I came to this site wanting to learn more on my MB.And hoping to help others with my mechanical experience.
This started on someone elses thread.And I'm hoping to clear up misunderstandings with this one.Especially if the misunderstandings are my own.So here goes.
A four stroke piston engine of currant design is about 33% thermally efficient.While a two stroke is slightly less at about 30%.While a jet engine directly utilising heat for purposes of thrust is extreemly thermally efficient.

Due to parasitic power loss a four stroke piston engine achieves maybe 25% mechanical efficiency.(educated guess)
A two stroke engine would be better,at maybe something like 38% mechanical efficiency.(educated guess)
A rotory engine would be best.I believe they are near 40% in mechanical efficiency.
A jet engine is extreemly low in mechanical efficiency,unless it is of the turbine design which directly takes mechanical advantage of the thrust being generated.

A two stroke engine is only about 27% efficient in combusting gasoline.And around 29% efficient in combusting diesel fuel.
A four stroke piston engine is about 30% efficient in combusting gasoline.And around 37% efficient in combusting diesel fuel?
A rotory engine is about 29% efficient in combusting gasoline.(due to compression losses on the ends of the rotor.)
While a jet engine is somewhere in the 90% range for efficiently combusting fuel.

This is where I'm starting this discussion.If any of my information is flawed,please tell me so.

Now I come to the point where most people were misunderstanding me before.The primary reason for automobiles having catalytic converters and air injection systems into the exhaust is to burn the roughly 70% unburned hydrocarbons leaving the cylinders.Once past the converter,the fuel is over 90% combusted.But in the exhaust system,you get 0% energy gains.Some claim you can't burn vaporised fuel.That it can't be ignited with a spark plug.But the fact is you can run an engine on propane and methane both.They are both vapor fuels.A jet engine uses high speed air flow to mostly vaporize it's fuel.Which is high grade kerosene.I realise that an internal combustion engine can't run on completly vaporized gasoline because of tar and varnish residues left behind after complete vaporization.

In past times.It was believed you couldn't run a fuel air mixture in a carburated engine any leaner then 13.5:1.Any less would cause damage,and it did.Then electronic fuel injection came along.Instead of partially misted fuel from the carburator,we now had well misted high pressure fuel leaving the throttle body injectors or manifold injectors at a ratio around 14:1.Leaner mixture,same power,same combustion tempratures,but better combustion efficiency.Now we have direct injection of the misted fuel directly entering the combustion chamber.Having no chance to seperate in the intake stream anymore,we now have fuel air mixtures in the range of 14.5:1 and 14.7:1.
The combustion efficiency has been improved again with very slight thermal increases and slightly more power.

As fuel delivery systems have improved the quality of the fuel entering the combustion chamber,combustion efficiency has been improved.I know there are a great many factors involved in the overall efficiency of an engine.But I am trying at the moment to point out the combustability of gasoline fuel within a given engine design.To increase gasoline fuel percentage utilized,is in this case nothing more then the percentage of fuel burned in the combustion chamber.To know the percentage of fuel combusted in the cylinders,you would need an exhaust gas analyzer.And the EGR valve would need to be disabled,as well as the air injection,and the catalytic converter removed.

The only thing that would be proven analizing a car with all emission controls intact,would be the combined combustion efficiency of the engine and emission controls togather.

i missed the earlier discussion. is it worth looking up? what is the name of the thread?

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I agree that the catalytic converter gives no power gains.

I must respectfully disagree with the 70% unburned figure out of the engine.

If the exhaust contained 70% unburned fuel, the catalytic converter would be burning MORE fuel than the engine. If this was true, the converter would thus reject more heat than the engine, and probably burn up the car in doing so.

I will try to find the unburned HC figures before and after the converter.

If you are referring to my post, I said that a spark plug cannot ignite a 'lean' fuel/air mixture. I didn't say anything about 'vapor' one way or the other.

A gas turbine engine injects kerosene into a combustion chamber. The air in the chamber has to be slowed down enough that combustion can take place.

I will agree that a carbureted engine cannot run with a fuel/air mixture that is as lean as a fuel-injected engine. Yes, direct injection gives even better control, and it can be even a bit 'leaner.'

[Deleted by editing, erroneous information]

Engines today can burn a bit 'richer' to produce power, since they leave the cleanup of emissions to the cat. Too much unburned fuel, such as a spark plug that does not fire, will allow too much fuel into the converter and it will overheat.

Best Regards,
Jim

If you wish to be taken seriously, you MUST post verifiable information instead of your 'educated guesses' and beliefs. In other words, do your homework, look up the information, learn it, then form your opinions accordingly. It is far too tedious a task to enter into a discussion where 'guesses' are elevated to fact status. Especially when, in the face of irrefutable information to the contrary, you cling to your guesses and beliefs with the tenacity of a pitbull clinging to a porterhouse steak.

