When a 2.0 diesel in a BMW 1 Series can have CO2 emissions that give it the lowest A rating here and an almost ridiculous €104 annual road tax, it might seem that the technology has reached a zenith.
But there's more than CO2 to diesel emissions, and researchers are hard at work trying to eliminate them in order to get the diesel engine even cleaner.
Researchers in New York have demonstrated a more advanced fuel injection system that can reduce total emissions by 80 percent, and increase overall engine efficiency by 10 percent.
The system is based on making the diesel 'supercritical' before injection into the cylinders. It involves increasing temperatures and pressures of the fuel before burning.
Full prototype engine tests should be underway by the end of next year.
Full technical details are available here in Technology Review.
