Engine braking Gas Vs Diesel

Thanks for the replies, I was just wondering.
Yes my big truck had a jake brake but unloaded truck and trailer( 30k lbs) it wasn't needed.

ktmrfs wrote:

brulaz wrote:


Apparently some eliminate the air throttle plate according to Wikipedi anyway:

Wikipedia on GDI wrote:
In addition some engines operate on full air intake. That is, there is no air throttle plate eliminating air throttling losses in some GDI engines, when compared to a conventional fuel-injected or carbureted engine, which greatly improves efficiency, and reduces piston 'pumping losses'. Engine speed is controlled by the engine control unit/engine management system (EMS), which regulates fuel injection function and ignition timing, instead of having a throttle plate that restricts the incoming air supply.

I'm seeing aftermarket replacements for the 3.5L Ecoboost throttle body, complete with butterfly valve, so I guess that engine does have an air throttle plate. http://www.stage3motorsports.com/1822-1-2011-2013-F150-37L-BBK-73MM-Throttle-Body.html, so that should help with engine braking.

I'm suspicious of the wiki article claim. Gas engines need to operate over a vary narrow air/fuel ratio. So there must be some way to control the air volume entering the cylinder. Throttle plate or something. It may be located downstream of where one might expect it, but still there must be a way to control air volume in the form of some kind of variable restriction on the airflow.

Diesels will operate over an extremely wide air fuel ratio, so the throttle plate is not needed to control the amount of incoming air.

Hence less pumping losses but also less restriction under no throttle operation and hence less braking.

There is only 1 engine maker I'm aware of running without a need (but it still has one) for a throttle plate. That's BMW's valvetronic motors. They only use the throttle plate for start-up and warm-up (as in a choke), but once warm, all throttling is handled by valve lift.

I believe Audi/vwag still uses a throttle plate. I owned a 2007 Saturn Sky Redline that had direct injection, but it also had the customary throttle body as well.

lenr wrote:
...I don't believe that Ford ever had an exhaust valve style brake; just vane control starting in 2011. I find that my 2012 works just fine in tow haul mode with cruse within 10 mph of the cruse setting. So just set it 10 mph less than what you want to max at as you crest the mountain. You do need to be able to watch the rpms run up toward 4000, but that is where red line is.

The 6.0 PSD used a VGT that was vacuum driven and did provide exhaust braking. It was not as effective as my new 6.7 CTD, but it worked well on my F250.

It is confusing because Ford used the play on words "Single Sequential Turbo" which makes it sound like 2 turbos. No harm.

lenr wrote:
2008 - 2010 were the only years that Ford used a compound turbo. 2011 - 2014 used a single turbo with a double compressor wheel. The desired effect was quicker spool which it does. Two downsides are reduced engine braking through turbo vane control and running out of air at higher altitudes. So, in 2015 Ford went to a larger single wheel turbo to get more torque, more HP, more go at high altitudes, and more slow coming down the mountain. Repotedly it does spool slightly longer. I don't believe that Ford ever had an exhaust valve style brake; just vane control starting in 2011. I find that my 2012 works just fine in tow haul mode with cruse within 10 mph of the cruse setting. So just set it 10 mph less than what you want to max at as you crest the mountain. You do need to be able to watch the rpms run up toward 4000, but that is where red line is.

You are correct, the 2011 to 2014 did use am SST
Sorry, I am more up to date on Cummins engines than the new Ford diesels.

2008 - 2010 were the only years that Ford used a compound turbo. 2011 - 2014 used a single turbo with a double compressor wheel. The desired effect was quicker spool which it does. Two downsides are reduced engine braking through turbo vane control and running out of air at higher altitudes. So, in 2015 Ford went to a larger single wheel turbo to get more torque, more HP, more go at high altitudes, and more slow coming down the mountain. Repotedly it does spool slightly longer. I don't believe that Ford ever had an exhaust valve style brake; just vane control starting in 2011. I find that my 2012 works just fine in tow haul mode with cruse within 10 mph of the cruse setting. So just set it 10 mph less than what you want to max at as you crest the mountain. You do need to be able to watch the rpms run up toward 4000, but that is where red line is.

