No Such Thing As A Free Lunch

[Dualfuel]

Ronmar,
I thought I would bring this over to a "new" topic. It is much more interesting then ranting about HHO...
Your statement about no free lunch does not apply to internal combustion engines, or perhaps it should be modified to read...
"The Lunch is not free, and we are throwing half of it away!"
I had to go back to Ricardo, page 16 of Slow Speed Engines, to find what I was looking for...namely the theoretical limit of efficiency for a gasoline (or constant volume) engine. Its also known as the Air Standard Efficiency. For pressures between 140psi to 450psi that limit is 47% meaning 63% of the heat MUST be wasted.
So if our engines are only getting around 20%, then there is another 27% that can be looked upon as fair game for improvement.
The "No such thing as a free lunch" part of this improvement are things like frictionless bearings, zero pumping losses, and adiabatic expansion. What we do have, is room to improve combustion. The goal would be complete combustion. That is why we have catalytic converters, because of incomplete combustion.
What if one day an alloy or ceramic, or a shape was discovered that eliminated quench distance? Zoom! Up goes the limit of complete combustion.
It is in these very narrow limits of one particular arcane facet of combustion, that any further improvement of fuel effciency will be discovered.
I bet if we went back over what Ricardo did, we'd find that he or the germans knew all about Hydrogen fuel properties and how they related to various gasoline/hydrogen mixture's flame speeds....
Me, I want to find a film with sound, of those giant Maybachs burning blaugas pushing a dirigible around...(yep, doing it before everybody had cars). Sorry I digress.

[Jens]

Interesting ... note though that heat doesn't HAVE to be wasted.
Theoretically speaking, if one was to inject (not sucked in with air) water in a diesel engine at the same time as fuel is injected (but obviously not through the fuel injector), would there be a noticeable power gain by turning the water to steam (and expanding)? Just curious if there can be a tiny bit of free lunch to be had ... and please note I am not talking about HHO nonsense!
Maybe one of these days we will see super efficient peltier devices to turn a lot of the excess heat into electricity but for now we can still use a lot of the heat for space heating.

[Thob]

Uhhhh....  47 + 63 = 110

Maybe you meant 47% and 53%

Anyway - somewhere I read that in a "typical" gasoline engine, the energy input is distributed as follows:
25% - crankshaft power (useful work)
35% - waste heat in the cooling system
35% - waste heat out the exhaust
5% - waste (unburned) fuel out the exhaust

so messing around with fuel injection, better burning, etc. is only working on the 5% waste.

I've also heard that diesel engines are more like 30% crankshaft power.  The increase comes mainly from changing the heat cycle by using higher compression ratio (technically, higher expansion ratio).

I've also read about some work using a piston with an ceramic insulated top.  This would reduce the heat loss into the cooling system, and should result in higher efficiency.  Unfortunately, I never heard any real numbers about the gains.  It would seem that a nice layer of carbon on top of the piston would work as well...

Anyway, I would expect improvements to come in small percentage numbers, not huge gains all at once.  And the proof has to be in real data that can verified by other people, not just marketing BS.

[Dualfuel]

Ha! You got me! I never could ad very well.

I am sorry for my earlier brevity...the number I gave, 47% is for a constant volume engine, (not constant pressure, meaning not a diesel), and is only good within the range of 450psi to 140psi, these pressures are present during the sudden burning of the gasoline at ignition, down to when the exhaust valve opens.

The main point is that this is the limit within which heat is being turned into work.  This is one of those laws, within the 47% lies Thob's percentages. The 53% is there for Jen's Cogeneration uses.

The idea of water injection, is one of those peculiar truisms about internal combustion engines. Example: Unlike other thermal efficiency processes (boilers), you cannot simply raise the temperature of the hot reservoir to increase the efficiency, the gasoline won't stand for it, and will detonate, nor will the metal on the cylinders, rings, and piston, not to mention the lubricating oil.  Turns out that using a lower temperature in the high temperature reservoir, is the actual way to get more thermal efficiency from a constant volume engine. Like Jen's referred to, if a portion of the clearance volume is occupied by atomized water, and the rest by a air/fuel mixture, then when ignited, the heat is absorbed by the water turning it to steam. The specific heat of air is very low, while that of water is extremely high, meaning the air cannot absorb the heat with out its temperature climbing rapidly, while the water/steam can absorb a great deal of heat without a rapid temperature rise. The water to steam volume change is 1600 times, so even if the peak combustion temp isn't very high, steam's expansive force is making the pressure rise high enough to offset the low temp.
The point about air standard efficiency, is that it represents the limit of what you can do with fuel and dry air in a cylinder, and its good to know, because it allows one to understand that its all about BTUs and things like Fish Carburetors, GEETs, and what not, cannot work because a certain number of BTUs are needed to make the pressure in the cylinder, and a certain amount WILL be wasted. As far as constant volume goes, there is no over unity, nor is there even half unity.
Yet another tidbit...the modern gasoline engine doesn't even use constant volume, only hit and miss engines are using constant volume.

