Exhaust heat recovery- Exhaust to water exchanger

[4x4_Welder]

As a gas cools, it contracts, and through this becomes more dense.  This increase in density gives more resistance against the walls of the pipe, and slows the whole thing down. 

[buickanddeere]

  You wouldn't be able to measure the difference in exhaust back pressure at the engine if the gas temp at the outlet of the hx was 100F or 400F. And certainly engine operation wouldn't change with the gas temps at the hx outlet.
  This sounds a bit like the story where "an engine needs back pressure to operate". Ain't true.

[Firebrick]

Buick,

"an engine needs back pressure to operate". Ain't true

An engine does not need back pressure to operate simply run, but a lot of engines need the exhaust sized correctly to operate at peak efficiency at certain rpms. I wouldn't term it as back pressure but as others alluded to as velocity, tuning the length can have some serious gains as well in very high rpm engines to pressure wave scavenging.    Any dyno operator can tell you that changing the exhaust will move the power band for better or worse.  Most of the time a large exhaust will lose power in the lower rpms where vehicles operate the most and gain near the top end.

[buickanddeere]

  The engine will not run better with tuned pipe at the ideal velocity. If the pressure wave reflection is hitting the exhaust port while the exhaust valve is open. That's back pressure.
  Now with a tuned pipe giving sub atmospheric pressure at the exhaust port when the exhaust valve opens. That's a performance improvement and it ain't back pressure. 

[Doug]

People get confused because of tuned exhaust on 2 strokes where you actualy have back presure and it provides a power boost.

[aqmxv]

People get confused because of tuned exhaust on 2 strokes where you actualy have back presure and it provides a power boost.

...if the backpressure is at just the right time.

On a piston-ported 2 stroke, the reflection wave from the exhaust system, if tuned just right, can provide some supercharge.  Basically, the system works like:

1) inhale mixture through carb into crankcase (extra points if there's no reed valve - enigne is fully piston-ported).
2) blow mixture through transfer ports scavenging remaining exhaust gases out the exhaust ports.  If your volumetrics in the intake cycle work out well, you can blow a little more mixture out the exhaust port than the cylinder will nominally hold.
3) piston starts to come up, closes transfer ports
4) reflected pressure wave crams the excess mixture and a little exhaust gas back into the cylinder
5) the piston closes the exhaust port.

it makes for an incredibly peaky engine, but it can make for better power, better fuel economy, and increased knock resistance (because of the EGR).

[mobile_bob]

tuned exhaust, expansion pipes, and all that stuff
all in all a waste of time on a listeroid, and for that matter most any diesel engine.
too many other limitations to even think about going there
bob g

[buickanddeere]

  I agree that attempting to tune a Lister or Petter with resonant pipe would be more luck and money than good planning. It does however pay if required to use smooth sweeping bends rather than 90 degree domestic water pipe elbows.
  I for one enjoy the exhaust note of a slow speed diesel with a very long straight  pipe and a muffler tuned to the application.

[Quinnf]

You can eliminate some of the peakiness if you have the diameter of the pipe increase with length.  I think they used to call those megaphone exhausts.  Of course an expansion chamber is the thing to use on a 2-stroke, but on a 4 where the exhaust pulse comes at half the frequency of a two, and where you've got valves to contain the charge you don't really need the reflected pulse.  So half an expansion chamber might do the trick.  Or get you arrested.  Sure would sound impressive!

Quinn

[Doug]

And if you make a mouth piece you can play it like a trumpet......

[Quinnf]

That's actually the function of the tapered  "bell" on a brass instrument like a trumpet.  The taper, which is calculated from a mathematical formula, ensures that well-defined standing pressure waves form inside the tubing of the trumpet at specific frequencies.  Were there any reflection of sound like you get with a straight pipe, the waves would become polluted and fuzzy sounding as the result of cancelling, which in an engine would raise the back pressure. 

So when someone says the exhaust note of an engine is "music to my ears," he's not far off.

Quinn

[Doug]

I just want to be the first kid on my block who can play a tune on tuned pipe......

[sid]

Quinn// most engines are music to my ears but-----for pure noise ,you must hear a maytag or fairmont...http://www.youtube.com/watch?v=ap4x8HvQX0k&feature=relatedhttp://www.youtube.com/watch?v=wEzSCld1zFo//sid

[Doug]

I prefer the Johnson "Iron Horse" myself, but I never actulay saw what kind of washer they were used in.
Any idea Sid?

http://ca.youtube.com/watch?v=OQtYIMhgFMg&feature=related

Running a little too fast for my taste....
I had this exact engine, past tence ( so stupid of me to let it go )

[sid]

Doug// I have an iron horse just like that one//.. it was designed to replaced the maytag because it had more h/p// the maytag was a little too small and the space under the washer was very small and iron horse made an engine with cylinder tilted to one side... also the maytag was a hit and miss but the problem was it turned off the ignition to make it a hit and miss.. so it kept intaking fuel and blowing it out the exhaust.. made for a terrible smell and not very good fuel econemy.. the iron horse was an option on the maytag washer.. the run time could be controlled by the amount of fuel added to the tank../I think a lot of iron horses was made for the military during the war//my 86 year old friend is and expert on iron horse..he has one that was in his family in the 1930s and he still runs it/// mine was made in the 1940s..// sid