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How is load control achieved in a diesel engine?

 
 
abq129
 
Reply Fri 26 Feb, 2010 05:42 pm
i've been thinking since some time....if a diesel engine( Compression Ignition) does not have a throttle valve then the amount of air which enters the cylinder must be essentially unchanged.....if that is so.......doesn't it create a lean mixture? in which there's too much air and less fuel.....if YES.....it should not ignite then :S
help me out!!!!

secondly,
if we use a throttle valve in spark ignition (petrol engine)...why do we need the poppet valves?although EFI systems are used...but considering the older designs...what was the logic behind using a throttle/butterfly valve when you could restrict the flow using poppet valves?
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Type: Question • Score: 3 • Views: 9,864 • Replies: 8
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JTT
 
  -2  
Reply Fri 26 Feb, 2010 06:43 pm
@abq129,
Rooccccckkkkkkyyy.
roger
 
  1  
Reply Fri 26 Feb, 2010 07:20 pm
@abq129,
Without poppet valves, you are not going to develope much compression, are you? Imagine the intake stroke filling the cylinders with fuel and air mixture as well as exhaust gas. Without valves, this is going to happen. Likewise, on compression stroke, the contents of the cylinders are going to be forced indiscriminately into both exhaust and intake manifolds. That is all that can happen without valves of some sort.

I believe diesels do have a throttle valve, but I don't know the systems that well. Like other systems involving injectors, you still need a throttle to regulate incoming air.
Rockhead
 
  1  
Reply Fri 26 Feb, 2010 09:34 pm
@JTT,
here, this guy talks better'n me...

how diesels work (15 minutes, grab a soda)
http://www.youtube.com/watch?v=K9ZkDXadpJk
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abq129
 
  1  
Reply Sat 27 Feb, 2010 06:38 am
@roger,
i totally understand the purpose of the poppet valves....the thing confusing me is the throttle valve/butterfly valve....why was this used in early engines? when u can restrict the flow using the poppet valves, why at all use the butterfly valve?

btw thanks man!!!
roger
 
  1  
Reply Sat 27 Feb, 2010 02:49 pm
@abq129,
I don't think I'm going to explain this really well, but poppet valves have a completely different function than the throttle valve. The poppets (usually just called "valves" are driven by the camshaft, which is geared to the crankshaft at a 1:2 ratio. The faster the engine goes, the faster the valves open and close. They are controlled by the engine speed. The engine speed is controlled by the throttle.

The throttle opening is controlled by the operator of the vehicle through linkage to the accelerator pedal. All else being equal, the more you open the throttle, the faster the engine runs. You could say that the valves determine the maximum amount of fuel and air that pass through the engine, but ignoring certain alleged Toyota problems, you don't always want it to run at maximum speed. The throttle valve allows you to decide how much of the engine potential you want to use.
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mrpookykin
 
  1  
Reply Wed 7 Dec, 2011 04:45 am
@abq129,
Most modern diesel engines do not have a throttle valve, only the amount of fuel being injected is varied. So under low load conditions the mixture is extremely lean. However, this does not matter as the fuel is ignited by the temperature of the air being compressed, so any fuel being injected will ignite, no matter how minute.
Many new BMW petrol engines also have no butterfly valve. Instead they use a system called 'valvetronic' which uses almost infinitely variable valve lift to "throttle" the engine.
0 Replies
 
hayder
 
  1  
Reply Thu 27 Mar, 2014 11:30 pm
good day every one
what's different between these terms in diesel engine
1-high load
2- low load.
3- full load
4- part load
if someone answers me, send his answer to my email "[email protected]"
thank you for all
0 Replies
 
abcxy
 
  1  
Reply Thu 25 Feb, 2016 05:02 pm
@abq129,
in diesel engine load is controlled by amount of fuel injecting
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