Mercedes-Benz introduces the DiesOtto - German for HCCI

Posted Jul 25th 2007 12:03PM by Sam Abuelsamid
The very first practical automobile was the 1886 Benz Motorwagen created in Stuttgart by Karl Benz. That first car was powered by a small gasoline fueled engine that ran on a four-stroke cycle developed by fellow German Karl Otto. Later another German, Rudolph Diesel, developed the compression ignition engine that would end up carrying his name and the company that evolved from the work of Karl Benz and Gottlieb Daimler would be the first to use the type in production in the 1920s.

Now in 2007 Mercedes-Benz is working on bringing the two staple four-stroke engine types of the twentieth century together under the name DiesOtto combining the aspects of the Diesel and Otto cycles. The Mercedes engineers have created a 1.8L gasoline fueled four-cylinder that gets the fuel economy of a diesel. The engine puts out 238hp and 295lb-ft of torque and a mild hybrid system gets better than 39mpg in a vehicle the size of an S-Class. The use of direct injection, variable valve control, turbocharging, have allowed them to create a combination HCCI engine and standard gas engine that operates in compression ignition mode under light loads and spark ignition at other times. This allows it to operate with only a standard three-way-catalyst rather than the expensive diesel after-treatment systems. Now they just need to get it into series production.

[Source: Mercedes-Benz]
Stuttgart – The performance of a gasoline engine, the high torque and fuel economy of a state-of-the-art diesel together with extremely clean emissions: Mercedes-Benz has combined all the advantages of both engine types in its DiesOtto powertrain. The new technology package, which stands for the future of the gasoline engine, includes features such as direct gasoline injection, turbocharging and a variable compression. At the core of this innovation lies the controlled auto ignition, a highly efficient combustion process similar to that of a diesel. By way of another advantage, and in contrast to comparable developments, the Mercedes system requires no synthetic fuels but can be operated using conventional gasoline.
Optimising the internal combustion engine is one of the milestones on the Mercedes-Benz roadmap for sustainable mobility. BLUETEC has already made it possible for Mercedes engineers to make the powerful and economical diesel as clean as the gasoline engine. In the US this technology has already been available in the E-Class since 2006, and it will also become available in Europe from the end of this year. The E 300 BLUETEC will be by far the cleanest diesel in its class, and will meet the requirements of the EU5 exhaust emission standards in full.
"Our next goal will now be to make the gasoline engine as economical as a diesel. All the preconditions for this are provided by our DiesOtto concept, which incorporates the foremost strengths of both the gasoline engine and diesel engine," says Prof. Dr. Herbert Kohler, Head of Group Research & Advanced Engineering Vehicle and Powertrain; Chief Environmental Officer of DaimlerChrysler.
The result of this " marriage " is a four-cylinder unit with a displacement of just 1.8 litres, which combines the strengths of the low-emission gasoline engine with the fuel economy of a diesel. Despite its considerably reduced displacement – downsizing is one of the major factors for achieving a lower fuel consumption – this compact power unit delivers superior performance together with refinement at the level of the luxury class. An output of 175 kW/238 hp and a maximum torque of 400 newton metres are achieved together with the hybridisation a fuel consumption of less than six litres of gasoline per 100 kilometres. This figure by no means relates to a small or compact car, but to a vehicle the size of the current S-Class, with the level of comfort and safety that is typical of a Mercedes.
Mercedes-Benz DiesOtto – a further development of the spark-ignition engine
" In line with the worldwide success of today's diesel engine, vehicles equipped with gasoline engines will continue to have a long-term attraction for many customers and in many markets. Accordingly we are giving our attention to both engine types – including a full hybrid option for diesel and gasoline vehicles, " says Prof. Kohler. Mercedes-Benz is working on its DiesOtto concept with corresponding emphasis. Its key technological features are as follows:

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Downsizing with fewer cylinders and a smaller displacement
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Turbocharging for superior performance
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Direct gasoline injection as a further fuel economy measure
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Controlled auto ignition, a combustion process similar to that of a diesel
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Variable valve control
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A variable compression ratio leading to even better fuel economy and, depending on customer needs and the type of operation,
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A hybrid module with an integrated starter/generator, which makes the drive unit even more economical.

When starting and under full load, the fuel/air mixture is ignited by a spark plug, as in a conventional spark-ignition engine (homogeneous combustion). The controlled auto ignition to which the DiesOtto automatically reverts within its working cycle occurs under partial load conditions, i.e. at low and medium engine speeds.
The result is the very low nitrogen oxide emissions of homogeneous combustion at reduced reaction temperatures. All further emissions control in the DiesOtto engine is by means of a standard three-way catalytic converter. A highly efficient engine management and control system has also been realised to combine the individual sub-systems into a drive concept.
The current prospects for the future of the internal combustion engine reveal its great potential, and show that the new drive concept is a feasible proposition in the mid-term. Some of the intermediate solutions incorporated, e.g. direct gasoline injection, are already in series production at Mercedes-Benz. Others will be gradually integrated into series-production engines until the overall solution has been realised.