Sounds great, it's just a pity that photosynthesis occurs above the ground. Despite all the claims there is a serious lack of scientific studies and actual evidence, the only study I've been able to find concludes:
There may be some short term benefits as the acids present in the exhaust gasses react with nutrients bound up in the soil but in the long term these reserves will become depleted. Some proponents are reporting drops in soil pH. While the website promoting this system looks quite flashy it apears very short on providing actual information on how it works or any data to support their claims. I don't think I'll be buying it.
The ANCOVA showed that the injection of exhaust did not improve or compromise crop production relative to the control. However, injecting exhaust while simultaneously applying fertiliser did initially reduce crop growth. In this season and on this soil, the crop was unresponsive to the application of fertiliser except for a small, significant increase in grain protein.