[Dualfuel]

More on constant volume, because I realize we gotta get the definitions straight in order to perfect our understanding. Constant Volume is not the physical space inside the cylinder, but rather the material occupying it. If you have a 23D Briggs &Stratton, then your physical volume is 23 cubic inches. The air/fuel mixture's theoretical limit is 23 cubic inches. In practice you do not get 23 cubic inches of gas inside the engine because the piston is moving too fast for the air to travel into the cylinder and fill it, AND a B&S engine is throttle governed, meaning it has a built in restriction crippling its power output....the butterfly valve in the carburetor. The only way a throttle governed engine becomes a constant volume engine is when you remove the butterfly, and we know how long they last when you do that.
Here is an example of a constant volume engine, it has no butterfly, meaning each time it fires a charge, its the maximum charge that the atmospheric pressure will force into it. To stop such an engine from destroying itself, the governor simply turns off the air pump by leaving the exhaust valve open and shutting down the ignition, allowing the engine to coast on inertia until the rpms drop enough to reengage the exhaust valve and ignition. The other effect this has is thoroughly cleaning out the spent gases.

https://www.youtube.com/watch?v=YUE4KwOsAIw

[Jens]

So does that mean there are gains to be had by water injection?
Unfortunately, all the other technical talk about theoretical efficiencies etc are way beyond me

[Dualfuel]

Dear Jens,
I will get back to you on the water thing. I will say this, water injection was an option GM offered in 1954 on medium duty trucks. It was also part of WWII fighter aircraft engine's (although they used an alcohol mixture to prevent freezing. )
You must understand, I want to phrase everything very carefully here, a simple yes doesn't cover it. There are conditions, and most have something to do with detonation caused by flame fronts having a real long way to travel, or odd shapes, sharp edges in the combustion chambers.

[mobile_bob]

water injection on its own will not increase efficiency or power, it can't!

reason being is this

internal combustion engines are heat engine's, the heat of combustion is what drives the piston
now we can either use all this heat to drive the piston or we can use a portion of the heat to vaporize
water to steam to get an expansion effect.  it in theory still ads up the same, however it in practice will result
in lower power.

the reason it works to make more power, is this
it enables an engine to run at higher compression ratio's without detonation because it lowers the heat in the cylinder, it can also allow for more advanced timing, either separately or combined.

but on its own all things being equal it will not produce any more power, it just cools the intake air to allow for more advance or compression ratio increases which are the reason for the increased power.

if you take an engine with a fixed compression ratio, and set the timing for peak power without detonation and then admit water injection you will net no additional power, and in reality you will see a reduction in power.

as for expansion of water into steam driving the piston... there is just not enough steam to drive much of anything, because there is so little water being admitted.. admit enough water to provide for significant expansion and you put the fire out in the cylinder.

as for gains in efficiency,  unless you have a very sophisticated test cell, a large research capability, high tech instruments and tooling, very expensive materials, and a phd or three... look for gains in the sub 1% range for very good engine designs and certainly less than 5% on antique designs as being within reality.

you just can't get there with engine's designed and built with 1930-1960's technology and materials, and i don't give a crap who you are.

ricardo was a very bright fellow, and there are other such as charles fayette taylor of MIT for instance... i would strongly suggest doing a lot more reading and study before betting the lunch money on anyone coming up with some 47% efficient engine in the sizes we are able to use.

think about it guys!

does anyone think companies like honda, gm, navistar, cat, stihl or whatever can build much higher efficiency engines but choose not to?  why not?  with billions of dollars in sales at stake, market share?
these companies and others have the brightest minds on the planet, the best equipment, the best materials, and a vested interest to be the best in their industries... and what we have is the best that can be done at this time...

and i am to believe that some guy in his garage is going to beat honda at their game?

like grandma used to say   "maybe so but i friggin doubt it"

this is a cogen site, far better to accept the efficiency of the engines we have to work with!  because?
the waste product is heat? right?   and we can harvest it, right? and use it?

