Kinda off topic, and might be a stupid question. But, A diesel engine that has a throttle plate in the intake, like the new dmax I noticed had one.. Does that create a vacuum at all, or is it just there for emmisions so they can regulate how much air is going in?

 

The "throttle plate" on the 6.blow and the Duramax are to help the engine draw in more EGR (exhaust gas recirculation) gasses to dilute the air/fuel mixture and lower NOx (oxides of nitrogen) emissions.

Cody

 

Because the combustion isn't perfect.

Gas engines often have three way cats. They convert carbon monoxide (CO,) hydrocarbons (HC,) and oxides of nitrogen (NOx.) If a gas engine runs rich, even VERY slightly, it will produce CO and HC. If it runs lean, it will produce HC and NOx. If it runs PERFECTLY at stoich, and EVERY molecule of oxygen is used to combust EVERY molecule of gas, it might be able to pass emissions without a cat. But it is impossible to run the engine EXACTLY at stoich, and have sufficient mixing to make all the molecules meet and combust.

The O2 sensors work by moving the air/fuel slightly above and slightly below stoich. Since it isn't perfect every time, it is the job of the catalyst to clean up the emissions.

 

It's there for reducing the shut down shudder. And also, I suspect, if you have a runaway engine you can stop it by turning off the key.
At least on the VW TDI when you turn off the key the throttle plate closes until the engine stops, then it opens back up again.

 

What Kwikkordead says is true. In some oilfield areas you are required to have one on your diesel truck to get on the jobsite. The reason is if you have a gaswell blowout and natural gas escapes into the atmosphere the engine will run away due to the fuel in the air and the only way to stop it is with a shut down plate.

 

well the throttle plate only lasted tile early 04's. it was taken out of operating strategy in early 03. it was like a backup plan for the feds but ford did not need it later on.

 

So in other words, they run a little rich most of the time?

 

thanks guys!

I've had all my questions answered, and even am learning some other stuff from other people posting that I didn't even know enough to ask about yet (ie the throttle plate to prevent 'dieseling' after the key is off) .

But I do have one gripe for both gas and diesel engines. Please correct me if im wrong (i don't know if this is a legit gripe or not), but IMHO, I think that EGR is a pretty cheapey way for automakers to meet emissions standards. If they really tried, they could probably design an engine that wouldn't have to suck in its exhaust to get the emissions right. It just seems kind of like the easy way out to me. What happens if you cut off the EGR (besides the obvious increase in bad emissions)?

Ok wait, I just thought of one more question...
In my home state of Texas, my X is exempt from yearly emissions tests during safety inspection because it weighs so much, but my question is do they have a different 'sniffer machine' for diesel trucks? I think regular superduties don't weigh enough to be exempt, but I can't imagine that a diesel truck would pass a sniffer test designed for gassers. So, do they have a differnt machine, or are all diesels exempt, or do they just run on the same machine with the criteria changed?

Thanks again guys!

Isaac

 

Half of the time. The other half they are on the lean side of stoic. The engine management constantly sweeps it back and forth from lean to rich. It's done that way to charge the exhaust stream with a little extra oxygen so that there is enough left over oxygen for the catalyst to do it's work.
Minimum crosscount from lean to rich and back again is 11 times in 5 seconds. Most cars will do around 40 times every 5 seconds.
On my old Matco scanner you can see it graphed like a sine wave.