Diesel-water microemulsions as alternative fuels in diesel engines display at consumption-neutral to consumption-reducing motor conditions a substantial reduction of both nitrous oxide and particulate matter, i.e., the problematic soot-NOx trade-off is broken. For adjusting the optimal water fraction an on-injector blending, i.e., the emulsion formation right before the injector is suggested. Thus, at load change the new diesel-water mixture is ready, while the water may be recovered from the exhaust gas. This unused water injection would be relatively easy to implement and would lead to a substantial relief for the environment.