Use of Multiple Injections of Increasing Pressure to Reduce Diesel Engine Emissions

Nitrogen oxides and particulates (soot) are two common pollutants that result from the burning of fuel in diesel engines. Cooler engine conditions tend to reduce nitrogen oxide emissions; however these same conditions increase the emission of particulates which do not fully oxidize at lower temperatures. Similarly high engine temperatures oxidize more soot but generate greater amounts of nitrogen oxides. Due to this “nitrogen oxide-soot tradeoff” reducing both types of emissions at once has proven difficult. UW-Madison researchers have developed a multiple fuel injection scheme that should simultaneously reduce both nitrogen oxide and particulate emissions from diesel engines. Instead of injecting a single fuel charge during a combustion cycle several charges are injected. Each charge carries an amount of fuel that when added together equals the single charge and is injected at a higher pressure than the last. Spacing fuel injections into several charges of increasing pressure enlarges the surface area of the soot clouds that are exposed to oxidation. It also maintains more uniform combustion temperatures leading to cooler engine conditions and lower nitrogen oxide emissions. This technique provides higher combustion chamber mixing and greater soot oxidation rates even during the power stroke when mixing rates are reduced due to piston expansion. Technology Applications: Diesel engines


1) Results in lower particulate and nitrogen oxide emissions than single injection schemes using similar timing and fuel volume 2) Provides an innovative way for the diesel engine industry to meet new tougher emission standards 3) Achieves particulate control within the combustion chamber using a straightforward modification of existing hardware 4) Eliminates need for cumbersome and expensive particulate traps 5) May be used with exhaust gas re-circulation (EGR) to further reduce nitrogen oxide emissions 6) May result in better fuel economy

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