| Mercedes has developed a variable
compression gasoline engine that uses a controlled automatic ignition,
a process similar to that of diesel. Unlike Volkswagen’s approach
to such an engine, it runs on ordinary gasoline, not synthetic fuel.
The system achieves an output of 175 kW (238hp) and peak torque of 400Nm.
In the S-Class luxury sedan it achieves fuel economy of 6 litres/100km.
The prototype engine is a downsized 1.8-litre four-cylinder unit that
combines direct gasoline injection, twin sequential turbocharging and
a variable compression. It is then joined to a hybrid drivetrain with
an integrated starter-alternator.
Advanced engineering chief Dr Herbert Kohler said: “The concept
is a feasible proposition in the mid-term. Gasoline direct injection is
already in series production. We’ll gradually integrate the other
technologies into series-production engines until the overall solution
has been realised.”
Mercedes said some of the technologies would be introduced in the next
two years. The company will have to address noise issues before the full
system with variable compression can be introduced. As the engine switches
between the two modes, the change in NVH characteristics is apparent to
drivers.
When starting and under full load, a spark plug ignites the fuel-air mixture
is ignited by a spark plug, as normal. Under partial loads, the compression
ratio increases and the engine self-ignites the fuel mix. The resulting
homogeneous combustion at lower temperatures reduces NOx emissions.
A standard three-way catalytic converter handles aftertreatment.
© Automotive Engineer, 2007 |
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