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Diesel's Dual-Fuel Future

Taking care of emissions in-cylinder, where it belongs

Text By Jason Thompson

One of my goals working here at Diesel Power is to investigate and help spread the latest diesel innovations that'll soon give us all clean, self-sufficient, renewable power. Efficiency, cleanliness, and maximum performance are not at odds with each other, rather they are the results of complete and controlled combustion. Remember the chemical formula for combustion you learned back in middle school? Me neither, but I do remember it was simple-when the reaction gets crazy, that's when you see the NOx and particulate matter (PM). Engine designers have struggled to make the fire inside the engine do what they want, and when they settle on good enough, that's when we get aftertreatments (afterthoughts), smog (PM), acid rain (NOx), ocean acidification (excessive amounts of carbon from underground), and extremely complicated broken-down engines with massive part counts.

Taking Care of Business: In-Cylinder
Led by Dr. Rolf Reitz, researchers at the University of Wisconsin-Madison just broke through the soot-NOx tradeoff barrier, which plagued diesel engines for more than a century. In the past, diesel engines could only control one undesirable emission at a time-but not anymore, thanks to reactivity controlled compression ignition (RCCI). This process involves introducing a premixed, low-reactive fuel (gasoline or ethanol) through an off-the-shelf port injector into the combustion chamber before multiple injections of the reactive fuel (diesel or biodiesel) enter the cylinder. The ratio of gas to diesel changes with engine load and speed. At idle, the engine runs diesel, but as load increases, so does the amount of gasoline. The controlling of the injections, EGR level, boost pressure, intake temperature, and ratios of gas to diesel produce a PCCI-like event. To understand PCCI, read "The Future of the Cummins 6.7L" February '10.

The other contributors to this project include graduate students Reed Hanson, Derek Splitter, and Sage Kokjohn. The diesel engine they tested was the Caterpillar 3401E 2.44 L single cylinder with common-rail injection. According to their data-obtained with an in-cylinder monitoring technique called FTIR Based Optical Diagnostics-the emissions were near zero. For example, NOx was well below .1 grams/kW-hr. At the same time, efficiency increased from 47 percent to 59 percent. With results like these, I'd be willing to trade my aftertreatment equipment for an additional gas tank. It's all about adapting to meet the changing conditions, and with gasoline dominant in the United States-why not use what's available?

Benefits of Controlled Combustion
1. We can retrofit much of the equipment already on the road and in the field with just a common port injector, gas tank, and control module. This could mean my cousin will be able to visit me again in California with his older semi.

2. RCCI requires lower diesel injection pressures (7,250 to 11,603 psi as opposed to more than 30,000 psi), which means lower equipment cost and increased durability.

3. This invention achieves up to 60 percent thermal efficiency (power out divided by fuel in), because the heat release is mostly given off when the piston is in its sweet spot of the power stroke. This means more energy goes into work instead of waste heat, which translates into more fuel economy.

4. No aftertreatment is needed, because emissions are well below current regulations. This will drive down the cost of diesel and improve durability.

5. A B100 (biodiesel) and E98 (ethanol) combination is expected to not only work but also provide the most thermal efficiency.

6. The infrastructure is already in place-all that is needed is a manufacturing partner (licensing@warf.org) to invest the money to prove this technology out. Jason Thompson jason.thompson@sorc.com

By Jason Thompson
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