What car idles at 6,000 rpm?
-Curt
From: Scott Ritchey via Mercedes <[email protected]>
To: Mercedes Discussion List <[email protected]>
Cc: Scott Ritchey <[email protected]>
Sent: Monday, February 6, 2017 12:32 AM
Subject: [MBZ] Diesel Efficiency at Idle
Food for thought:
One reason Diesels are more efficient than gas engines is Diesels (mostly)
don't have throttles. This is mainly a factor low speed and at idle: gas
engine waste a LOT of power idling.
Consider a 3 liter (183 CID) engine that idles at 6000 RPM. The intake
manifold pressure would be near ambient for a Diesel but a gasoline engine
would idle at a manifold vacuum of about 20 inches (10 PSI). So the energy
required to turn the crank one full cycle (2 revs) would be 1830 inch-lbs or
152 ft-lbs. For 3000 full cycles per minute (6000 RPM), this is 457500
ft-lb of work per minute or 14 HP. So the hypothetical 3 liter gas engine
must produce 14 HP while stopped at a traffic light just to keep the engine
turning against manifold vacuum.
Scott
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