far better to spend time working out how to harvest this waste heat and effectively use it, that is where the real  and attainable gains in efficiency will be made.

dollar for dollar, hour for hour, the best return on investment is the harvest, recovery and use of this waste heat, probably 1000:1 in favor of this over trying to eek out even a percentage point or so out of the engine in mechanical power.

good luck

bob g

[Jens]

Bob, no reason to get your undies in a knot I have no idea about engine physics at that level and it was just a question that sprung to mind. What you say makes sense ... heck, anything makes sense since I am just not at that level. So, question asked, question answered, let's move on

Oh, re commercial engines using water injection - If you had a small gain in efficiency but at the same time you add $100 in costs ($1000 retail) plus you add complications that most people don't want to deal with, then maybe it isn't viable to add that to the overall car system. Actually scratch that - if you added injection you would need a high pressure pump and metering system and your cost would be well into the thousands with retail being ten times that (I am assuming here that you need to get the water into the cylinder after combustion starts and certainly not during the intake stroke as the water would evaporate before the intake valve closes.)

Anyway, never mind, just running the idea up the flag pole and now we have an answer. Thanks Dualfuel and Bob!

[glort]

There are 2 interrelated reasons why Water Injection isn't used on modern Vehicles. Neither of them is cost.

One reason is that it is impractical to carry enough water between servicing for what the vehicle would need.
Other reason is that you would add WI to allow you to run higher cop ratios, timing whatever to get better power/ efficiency out of the engine.
If the water is used up, then the engine management would pull back the benefits the WI gave and you'd be back to square 1.

I also believe there is legislation in some countries at least that an engine must maintain it's emissions for a certain time if not the life of the vehicle.  Tune the engine for water and it runs out, your emissions profile changes as well. Sorry, Can't sell that car in this country!

The thing is, manufacturers can't rely on owners to do anything other than put fuel in their vehicles.  So many owners these days  never lift the bonnet themselves between servicing. They just want to get in it and go and putting in fuel is a necessary evil which is about the limit of their capabilities.
Ask them to put water in and there would be water in the fuel tank and vice versa on a scale people here would probably find hard to Imagine.

Not sure if you have it in the states but a lot of Euro 5 emissions trucks run a solution called Adblue. This is a urea solution that is injected into the EXHAUST of the trucks and cleans up the emissions, specifically NOx. All these system are computer controlled and when the computer senses the Adblue has run out, it throttles the engines power back to 50% to save emissions and encourage the driver to refill the tank.

People would have a fit if their car did that although I think it would have to limit the power to about 2% for some people to notice.

I have a friend that works in an outer suburban, IE, Small, Dealership.  He gets 5-10 cars a Week coming in that have been Misfueled.  Good for him and I using said fuel for blending in our veg oil but quite a worry when you realise how many people muck that simple thing up. 

Engines can and are tuned in racing applications to take advantage of WI and squeeze more power out of them but unfortunately manufacturers can't design a system where the things fill themselves with water and that is the achilles heel of WI in common automotive useage. 

[Ronmar]

The main benefit of WI is as a chemical intercooler.  Either for higher compression engines, or turbo/supercharged(boosted) applications.  I believe that was their main WWII use in aircraft engines running massive ammounts of boost but no room in the fuselage for the massive intercooler required to counter the heat effects of air compression.  It is also used in gas turbines, the most noteable being the harrier which has a 145 gallon tank of water/alcohol mix used for peak power.  It uses this in about 30 seconds:)

[mobile_bob]

Sorry Jens, my point was not to ruffle feathers, or come off harsh
its just been a really bad few weeks for me

my dad had been sick for the last 2.5 weeks leading up to his sudden death last wednesday morning
then we got word the very next day that my wife's dad passed away barely 30 hours later! 

we buried dad yesterday, and my wife is due to leave for california to settle her dad's affairs this morning.  we sleep around here, but we don't seem to be getting any rest.

when it rains it pours, or so it seems
all this will pass, i am sure, but it doesn't make it any easier while one is going through this sort of thing.

i came in on here to sort of take my mind off the issues here at home and probably should have taken another avenue for escape rather than come off too sharp/harsh for the membership.

sorry guys

bob g

[SteveU.]

