h a l f b a k e r yWhy not imagine it in a way that works?
add, search, annotate, link, view, overview, recent, by name, random
news, help, about, links, report a problem
browse anonymously,
or get an account
and write.
register,
|
|
|
One of the main problems with turbochargers is that they do not provide an immediate power boost when you step on the gas pedal, My idea is to attach an "exhaust brake" type mechanism probably to the outlet side of the turbo, of course it would probably have to have some kind of a waste gate so the engine
can remain running at idle. I suppose the engine would have to run slightly harder at idle than normal to maintain pressure. it could be computer controlled with a pressure sensor or simply push button operated.
Here is an example of usage with this system, Imagine you're traveling down a road at a relatively high speed and you're starting to approach a moderately sharp turn, you’ll of course have to slow down so you activate your exhaust brake and use engine braking which will also build up pressure as soon as you pass the apex of the turn you deactivate your exhaust brake which releases the pressure directly through the turbo and you'll instantly and quickly accelerate back up to speed.
Or another example could be that you're idling at a red light or at a starting line, you simply deactivate your exhaust brake and you have instant acceleration.
Turbocharger
http://auto.howstuffworks.com/turbo.htm
a standard turbocharger [BJS, Jul 29 2005]
Pacbrake Exhaust and Engine Brakes
http://pacbrake.com/how_they_work.php
"The most favorable location to mount an exhaust brake is to the outlet side of the turbo charger. " [baconbrain, Jul 29 2005]
Exhaust Brake
http://www.pplmotor...t-brakes-diesel.htm
pplmotorhomes [BJS, May 12 2006]
[link]
|
| |
//allowing a diesel engine to mimic a down-shifted gasoline engine// That's something I didn't know [baconbrain] - does downshifting not provide engine braking on a diesel? What happens? |
|
| |
A gasoline engine changes power by varying the amount of air going into the engine via a throttling valve (the fuel is sucked in as a side effect). A diesel engine changes speed by varying the amount of fuel that is injected into the air, which flows freely. |
|
| |
A down-shifted gasoline engine with the throttle closed is trying to pull more air than it can get, and acts like an air un-compressor, which takes work, which slows the car. A diesel engine with the fuel shut off keeps moving air through, and doesn't do any work to the air. So big trucks must depend entirely on their mechanical brakes while descending a mountain road with 30,000 pounds of bananas. |
|
| |
So, they install engine brakes that pop the exhaust valves open at top dead center, which turns the engine into an air compressor, and makes a hell of a racket past your motel at 3 AM. |
|
| |
Smaller trucks install exhaust brakes, which install a throttle valve in the exhaust flow, blocking it and making the engine into an air compressor. BJS hopes to use that compressed exhaust to drive a turbine, I think. I think diesels are doing that already. |
|
| |
Great explanation [baconbrain] - I'd never really thought about it, but it makes sense, thanks, though I'm puzzled why it only works in the small hours of the morning ;-) |
|
| |
I think that a reservoir would be needed, between the exhaust manifold and the turbo. |
|
| |
Yea, thats pretty much what I was thinking... |
|
| |
With a diesel, it would be straight air, since at zero throttle there would be zero fuel in the engine. But with a gasoline engine, it would be the exhaust gasses because combustion would still be taking place. You might be able to shut off the fuel while braking with this method, but it might be better to use BJS's method and use the compressed gasses to drive the turbine, so as to keep the engine running. |
|
| |
If what "rasberry re-tart" said is true, than wouldn't the engine stop running if you took your foot off the throttle? Whould you always have to have your foot on the peddle for the engine to remain running? |
|
| |
No, diesel engines only cut out the fuel supply when you are compression braking, in other words when the engine is taking up more power than it is putting out, like while going down a hill in low gear. The engine doesn't need combustion to keep it going, since the momentum of the truck is keeping the engine turning. At least, that was how I was told it worked. |
|
| |
In this situation, the engine and also the turbo are acting like brakes, turning the truck's forward motion into heat energy by compressing air. At this time, you could store some of this compressed air coming out of the exhaust and later inject it into the intake manifold for more power. |
|
| |
If you were storing up exhaust gasses from a gasoline engine, you could only use these to spool up the turbo, since they wouldn't have much oxygen left. You could also use a turbo or supercharger to compress air at idle or while braking for later use. |
|
| |
Actually, any fuel-injected gasoline engine also turns off its injectors when under compression-braking; they'll usually be turned back on as the revs drop below a setpoint in the ECU. |
|
| |
You can watch this happen with a wideband O2 sensor connected to a gasoline engine: the injectors will shut off pretty much the instant the ECU detect a fully-closed throttle plate, making the AFR of the combustion chamber mixture shoot up to ~20.9% (the amount of oxygen in free air), as the revs drop below a pre-described setpoint (about ~1900 RPM in my car), the ECU turns the injectors back on, and you'll see an AFR closer to 14-15. |
|
| |
And, if you're in a car w/o much sound deadening and/or stiff engine mounts, you can usually feel the little shudder as the injectors are turned back on. |
|
| |
[bripab007] But it IS cool to see the machine belching flames if its too rich on decel. I.E. Dipping into turn one at Texas World Speedway coming off the banked front straight. At any rate, I like the concept of the idea, however I remain unimpressed that you're "not even 16..." Your scoutmaster not giving you enough hugs or something? |
|
| |