An obvious question...

[Duane Oxley]

So, I'm having a discussion with my friend, Rob, the small engine mechanic yesterday. And he's telling me about how much more fuel- efficient the fuel- injected Kohlers are than the carburated ones... "Yeah, as much as 60% less fuel.", he says.

And I can't help but wonder...

I mean, there's only so many BTU's in a gallon of gasoline. So if you reduce the consumption, you reduce the available BTU's... right?

So I say, "So, they probably run cooler as well.".

"Yep.", he says.

So, the obvious question... Why would a heat exchanger manufacturer want to use one in the smaller 2- cylinder motors...? They have to reduce the output heat capability... by a substantial amount...

 

[406]

i dont know but, what temps could that gas saving motor supply?

 

[hogjowl]

I have never owned a heat exchange unit, so I have no idea how they work, but don't they capture the blower heat, as well as the motor exhaust?

 

[Greenie]

Duane has an excellent point.

For a small HX system, I want to burn some fuel, it's where it all starts.

 

[Shawn Forsythe]

The answer lies in what is actually happening to the fuel. Measuring the amount of fuel that passes through the engine is not a dependable means of ascertaining the net BTU output of the motor.

An inefficient fuel system contributes to a less than complete burn in the cylinders, which just means more incomplete or unburnt fuel is expended through the exhaust system. This unburnt fuel contributes nothing to the BTU output of the engine, it just means wasted fuel.

Now, a certain amount of the incomplete combustion BTU's can be recaptured for our purposes of heating, with a catylitic converter, but only the CO component with any great efficiency. Carbon particulates are much less burned in this process. You are actually going to do a better job with complete combustion, in the chamber, with a fixed HP output.

I doubt that a FI system runs appreciably cooler, in the actual exhaust flow. In fact, a lean burn will actually create higher exhaust temps, but it doesn't mean necessarily more BTU's. One has to understand that you can have equal BTU's, even with an temperature difference of a gas, because the actual volumes or pressures may differ, thus creating an offset compensation.

With the crank output equal, the cleaner burning engine will likely create more available BTU's at the exhaust port, as less wasted, unburned fuel will be present in the form of carbon particulates.

 

[hogjowl]

So, I guess the first step in answering the question is to determine if a FI engine actually DOES run cooler.

Would somebody answer my question about capturing blower heat?

And how much does it contribute to the overall heat output?

 

[Duane Oxley]

Mardy...

In most HX systems... the mid- to higher level ones (as opposed to most so called, "entry- level ones), you're right, the blower's heat is used.

In some systems, it's a pre- heater for the pump's bypass loop. In others, it's a "modulator" for the output from the exhaust exchanger. In other words, it's virtually never a "primary" exchanger, meaning that it's not the hottest and doesn't have the most available BTU's available. The motor exhaust is in the 1,300- degree range, compared with the blower in the low to mid 200's.


Shawn...

I'm aware that the more lean the burn the higher the temperature... And that's one of the things that always nagged at me, in considering heat exchange systems, due to how some guys run their systems ragged... doing "maintenance" only when it starts running poorly. (Not doing a tune up... changing plugs / adjusting the gap, not changing the air filter / cleaning the pre-cleaner, etc., makes it run richer... which 1.) runs "cooler" and 2.) soots up the exhaust exchanger, which reduces it's efficiency...)

The thing is, the way I see it at the present (I'm open to seeing it differently, if figures say so...), given the same CFM output, a carburated system would have to "burn" at 50%, or thereabouts, "lower" temperatures (or a FI system would have to burn 50% hotter, etc...), in order to offset an increase in efficiency that a fuel injected system would provide...

Am I missing something here...?

(By the way... I addressed the sooting thing in the design that I've been working on...)

 

[Mike Brummett]

Shawn said what I was gonna say!

MIKE :wink:

 

[The Cleaning Artist]

On a carb engine that is under load, a slightly rich mixture (air/fuel) will actually cool the cylinder and exhaust temperature. If you go too rich the fuel will actually burn in the exhaust system and cause extremely high temperatures in the exhaust. With a FI engine, the ratio will stay the same and I would say the exhaust temp would be more as the engine can and will be ran leaner.
I will say that our small engine HX SteamAction machine will push 270-280 all day long while cleaning with one wand and 230-240 with two wands.
My guess would be no change from identical machines from carb to FI except better fuel economy.

 

[Duane Oxley]

Harley...

Once you start mentioning temperature output in the cleaning solution, whatever you say is irrelevant without the context of flow rate at that stated temperature...

So the question is, "at what flow rate?". If you don't know the rate, you can take a pretty educated guess at it by determining the jet size and pressure you run at when those temps are reached...

Also... what size motor / blower and are both used to generate heat, etc...? All that has to be taken into consideration, if you get outside of speaking of principles at work and get into specifics...

 

[The Cleaning Artist]

How's this?
wand 1 = two 03 jets @ 400 psi with an 80% duty cycle
4007 blower
27hp
4 heat exchangers from 2 sources, blower and engine


two wands = 4 03 jets

 

[Scott Rogers]

Duane, check your private messages.

 

[RichardnTn]

A gallon of gas will only produce a certain amount of BTU's. If a motor is more effecient then it is producing less BTU's because it is burning less fuel. BTU's translate into friction, heat, horsepower, unburned fuel either as soot or unburnt gases out the exhaust... Even the heat that the blower exhaust produces figures into the equation of how many BTU's are in that gallon of gasoline. Any heat, primary or secondary is a consequence of combustion, either directly or indirectly.....
Best to all, Richard R

 

[Duane Oxley]

Harley...

If you use 1/4" hose, then you're losing about 150 to 200 PSI, at the end of 200 feet of it...

If you take 300 PSI through a #6 jet equivalency, you get about 1.2 GPM, if memory serves...

 

[The Cleaning Artist]

I will test tomorrow @ 100 ft and 150 ft with 400 psi for gpm.

Not sure but with two wands going we dump about every 45-50 min @ 110 gallons recovered. 2+ gpm