Good Morning Fellows
Yes glort there have been USA Federal Gov'mint EPA restrictions AGAINST any supplementary operator needed to add liquid systems other than the base fuel since the late 1970's. They KNEW people would not comply and continue to run. Since then up until ~2003 the Manufacturers were required to make all systems that were primary emmisions controlling durable/stable for 5 years/50,000 miles. This drove the change over to first to electronic ignition; long life ignition componets such as dist caps, rotors, plug wires. Later this standard was changed to 8 years/80,000 miles. Then is when the distributorless systems were develope; the platimun and iridium tipped spark plugs and the 100,000 mile life timing belts.
Small engines got folded into emmisions Life compliance guarantees based on service life hours. 150/250/400?500? hours.
The 2007 and later on road diesels here were finally allowed to have the "cat piss" urea post engine injection systems as an Exception in return for lowered NOx and soots guarantees and THAT is what drove the need for going with ultra low sulpher (expensive!) refined fuels then. AND as you point out - road diesels by then electronically FI controlled could then force auxiliary systems compliance refill by forced power cut-backs and limp-in running just as the road Auto gasoline have phased in has since the 1996-2003 time period.

Yes as a former Master Auto tech misfueling eIther way I've seen cause misfiring, poor engine running and even burnt off spark plug tips.
DO NOT treat a dedicated designed low or mid grade gasoline system to a tank of premium gasoline!!

Jens and others water injection and misting into any engine can have some limited power benefits under certain limited conditions. To sort out and restrict this use to those limited beneficial conditions requires either a very knowlwgable operator or a pre-programed and multi-sensed electronic control system.

I'm 100% with Mobile Bob on this. IF there is any add on system or even base engine design that would be benificial one of the international primary engine manufactures have tried it and would be using this with thier firece market competitiveness.
Those who think something really usable is just out there in some fellows garage;  or hiding in patents somewhere have NO SENCE OF TECH HISTORY AT ALL.
On IC piston  engines OTTO's system evoled out to be the winner 1860's to 1890's as the simplist, most durable, effective why to get the job done.
Herr FelixW after 30-40 years of promoting his "simpler" system got a lucky very short history period break when late 60's we still thought we could ignore fuel effincency and emmisions for power to weight to size factors. That came crashing down quickly in the mid-70's taking out a couple of  manufactures with the realties that an only low compression capable, single ring/wiper seals, large squish area system was not going to be able to match overall perfomance tech of you pick: 2, 3, 4, 5, 6 per piston sealing rings; compression ratio dial in; widly variable actual cylinder volume/speed tuning; and the separatly camshaft driven modifiable vlaving possible in IC piston engines. Many of the same Reasons Why IC piston engines displaced out tractive steam: better fuel use effincencies, much lower maintences and much less human labor dependent per operating hours.
Tech history lessons WHY we are still using metalic firearm cartriges 150 year later after thier 30 year refinement shake out period in this same late 1800's time period. 50-60's Gyro-Jets and 70's to current consumable "cartridge-less" systems suck in dry dusty desert; wet, wet tropic; and variable wet then frozen Arctic conditions.
You can take this down to the current chic reinventing down to shovels and hammers. How many have chucked out their current eveoled wooden handled tools for the latest, greatest "Worlds Best" heavy, cold, soul-less, all steel "unbreakable" shovel or for the latest greatest "Anti-Vibe" composite plastic high tech hammer??

Hey. Just toss out all of that "old", "dated" more durable simpler stuff my way!
Favorite place to peruse? Goodwills and thrift shops in Yuppie Smart ed-u-ma-cated areas!!
Practical, pragmatic  Rurals everywhere, and every when, never give up anything still good and usable even if dated and out of the current chic "fashion" cycle.

Regards
Steve Unruh

[Tom Reed]

On thing WI may assist with, if doing exhaust heat recovery using an air cooled engine. The water may carry more heat out of the engine via the exhaust stream where it can easily be recovered. If it works as expected perhaps half or more of the fan blades cold be removed from the flywheel to get a bit more power to the crank too.

[quinnf]

[snip]

we buried dad yesterday, and my wife is due to leave for california to settle her dad's affairs this morning.  we sleep around here, but we don't seem to be getting any rest.

when it rains it pours, or so it seems
all this will pass, i am sure, but it doesn't make it any easier while one is going through this sort of thing.

i came in on here to sort of take my mind off the issues here at home and probably should have taken another avenue for escape rather than come off too sharp/harsh for the membership.

sorry guys

bob g

Um . . . shouldn't we be saying something like "sorry to hear that, Bob.  Grouse all you want to.  Considering what you've been going through, and what you ARE going through now, you're entitled."

Here.  I'll start.


Quinn