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Mercedes-Benz Presents the Combined SI-CAI “DiesOtto” Concept Engine
25 July 2007
Mercedes-Benz provided some details on its DiesOtto engine project: a 1.8-liter, turbocharged, four-cylinder gasoline direct injection engine that supports a switch to controlled auto ignition (CAI) under certain operating conditions.
When starting and under full load, the fuel/air charge is ignited by a spark plug, as in a conventional spark-ignition (SI) engine. The switch to controlled auto ignition mode occurs under partial load conditions, i.e. at low and medium engine speeds.
Despite its reduced displacement—downsizing being one of the major factors for reducing fuel consumption —the research engine delivers an output of 175 kW/238 hp and a maximum torque of 400 Nm (295 lb-ft), with projected fuel consumption of less than 6.0 l/100km (39 mpg US). This, Mercedes-Benz said, could power a vehicle the size of its current S-Class.
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.
—Prof. Dr. Herbert Kohler, Head of Group Research & Advanced Engineering Vehicle and Powertrain; Chief Environmental Officer of DaimlerChrysler
Volkswagen has also earlier seized on the term “DiesOtto” to reflect its Combined Combustion System (CCS) work (earlier post). A number of automakers, engineering firms and universities are exploring ways to combine CAI/HCCI with conventional combustion systems as a way to increase the fuel economy of gasoline-fueled engines. (Earlier post.)
Some of the issues involved in engineering such combined systems include the design of control systems for cycle-to-cycle control, ways to enlarge the operating range for the CAI mode, and transient response.
Features of the Mercedes-Benz DiesOtto engine include:
Downsizing with fewer cylinders and a smaller displacement;
Turbocharging for enhanced performance;
Direct gasoline injection;
Controlled auto ignition;
Variable valve control;
A variable compression ratio; and
An optional microhybrid module with an integrated starter/generator.
The low temperature combustion reduces engine-out NOx. All further emissions control in the DiesOtto engine is by means of a standard three-way catalytic converter.
Mercedes-Benz noted that some of the technologies in the concept engine—such as gasoline direct injection—are already in production, while others will emerge in the mid-term. The company again emphasized that it is working on hybrid options for its models.
(A hat-tip to Rafael!)
Resources:
July 25, 2007 in Engines, Fuel Efficiency | Permalink | Comments (30) | TrackBack (0)
Comments
Posted by: Roger Pham | August 01, 2007 at 08:14 AM
Oh, maz, your question brings up another good point.
The variable CR along with the Atkinson cycle can also help reducing turbine inlet temperature. For example, when running on boost, the effective CR will be reduced to, say, 8 or 9, using variable intake valve timing, along with optional two-stage direct fuel injection, in order to prevent detonation, but the expansion ratio will still be 11 or higher, depending on the engine's geometric CR. Cooled EGR is another trick to help reduce NOx and exhaust tempature as well.
These tricks will definitely lower the exhaust temp enough such that one do not have to resort to enriching the fuel mixture, nor having to reduce the geometric CR, hence reducing efficiency, when running on turbo-boost.
Posted by: Roger Pham | August 01, 2007 at 04:20 PM
I want to know SI and CI engine difference(Table)
Posted by: Saikat Chowdhury | August 16, 2007 at 05:26 AM
No, Roger
In a basis of fuel economy the thermal efficiency lays. It does not depend on mode of valves work, and depends only on a compression ratio and coofficiant of adiabatic curve. Muller and Atkinson Cycles are created for increase of indicator efficiency.
If you can adjust a geometrical of compression ratio, first, you can increase a compression ratio on idling and increase fuel economy, and, second, you can reduce a of compression ratio on a mode of full loading and increase pressure of charge, thus to increase specific capacity. Then you instead of the American engine can apply the European engine with the same capacity, but with the best fuel economy.
Posted by: maz | August 23, 2007 at 01:47 AM
THERE WAS A 2.3LITER DIESEL TURBOCHARDED MUSTANG BUILT BY A MAN NAMED MOODY AND ANOTHER INVENTOR WHOSE NAME I DON'T KNOW.HOWEVER IT WAS REPORTED TO GET 87MPG COUPLE THAT TECHNOLOGY WITH HYBRID TECH OF TODAY.ALONG WITH LEAPS IN COMPUTER CONTROL AND VARIABLE VALVE TIMING.I'M SEEING 100-135MPG.IF RUMORS ARE CORRECT THE US CONGRESS WOULD'T LET THE CAR BE PRODUCED.GREED IS THE PROBLEM BEHIND OIL.
Posted by: timothy d cephas | November 27, 2007 at 08:34 PM
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No, but I would guess that the easiest way to achieve variable compression ratio (CR) would be variable intake valve timing. To lower effective CR, delay intake valve closure to after BTD, and to maximize CR, close intake valve right at BTD. Of course, inertia of the moving air mass must be taken into account and adjust the valve timing according to engine speed.