Oddball idea
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Steam engines did this many years ago with double and triple expansion steam engines. A turbocharger also scavenges some of the gas pressure but there are tradeoffs. Converting some of the waste heat would be good but adds complexity, expense, and weight also.
Thread Starter
|
Fleet Owner
Joined: Aug 2001
Posts: 29,941
Likes: 46
From: Drummonds, TN USA
I wondered about turbocompounding - I've heard the term before, but didn't stop to find out what the story was on it. I'd have probably not believed it, or thought that it was a means of increasing boost only...
Postmaster
Joined: Feb 2003
Posts: 4,043
Likes: 4
So, anyone know how much the air fuel charge expands after combustion? Is the exaust gas expanding when the valve opens or is it just being pushed out by the piston?
Here's what I'm getting at. The easiest way to make full use of the expansion of the combustion gas is to have the stroke long enough that the cylinder pressure is 0 psi at BDC piston travel. If the gas expands 200 times then the volume of the combustion chambe at BDC should be 200 times that at TDC. That would be a minimum since at that point the piston shoud be at around max velocity. So if the stroke was longer, some use could be made of the momentum stored by the piston. There is a limit to this because as soon as the gas stopps pushing on the piston, the load on the engine will start slowing it down.
Now if the gas actually isn't expanding when the exhaust valve opens and is indeed being pushed by the piston as it moves up, then that piston is being pushed by the next piston on a power cycle at that time. So if you attach a parasitic scavenging device on the exhaust stream, you will actually be using power from the next piston on the power stroke. That power could be used to drive the load on the engine.
I don't know if there would be a net power increase with your idea. Just offering some radom thoughts.
Here's what I'm getting at. The easiest way to make full use of the expansion of the combustion gas is to have the stroke long enough that the cylinder pressure is 0 psi at BDC piston travel. If the gas expands 200 times then the volume of the combustion chambe at BDC should be 200 times that at TDC. That would be a minimum since at that point the piston shoud be at around max velocity. So if the stroke was longer, some use could be made of the momentum stored by the piston. There is a limit to this because as soon as the gas stopps pushing on the piston, the load on the engine will start slowing it down.
Now if the gas actually isn't expanding when the exhaust valve opens and is indeed being pushed by the piston as it moves up, then that piston is being pushed by the next piston on a power cycle at that time. So if you attach a parasitic scavenging device on the exhaust stream, you will actually be using power from the next piston on the power stroke. That power could be used to drive the load on the engine.
I don't know if there would be a net power increase with your idea. Just offering some radom thoughts.
Thread
Thread Starter
Forum
Replies
Last Post
Riffraff Diesel
Vendor Specials, Discounts, Product Announcements & Group Buys
5
Jul 15, 2009 10:34 AM
