.