Ceramic Adiabatic Engine 2

[SterlingPower]

Hello again all

Upon further research the main effort seems to be fouces on improcing the combustion effiecny of the engines, but there doesnt seem to be that much of an effort with trying to extract the energy in the exaust, a catalyst after all is to burn the unused fuel.

With an adiabatic engine, the combustion in the cylinder is raised, so the thermal effiecency is greater, so the emissions unforutantly also increase with the temprature,
is there a reason why this idea hasnt been further adapted?
Water and coolant that could be cycled around the exaust to create a cooler gasses and used energy to return to provide steam for a crankshaft piston?

The main point here, is the article Ceramic Adiabatic Efficency

http://www.sof.or.jp/en/activities/pdf/06_07.pdf

These modification seem to be the ideal solution to the quest for effiecny,

so im like to know the cost of engineering ceramics,
why they are costly,
and wether somthing like above could be done with an experimental engine,
also, even thgouh this is an efficent engine the emissions would be a problem I assume?
and again im always interested in others opinions

Thanks

Sterling Power

 

[MikeHalloran]

High combustion temperature in pursuit of Carnot efficiency was all the rage until NOx was perceived as a real problem.

;---

Technical ceramics are expensive because they're hard to make, and the process is inherently slow.

They're hard to make (with accuracy) because they have to molded or formed substantially oversized in order to get the size or shape you want after drying. Substantially in this context means 20 percent or more oversize.

The process is inherently slow because the drying stage, where the shrinkage occurs, takes 8 to 12 weeks, and can't be accelerated because of the shrinkage.

Continuous production also gets expensive because of the real estate required for the in-process inventory. A video occasionally shown on PBS follows the process of manufacturing vitreous water closets. They dry while being towed along on a chain conveyor that moves at barely perceptible speed, and is on the order of a mile in developed length.



Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

SterlingPower,

An adiabatic IC engine implies that there is no heat transfer from the working gas during the cycle.

While low thermal conductivity ceramic parts such as piston crowns, combustion chamber liners, exhaust port liners, valves, etc. can minimize the heat transfer rates during an engine cycle, at the same time they also cannot create the necessary thermal environment needed for long piston ring life. All of that thermal energy focused in the combustion space only increases the heat load at the piston's top ring.

The reason piston rings last as long as they do, is due to the perfect boundary lubrication oil film conditions created by the oil control ring and the properly cooled cylinder liner surface and ring lands. If the cylinder liner bore surface is not cooled to about 350degF or less, the perfectly thin oil film left on the liner bore by the oil control ring will flash off, and the piston rings will scuff.

The end result with adiabatic engines is typically just higher exhaust temps, and not better efficiency.

 

[BrianPetersen]

On an engine using premixed air and fuel, high surface temperatures will feed heat into the air/fuel charge and thus promote detonation in the end gas. The countermeasures are to either (A) lower the compression ratio, thus lowering cycle efficiency, (B) retard the ignition timing, thus lowering cycle efficiency, or (C) use exotic fuel chemistry - not a viable option for a road vehicle.

With a diesel engine and with certain other direct-injection concepts, detonation is not an issue, but it's still a tough application as noted in previous posts.

You cannot avoid heat transfer between the surface and the gas - raising the temperature of the surface might reduce heat transfer out of the gases in the cylinder during the high temperature part of the cycle but it increases heat transfer into the gases during the low temperature part of the cycle (intake and first phase of compression stroke). Whether this is a net benefit to cycle efficiency - assuming that detonation is not an issue - is a toss-up. The lubrication situation is a big problem. So is the NOx situation.

Using thin heat-reflective ceramic coatings on selected surfaces in the combustion chamber - while still maintaining proper cooling of the cylinder walls and pistons and head! - is a viable option. It's still open to question whether there is any net benefit to cycle efficiency and performance but it CAN extend the life of pistons in tough applications. There have been piston coatings used in OEM applications (I seem to recall reading that some Subaru turbo engines have coated pistons) but the lack of universal application suggests that it's not something that's worth doing unless it NEEDS to be done.

 

[patprimmer]

The Toyota 7M-GTE also had coated pistons.

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers &

http://eng-tips.com/market.cfm

for site rules

 

[evelrod]

I've used "coated" pistons in the past. Never saw any advantage over std. Not cost effective for my applications.

Rod

 

[j2bprometheus]

Hi-

There have been several adiabatic engine projects in the past.

Example: Cummins had one in the 1980's.

Google this:

R. Kamo W. Bryzik

There are some SAE papers. Example:

"Adiabatic diesel-engine technology in future transportation " by Roy Kamo.

There is a company pursuing adiabatic engines founded by Roy Kamo that his son Lloyd Kamo now runs.

I remember back in the 1980's that Toyota claimed it was going to have an adiabatic engine in production in five years. I am still waiting.

By the way, the combustion efficiency of a modern "conventional" diesel engine is already above 99 %. So improving combustion efficiency is NOT a motivation for having an adiabatic diesel engine.