Bedlam wrote:
I wonder if variable valve timing could accomplish the same control as the throttle plate.

Variable Valve Timing only controls when the valves open, and not how much it opens which is what is needed to control the air/fuel ratio. VVT basically rotates the cam to control the moment when the cam lobes push the valve down. The amount the lobe pushes the valve down is not controlled. You can in theory have a slant lobed cam that moves front to back to control how far the valve opens, but that would be adding more cost and more complexit to something as low cost and simple as a throttle valve. Or you can have some sort of motor controlling tha valves, but again it will add cost and complexity with not much of an added benefit over a throttle valve.

Bedlam wrote:
I wonder if variable valve timing could accomplish the same control as the throttle plate.

By varying intake valve duration, lift and timing It could, but the effect would be the same, a restriction at low loads. In either case it would end up "sucking through a straw" under low loads.

And many vehicles do vary intake valve duration timing or lift to to give a broad torque curve and high horsepower. In fact, I'd say the majority of gas engines are doing this.



In fact, even back as far as 1991 this was done on some cars. I have two 199y7 mercedes that vary the intake valve timing over about 30 degrees to give good torque and good idle at low rpm and good breathing at high rpm for high peak power. The result is a very broad flat torque curve. This was done starting in 1990 on the engines I have. Back then it was pretty amazing in that they were getting above 1HP/cubic inch on a normally aspirated gas engine. Course today that is ho/hum, but then it was state of the art.

The other thing that can be done is using the atkins or miller cycle for improve efficiency. That entails adjusting the valve timing and duration such that most of the intake air goes through the exhaust at low rpm giving very little air in the combustion chamber during the compression stroke. The downside is very poor low end torque. so it has been either combined with turbocharging or used with hybrid vehicles. Of course to do this, it requires direct injection so the intake air isn't also full of fuel.

Thinking about it, this may be the engines wiki was referring to that don't have a throttle plate.

And I would expect these gas engines wouldn't have much engine braking either.

I wonder if variable valve timing could accomplish the same control as the throttle plate.

brulaz wrote:

kyle86 wrote:

Me Again wrote:
I wonder how the new direct injection gas engines are doing that have no butterfly valve? Audi, BMW and Mini Cooper all have engines in production with DI.

I was under the impression that DI just places the fuel injector in the combustion chamber instead of the intake runner. They should still have a throttle body to let air into the engine. I could be wrong.

Apparently some eliminate the air throttle plate according to Wikipedi anyway:

Wikipedia on GDI wrote:
In addition some engines operate on full air intake. That is, there is no air throttle plate eliminating air throttling losses in some GDI engines, when compared to a conventional fuel-injected or carbureted engine, which greatly improves efficiency, and reduces piston 'pumping losses'. Engine speed is controlled by the engine control unit/engine management system (EMS), which regulates fuel injection function and ignition timing, instead of having a throttle plate that restricts the incoming air supply.

I'm seeing aftermarket replacements for the 3.5L Ecoboost throttle body, complete with butterfly valve, so I guess that engine does have an air throttle plate. http://www.stage3motorsports.com/1822-1-2011-2013-F150-37L-BBK-73MM-Throttle-Body.html, so that should help with engine braking.

I'm suspicious of the wiki article claim. Gas engines need to operate over a vary narrow air/fuel ratio. So there must be some way to control the air volume entering the cylinder. Throttle plate or something. It may be located downstream of where one might expect it, but still there must be a way to control air volume in the form of some kind of variable restriction on the airflow.

Diesels will operate over an extremely wide air fuel ratio, so the throttle plate is not needed to control the amount of incoming air.

Hence less pumping losses but also less restriction under no throttle operation and hence less braking.