Comments by "Keit Hammleter" (@keithammleter3824) on "" video.
-
1
-
@KrasYnek : No, you are wrong. The reason why exhaust gasses pass from the cylinder to the exhaust when the valve opens is because the pressure in the cylinder is higher - it is the pressure difference that drives the transfer - noting else. if the pressure in the exhaust manifold rises, that transfer is restricted. If the transfer of mass is reduced, the pressure in the cylinder remains high and is still high when the intake valve opens, restricting intake. If the exhaust manifold pressure is high enough, no mass transfer occurs at all. Nothing can get out the cylinder, so nothing can get in. The piston is just compressing and releasing that same mass all the time, its just a spring and not much engine braking.
Contrary to what some posters apparently think, Jake brakes on trucks work by opening the exhaust valve just after the compression stroke - so there is normal compression of intake air, but no power stroke, which normally returns the compression energy to the crankshaft even if no fuel is injected and burnt..
This is the key to understanding things - in normal operation energy from the crank is transferred to the cylinder gas during the compression stroke, and transferred back to the crankshaft during the next power stroke - no energy is lost, and therefore no engine braking. Engine braking that does occur without a Jake brake occurs because of mechanical friction and because of the net transfer of gas mass from intake to exhaust. No transfer - not much braking.
1
-
@KrasYnek : You can't be that dumb. In an engine, pressure created by combustion AND expansion is used to produce mechanical energy at the flywheel. In an air compressor, mechanical energy is used to pressurise and compress the air.
If you plug the engine exhaust, sure the piston compresses the air twice per 4 stroke cycle, but its compressing and expanding the SAME air each time -nothing can get out, so nothing can get in. So. as I said, its just like replacing the cylinder with a spring - energy is taken FROM the crankshaft in each compression, but GIVEN BACK during expansion (ie the nominal power and intake strokes).
To get a braking effect you must have a through pumping of air - as in normal engine braking, using a Jake brake, or an air compressor forcing air into a tank. If tank pressure is allowed to rise so high that the compressor can't push more air through, the mechanical power to turn the compressor crank goes down.
Jake brakes are much more effective than a normal throttled back engine because, and only because, the engine compression of the air occurs, but as the exhaust valve opens at about top dead centre at the end of the compression stroke, the air passes to the exhaust system WITHOUT expanding during a power stroke. So energy passes from crank to air and NEVER RETURNED. it's venting the air to the exhaust system at full compression instead of after expansion that causes the distinctive sound.
If it isn't a pressure difference that causes engine exhaust gasses to pass into and through the exhaust system, what the heck do you think causes it???
1
-
1