Direct Injection Gas Engines

Golden_HVAC wrote:

Me Again wrote:
With the trend to direct injection gas engines what happens going down a hill on compression. Diesel engines without intake butterflies have little hold back on compression, so I assume that gassers without an intake butterfly will be the same. So if one has a pickup with a direct injection turbo charged gas engine some day are they goes to implement an exhaust brake into the turbo like the modern diesels?

Fords Ecoboost is direct injection! what happens with it under compression. Without a restriction in the intake or the exhaust most of the energy to compress a cylinder is returned on the down stroke.

Chris

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.

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.

With the turbocharge engine, you do get more air into the cylinders, and compression braking still works well. Ford has been able to shut off fuel injection into the engines for a number of years, to add compression braking while the engine is over a certain RPM, say over 2,000 RPM, no fuel would need to be injected to the air intake - adding to increased compression braking.

Also it matters how durable the transmission is. Since model year 2000, the Ford automatic transmissions have been able to handle substantial amounts of engine braking going through them. Well into the 200 horsepower of engine braking is possible today to get transferred from the rear wheels through the transmission into the engine for slowing.

My sister's F-150 Ecoboost has lots of engine braking effect. It also has 6 speeds to downshift into, and can change the engine RPM into several higher speeds, to increase engine braking according to the engine RPM.

Fred.

Fred, I will let someone else correct your thoughts as you do not seem to think I know anything.

Read this in the mean time.
http://en.wikipedia.org/wiki/Gasoline_direct_injection

I have two switches to control my smart controller for torque converter lockup and exhaust brake.

I can tell you that at 20,500-21,000 gross going down a hill with the torque converter locked with the exhaust brake off, there is very little hold back compared to have the exhaust brake on.

Hold back based on engine internal resistance is in not much compared to an exhaust brake. That is why both GM and Ford moved from grade braking to exhause braking on the newer trucks.

So unless Ford is playing with intake valve cycling, then the Ecoboost will be similar to a diesel without an exhaust brake.

Chris