A closer look at DiesOtto
Edmunds.com recently took a closer look at the German ingenuity of Mercedes-Benz’s DiesOtto. Imagine the fuel efficiency of a diesel engine minus the rattle and without compromising its power. DiesOtto was first introduced at the 2007 Frankfurt Auto Show and featured in the Mercedes-Benz F 700. The F 700 was intended to be a research vehicle to demonstrate technologies that might be incorporated into future S-Class sedans.
It was termed as DiesOtto to honor Rudolf Diesel, who invented the compression-ignition internal combustion engine, and Nikolaus Otto, who popularized the four-cycle internal combustion engine.
DiesOtto achieves the diesel-like fuel efficiency and great performance through the new combustion strategy called Homogenous Charge Compression Ignition (HCCI). Edmunds.com said that HCCI “combines the technique of spark ignition when the engine is cold or accelerating with the principle of diesel-style auto-ignition under partial loads.”
Until the temperature and pressure rise high enough to ignite the mixture, a lean air-fuel mixture is compressed in the cylinder. HCCI technology then creates a flameless release of energy throughout the entire combustion chamber that completes the combustion process and promotes low temperatures. Fuel efficiency and low-temperature combustion is achieved by the HCCI engine with the help of the lean operation.
In the F700, the Mercedes-Benz DiesOtto engine works with a small gasoline engine, two-stage turbocharging, direct fuel injection, variable valve timing and HCCI.
According to Mercedes Benz, instead of manipulating the cylinder head, variable compression is achieved by physically influencing the crankshaft. DiesOtto’s project leader Günter Karl says, “We can adapt the compression ratio very well to the operating points, so we have good efficiency.” He continues, “Under part load we go as high as possible — higher than spark ignition but lower than diesel. At wide-open throttle we can go lower, so we have no knocking.”
With all the promising effects the DiesOtto has, many are wondering when it will be available in the market. Mercedes-Benz said it will be awhile before it is released since there are many things that need to be done. Günter Karl says, “We have a pressure transducer in each cylinder for closed-loop combustion control. This is absolutely necessary to get good transient behavior between HCCI mode and spark-ignition mode.” He also added that the complexity of the system may need “real physics in the ECU.”
Source: http://www.edmunds.com/insideline/do/Features/articleId=123274