Direct Injection Gas Engines

Your assumption is wrong. Direct injection gas engines still have air flow throttled, so will have a butterfly valve or equivalent on the air intake, and some kind of air flow sensor. This is not something new, M-B was running D-I gasoline racing engines in at least as early as the 1950s, and they were throttled too.

Direct injection of a spark ignition engine does not turn it into a Diesel-cycle compression ignition engine. As diesels go to direct injection, losing the benefit of injection into the narrowly defined combustion environment of a pre-combustion chamber, we may find they need air flow management as well.

I believe any current production gas engine will need to maintain a fairly consistent air/fuel mixture to avoid running lean which will lead to emissions issues. They will all either have a throttle plate or have more significant control over the intake valves which can act as a throttle by keeping them mostly closed. BMW probably leads in this technology although I'm not sure how widespread it is in production.

There is talk of making gas engines that will operate more like a diesel under certain load conditions. They are being tested. Homogeneous-charge-compression-ignition (HCCI)is what GM calls it. It would probably still have a throttle since it is spark ignition much of the time.

Me Again wrote:

You quoted something that I did not write! Chris

Sorry about that - fixed it.

itguy08 wrote:

Me Again wrote:

The Ecoboost engines have a mass air flow sensor, and control the amount of air going into the engine with something similar to a throttle plate. Only change is the fuel is not injected into the air intake manifold, but into the cylinders directly, in a more energy efficient manner.

Ecoboost is a speed sensity style system with no MAF. There is most definitely a throttle plate on the engine.

There is a really good tech article on the EB 3.5 here:
Ecoboost 3.5 Info.

The lack of engine braking is more to do with the turbochaurgers than anything else. Not sure how but turbocharged cars (and trucks) have less exhaust braking than regular cars. I definitely notice the lack of engine braking in the Ecoboost. But Ford has some sort of Agressive fuel shutoff during decelleration that helps somewhat.

You quoted something that I did not write! Chris

Golden_HVAC wrote:

The Ecoboost engines have a mass air flow sensor, and control the amount of air going into the engine with something similar to a throttle plate. Only change is the fuel is not injected into the air intake manifold, but into the cylinders directly, in a more energy efficient manner.

Ecoboost is a speed sensity style system with no MAF. There is most definitely a throttle plate on the engine.

There is a really good tech article on the EB 3.5 here:
Ecoboost 3.5 Info.

The lack of engine braking is more to do with the turbochargers than anything else. Not sure how but turbocharged cars (and trucks) have less exhaust braking than regular cars. I definitely notice the lack of engine braking in the Ecoboost. But Ford has some sort of Agressive fuel shutoff during decelleration that helps somewhat.

rjstractor wrote:
I'm not an automotive engineer, but I do know that my dad's F250 with the 7.3 diesel and 6 speed manual provides far less engine braking than a buddy's F250 with a gas V10 and 5 speed manual, having driven both.

I am not either, but I know my Dodge diesel/auto would slow down on the downhill side of a hill that the Chevy Express van 350/Vortec/auto I drove at work would not with just taking foot off of throttle. In fact the Chevy speed up. Go figure.

Yep. My 2001 Dodge/Cummins did not lock the torque converter on compression in OEM trim and more or less just free wheeled down hills. Enter grade braking (which kept the TC locked). Dodge did not do that until to 2005 I believe. However the V8's seem to hold back better than the I6's.

In 2005(?) Dodge finally authorized exhaust brakes on auto tranny trucks.

Chris

BenK wrote:

Never looked closely into exhaust braking and admit to not really knowing how
they work.

From listening to them on the road, guessing that they block and release the
exhaust so that the pumping losses are increased. Therefore engine braking, but
that is just a guess till find time to read up on them (not motivated just yet
but if the direct injection systems do not have throttle's, then this might also
work on gasoline ICE's)

A exhaust brake is just a butterfly valve in the exhaust pipe. Or on the new light duty diesels with a VVT you close the turbo vanes. Either way you close the exhaust to increase backpressure, and pumping losses. The large diesels use a timed compression release. The exhaust valve is opened at TDC on the compression stroke, dumping the compressed air into the exhaust and not pushing the piston back down. The air dumping into the exhaust is what makes the noise you hear

Golden_HVAC wrote:


Somehow I don't think you have ever taken apart a car, and figured out what is inside.

When I owned a 1984 Diesel Isuzu, it had a manual transmission, and was great at slowing down by downshifting. The fully open air intake fills the cylinders with air, and then without your foot on the throttle, only a tiny amount of idle fuel level is injected, so barely any fuel is added to the cylinders, and you get a lot of braking action.

At the same time, the Ford diesel trucks used a transmission that did not like to transfer the maximum amount of engine braking as the engine could develop, so Ford decided to put the transmission into neutral while slowing, giving very little engine braking with the automatic transmission. If you selected the manual 5 speed (back in the 80's) then you get wonderful compression braking, yet not nearly as much as if you have a engine brake too.

Fred.

On the Older Ford and the Jeep Liberty diesel I don't think the tranny goes into neutral but rather the torque convertor goes into free wheeling to remove the engine braking. I haven't seen the actual engineering data so I could be wrong. The same end result tho. :)

In the carbed engines of the past which way did the engine turn faster with the starter, throttle plate open or closed? How about your riding lawn mower, throttle plate open or closed (no choke)?

Another question for everyone. Approx how much more power is required to turn a gas engine rpm for rpm compared to diesel engine or vice versa? (It varies somewhat depending on the engine model's valving, compression ratio, etc.) Give an approx.

When Cummins went from the two valves per cylinder to 4 valves in the I6 5.9 liter engine Used in the Dodge pickup they also increased the compression to ? and ? according to their engineering data?

I cant tell you how my 08 psd works but it will hold back my 8500lb TT and my 12-1500lb golf cart in the bed on any hill I have come across with out having to hit my brakes. I have been all through tenn,wv, nc etc