While diesel engines are more efficient than gasoline-powered engines, they have serious emissions problems. A breakthrough in diesel combustion technology may soon lead to cleaner diesel engines.

 

Researchers at Sandia National Laboratories have developed a new strategy, known as "low-temperature combustion" (LTC). LTC works to reduce NOx emissions by recirculating some of the exhaust gases back inside the diesel engine, where they absorb the heat from combustion. Moreover it sprays fuel into the engine cycle earlier to give the fuel more time to mix with air before it burns. This avoids the high temperatures that lead to NOx and the fuel-rich regions that lead to particulate matter (PM).

 

Despite its reductions in NOx and PM emissions, the LTC strategy still releases carbon monoxide (CO) and unburned hydrocarbons (UHC), which are both toxic and result in a loss of fuel efficiency. However, the Combustion Research Facility (CRF) research team in California was able to use a new optical diagnostic technique to observe and understand the chemical processes that result in UHC.

 

The measurements showed that the fuel wasn’t burned to completion due to an over-mixing of fuel near the fuel injector, leading to CO and UHC in the exhaust.

 

This finding allowed combustion researcher, Mark Musculus, and Sandia post-doctoral researcher Jaqueline O'Connor to discover a way to increase fuel concentration. By adding post-injections, which added more fuel in the right area, the zone of complete combustion extends over a larger region. This results in lower UHC and CO emissions while increasing efficiency by making sure less fuel is wasted.