Lean, Green Machine

Newcastle Herald

Wednesday February 20, 2008

writes Brent Davison

ABOUT three days after the first Gulf War turned ugly, someone figured the price of oil was going to go high and stay high.

Then, soon after the end of that war, a lot of people realised Middle East crude was about to experience supply issues.

And soon after the current Gulf War got messy, most of us were able to figure out that there might be a bit of truth to the rumour that oil was a dwindling finite resource.

The dual notions that we were not only poisoning ourselves to death on our own exhaust fumes but also contributing to global warming also served as cause for concern.

Which is why, for a long time now, the world's car companies and best engineering brains have been developing short-, medium- and long-term solutions to the problem.

In the past decade we have seen petrol-electric hybrid power systems, stop-start engines that switch themselves off when cars stop, cleaner diesels and forced-induction engines tuned for economy first and performance second.

And now Mercedes-Benz has shown another alternative which, it says, will gradually filter through as a production engine.

Called the Diesotto, it combines, as its name suggests, principles from both the diesel engine and the Otto Cycle (ordinary four-stroke) engine.

The engine effectively packages almost every current system into one unit and then adds a couple of things that have, until now, been largely experimental.

Starting with a 1.8-litre, four-cylinder unit (a small capacity seen as a prerequisite for fuel economy) Mercedes-Benz engineers added direct fuel-injection, turbocharging and a variable compression ratio. It also includes homogeneous charge compression ignition so that, after starting and running in normal fashion from cold, the engine will behave like a diesel for normal running, using internal heat and compression to ignite the air-fuel mixture.

In other words, a small-capacity engine combining the strengths of a low-emission spark-ignition engine with the fuel economy of a diesel.

The engine has already had service in a development prototype known as the F700, a car that is as big as a current S-Class sedan, complete with luxury and safety features.

Power output is an impressive 175 kilowatts and just to give it a bit of extra clout it is mated to a 15-kilowatt electric power unit. Torque output is an equally impressive 400 Newton metres.

There are other numbers that are just as important though.

Fuel consumption is a claimed 5.3 litres/100km, carbon-dioxide output is a meagre 127 grams/km and nitrogen oxide levels are "a very low level" because of the homogeneous combustion at lower reactive temperatures.

Despite all of that the exhaust system is a conventional closed loop catalytic converter.

How long before we see Diesotto-engined Mercedes-Benzes?

"Features such as direct fuel-injection are already used in current Mercedes-Benz models such as the E 350 CGI and CLS 350 CGI. Other Diesotto modules will gradually enter series production during the next development stages," a company spokesman said.

The Diesotto was recently awarded the Environment Grand Prize for technological achievement in the fields of environmental protection and safety at the 23rd Festival Automobile International.

iQ BABY SET TO ROLL PAGE 54

Brent Davison has fun with the energetic VW Polo GTI in Saturday Drive

© 2008 Newcastle Herald

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