[Spridgets] Question - Jake Brake

[an5.sprite at gmail.com]

Thanks, great explanation.
Sent from my Verizon Wireless BlackBerry

-----Original Message-----
From: <bjshov8 at tx.rr.com>
Sender: spridgets-bounces at autox.team.net
Date: Sat, 26 Mar 2011 10:43:50 
To: <spridgets at autox.team.net>
Subject: Re: [Spridgets] Question - Jake Brake

That's correct.
In a diesel the engine sucks in as much air as it wants, the piston compresses the air, then at the top of the stroke assuming you aren't injecting fuel the compressed air pushes the piston back down.  It is like a spring- compress the spring then let the spring push back out and you haven't exerted any net work.  BUT if you do the work to compress the spring, then have a mechanism that releases the spring, you don't get the work back out of the spring.  In the diesel engine it compresses the air, then the jake brake opens and lets the compression out before the compressed air can push the piston back down.  So basically the engine is functioning as an air compressor.

> Jake Brakes work because the mechanicals are a bit different between
> diesel and gasoline engines.  A gasoline engine has a butterfly valve
> that limits air intake when the throttle isn't depressed, so there
> isn't much pressure built up on the compression stroke.  Diesel
> engines don't have these, and continue to build up pressure even when
> no throttle is active, and causes a bit of acceleration due to the
> pressure build up which forces the piston back down.   So Jake Brakes
> are extra mechanicals that release the pressure from the compression
> strokes, and that extra pressure getting released causes the "machine
> gun" sounds when the Jake Brake is activated and helps to slow the
> forward momentum of the vehicle.
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