Researchers from the Center for Information Technology Research in the Interest of Society (CITRIS) are developing more efficient engines for cars. They are specifically working on Homogeneous Charge Compression Ignited (HCCI) engines. An HCCI engine 'combines the efficiency and versatility of diesel engines with the cleanliness of spark-ignition engines.' For example, an HCCI engine uses 15% less fuel than gas engines and emit only 30% of the NOx of a typical diesel engine. The big problem with HCCI engines is that they are very sensitive to temperature variations. CITRIS researchers are developing 'sensors and controllers that will keep temperatures constant throughout the engine or compensate for temperature differentials by modifying pressure ratios within the cylinders.' They also want to use wireless communication connections between cars and fuel pumps. But read more...
You can see above a diagram showing how diesel, petrol and HCCI engines work. As the caption is part of the diagram, I'm including it here for clarity. "In HCCI and petrol engines, the fuel and air are mixed before combustion, preventing the soot emissions of diesel engines. Only HCCI engines have multiple ignition points throughout the chamber. This plus their lean burn keeps temperature low, preventing formation of nitrogen oxides (NOx)." (Credit: UC Berkeley) Here is a link to a larger version of this diagram. And here are two other links at UC Berkeley and at Wikipedia about HCCI engines.
Below are some quotes from CITRIS researchers, which all belong to UC Berkeley, California.
For example, Hunter Mack, a member of the UC Berkeley Combustion Analysis Laboratory, said that "temperature variations can make HCCI engines a nightmare on wheels." The CITRIS newsletter adds that "the way that HCCI engines work is to premix fuel the way that a spark engine does, but then compression-ignite the fuel in the manner of a diesel engine. It is the compression ignition that gives them their high efficiency but also leaves them vulnerable to temperature variations across the cylinders. The ignition occurs when pressure reaches a certain point within a cylinder, and that point is achieved sooner if temperatures are higher. So, if a load changes on the engine and the coolant gets hotter as it moves through, then the coolant will not thoroughly cool some cylinders, which will cause the ignitions to fall out of synch and misfire."
Another UC Berkeley engineer, Professor Robert Dibble, said that "these HCCI engines have a lot going for them. They are clean, efficient, and can run on almost anything -- including a variety of biofuels, diesel, or gasoline-like mixtures -- but before we can really exploit them, we have to solve this [temperature] problem." The CITRIS newsletter adds that "the HCCI engines need to have control, which means they must be properly sensed, evaluated, and then actuated, according to Dibble. In order for these engines to be practical, as their load becomes uneven, each HCCI cylinder has to be monitored and adjusted constantly."
While these researchers are working hard to improve HCCI engines efficiency, Professor Albert Pisano "is developing wireless sensors that will make the essential communication step possible. Some may be microphones, others will sense temperature or pressure, but many times a second they will report on conditions from inside the cylinders. Once the engine knows that some cylinders have to be a little hotter or cooler or slower or faster to fire in synch with their neighbors, it will take steps to re-adjust them."
Another group is working on wireless communications. "Dibble and UC Berkeley engineering Professor Van Carey have been talking to oil companies about establishing and taking advantage of wireless communication links between the vehicle and the fuel pump. 'The car can pull up to the station and tell the pump that its efficiency is low, for instance,' says Carey. 'And the pump responds, perhaps by determining that the engine is having incomplete combustion and needs a higher octane fuel. The pump could also recommend the cheapest, best-running biofuel cocktail available at that time.' 'Fuel does not usually have much brand appeal,' says Mack. 'But these fuels would be mixed specifically for your car; the microbrews of gasoline.'"
Of course, some of these sensors could be adapted to be used by other kinds of cars.
Sources: Gordy Slack, CITRIS Newsletter, June 10, 2008; and various websites
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