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Diesel Engine Production Efficiency
Name: Peter
Status: Other
Grade: Other
Location: Outside U.S.
Country: England
Date: January 2008
Question:
I can understand that to operate
efficiently, a diesel engine requires a higher
compression ratio than a petrol engine and as a
result the diesel engine needs to be made from
stronger materials to reduce breakdowns. But, can a
diesel engine be mass produced more cheaply than a
petrol engine!
Replies:
Hi Peter,
No, a diesel engine can never be made more cheaply than a gasoline
(petrol) engine. The addition strength needed is only a minor
contributor to cost. The main thing that makes a diesel motor more
expensive is the requirement for a high pressure (greater than 20,000
psi on modern engines!) direct cylinder fuel injection system. This is
far more expensive than even the most sophisticated gasoline injection
systems. A diesel injection system requires this super high pressure,
ultra-precision fuel pump, whereas a gasoline engine's injection
system's pump is a relatively simple electric pump that needs to
develop only 30 to 90 psi. It is mainly the fuel system that makes the
diesel engine so much more costly, and this is driven by the
requirement that the fuel in a diesel engine must be injected directly
into the combustion chamber, whereas a gasoline engine can operate
very well with fuel simply being injected into the inlet manifold,
right behind the inlet valves. So called "direct injection" (into the
combustion chamber) requires far higher pressures than so-called
"port" (manifold) injection, and high pressure pumps are highly
expensive, and high precision components.
Regards,
Bob Wilson
A diesel engine uses a higher compression ratio not only for thermodynamic
efficiency, but also so to achieve compression ignition, that is, the air in
the cylinder gets hot enough when compressed to ignite the injected diesel
fuel.
It does not seem possible to manufacture a diesel engine for lower cost than
gasoline engine because the diesel must be more rugged and also requires a
much more costly high-pressure fuel injection system (tens of thousands of
psi). A spark-ignited gasoline engine uses a comparatively simple low-pressure
fuel injection system and milder compression ratio.
Robert Erck
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Update: June 2012
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