__________________
1989 300 SEL that mostly works, but needs TLC

Personally,

I do not like Catalatic Convertors, Here in the Uk if we want more power we remove the cat and have a straigh through exhaust fitted

Noisy but about 15-25bhp increase

Dont know if thats really realated now

This is the piece of info I'm having a problem with. Is it your understanding that a 4 stroke gas engine only burns 30% of the available fuel in the combustion chambers, and that 70% is unburned and goes to the catalytic converter or the environment? If that's what you're saying, I would respectfully ask for the basis of that information. I believe you have some incorrect information. I could not find a reference for the normal percentage of Incomplete Combustion in a 4 stroke gas engine, but I have one reference that states it is "very small." My best guess is that the amount of unburned fuel leaving the cylinders is a couple of percent or less. I suspect the 30% value you are quoting is an approximate value for the overall engine efficiency, including combustion, mechanical, and thermodynamic efficiencies.

It may well be that I've misunderstood the 30% efficiency I've read in several places.Maybe the number was supposed to represent overall efficiency,and wasn't clearly stated.But this is what I wanted.Someone telling me where I'm wrong.Not just dismissing everything.If I've made a mistake,I want to know where it is.Thank you.I misunderstood overall efficiency figures to represent combustion efficiency figures it seems.But other then that,am I in the right ballpark in understanding the other basic comparisons with different types of engines?
Tom W.the thread that origionated this was "Regular instead of Super!???".
It started about fuel saving ripoffs.I described the most common one that keeps popping up useing magnets on the fuel line,and brought up two vapor carb designs I know of that seem to work fantasticly.I got ridiculed some and got very frustrated over the matter.I admitted that in my opinion,at least 80,000 miles worth of testing should be done before anyone could say any vapor design can be said to work exactly as claimed.Now I'm trying for a good discussion of the three main factors determining engine efficiency.So far so good.
I'm currantly suffering due to broken back and fractured neck pain,which makes concentration difficult at times.So I'm sorry to all here that I can't remember exact numbers alot of the time.Or where some of my info originated anymore.But I still remember all the basic theories.And I remember all the applications to my many years of experience as a mechanic.That's why I can't make exact quotes for you here in most cases.But I'm not ignorant either.And I'm more then willing to learn what I don't know,or be corrected where I may have confused some facts.

1. a 14.5 to one ratio is leaner because the larger number is for air.
2. a 30% effecient engine only makes 30% worth of mechanical energy from 100% of the energy in the fuel. that does not mean that 70% of the fuel is unburned. i would guess that that number is way less than 5%.

sorry to hear about your broken back.

my $.02

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

catalytic converters get vey hot, 400 C I was told. Given, they are not water cooled, only air cooled. But. If I took out the cat and replaced with steel tubing, would it also reach 400 C? If not then it would mean the cat converter is actually "burning" something present in the exhaust fumes.

From what little I can remember it uses some metals/alloys/ceramics to react chemically with the exhaust fumes and trap some CO or NO2 gases??

If your old one is plugged up............maybe.
Never seen a converter yet that " costs " more than 5 hp.

Furthermore, of ALL PLACES, to remove a catalytic coverter in Great Britain, or anywhere else in Europe, is socially & environmentally irresponsible.

__________________
2007 C 230 Sport.

NO.
Because you would eliminate the " Catalytic Action " of the converter which generates these temperatures, & therefore the temperature of the replacement pipe would be much cooler.

__________________
2007 C 230 Sport.

Tom W, thank you, I remembered and spoke incorrectly. I said fuel/air ratio but industry uses air/fuel number. My bad.

The following is a link to an interesting article about measurements taken at various operating stages of a catalytic converter. Shows various inputs and outputs, under start-up, normal operation with and without the air injector pump, and operation with 1-cylinder misfire. I was interested in the HC numbers.

http://www.asashop.org/autoinc/oct97/techtotech.htm

Best Regards,
Jim

burns the fuel residue in the exhaust. it is a ceramic element that gets very hot and then burns things. some wood stoves also have a cat in their flue. it does the same thing and eleminates pollutants. in this case the heat given off is useful for heating the house.

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

After the past few hours trying very hard to remember,it came back to me.The numbers I have been using for combustion efficiency were stated as exactly that in military training manuals.I guess considering the source,I shouldn't be suprised if the information was given wrong.Now I'm going to go back up the page and look at that link on HC readings,maybe find out how wrong the military is again?Hahaha.I had formal training before the military,but of course they had to train me in the "correct" way to perform automotive repairs.

i dont think you remembered all that wrong, you just got a few terms a little mixed up. dont feel bad. i certainly do that enough.

my dad always said "if you arent making any mistakes you arent doing much!"

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.