Adiabatic engines would have rather hot combustion chamber surfaces. This lowers the volumetric efficency of the engine, based on intake manifold conditions. The result is lower power density, which offsets some, all, or more than, of the potential power density gain due to lower heat transfer losses.

 

[naturalextraction]

"a catalyst after all is to burn the unused fuel." Just a note to that statement. It would be more like the exhausting of spent hydrocarbons and wasted heat energy. With modern cars all the fuel is utilized in the combustion chamber. There is an issue as to how much of the internal chemical energy is utilized to do work in that environment. Heat energy is best utilized in the combustion chamber with gets into the adiabatic flame temperature and the equations related.
Another book you might look into is "The Romance of Engines" by Takashi Suzuki, Ph.D.
Published by: SAI Society of Automotive Engineers, Inc.ISBN: 1-56091-911-6 (hc)
When he worked at Hino Corp they had as close to a truly adiabatic engine as can be expected at the time. It's a good read all around for this topic. Very well put together.

 

[jmc41]

With diesel engines, both two cycle and 4 cycle, manufacturers have found that heat does not increase NOx. In fact most have increased compression ratio to reduce NOx.

The issue is how to start ignition as soon as possible after start of injection. The shorter the combustion delay the lower the NOx and the more injection can be advanced to reduce fuel consumption.

Have tested ceramics in 2 &4 cycle engines, small bore and medium bore size. The thick pieces crack so easily tests were short. Spray on coatings, although not fragile are not always durable. Tests on all engines showed about 1 to 2% higher fuel consumption with no reduction in NOx.
It reduced mass air flow thru the engine.

On one relatively long test, at disassembly, we found some flaking of the coating in hot areas.

I totally agree with the previously stated requirement to keep liner temp below 350 deg. The only exception is if plasma coated top piston rings are used.

rusty1856@msn.com

 

[SterlingPower]

Hello, I was wondering if ppl have looked at the pdf document as it illustrates that there is exaust gas recovery systems that arent seen on engines nomally and additionally its fuel was natural gas rather than diesel. This achived on the order of 68% thermal effecieny. Whilst the base effiecny of the engine was around 40%, im suspecting a good reason why this hasnt seen the light of day, noteably the study was done in 2000 which was a while ago..

Cost again and scale of production im seeing as the stumbling blocks, however those books I certainly will be looking at though

The general idea i belive is utilising a higher cylinder temprature which gives more energy in the exaust to use, which seems good in thery, maybe with modern technology this can be proven to a more acurate level?

Apreciate the comments and contributions

 

[BrianPetersen]

I'm looking at the file right now. My Japanese is not so good, but from the pictures, they're using linings in various locations and they're using a pre-chamber combustion system of some sort in an oceangoing vessel (i.e. this is a very large engine), and an exhaust turbine. They're quoting 48% thermal efficiency including the exhaust turbine. The steam turbine increases this to 52%. So far, all this is plausible but it has to be stated that a "normal" diesel engine in an oceangoing vessel already has an efficiency in the 50% range.

I question their steam-reforming proposal, though. Chemical reactions invariably result in a loss of useful energy, not a gain, and it doesn't seem plausible that the low-grade energy remaining after all of the above would be useful to drive any sort of chemical reaction in the opposite direction of the way it naturally wants to go.

 

[JSteve2]

jmc41, the first two lines of your last post are just not correct. I'm trying to understand if you mean something else and that's just not stated correctly, since much of the rest of your post seems reasonable.

 

[Lou Scannon]

JSteve2, you took the words out of my mouth.

 

[CCycle]

Jmc41 Thanks for the interesting post. No doubt you observed that more compression (more heat and pressure) lowered NOx. But there is more going on. One of the big things in CI engines is ignition delay. The fuel is injected then sometime there after it burns all at once giving the well known diesel knock and a high temperature peak. By increasing heat you shorten the delay which lengthens burn time and reduces peak temperature.

NOx production rate is very much a temperature/pressure thing. It is an exponential relation with temperature. The exponent is somewhere around the third power. If you were to indicate the CI engine with severe ignition delay you will see a small, sharp peak on the otherwise smooth compression curve. This peak looks insignificant but such is not the case. Due to exponential NOx production, this peak is NOx city.

Note that the efficiency of a heat engine is proportional to temperature difference. It is not exponential. Engine design has a dual problem, keeping the peak temperatures down to lower NOx, while keeping the average temperature high to get reasonable efficiency and specific power.

 

[Lou Scannon]

CCycle, those are interesting and valid observations, but in your first paragraph, the last two sentences are not incorrect but are only scratching the surface of diesel combustion and NOx formation, leaving a lot of room for misinterpretation. Care to elaborate (or cite references)?

 

[CCycle]

Hemi Agree the post isn't clear. What I was trying to say is; when a CI engine is cold it has long ignition delay. When the fuel does ignite it tends to burn all at once like detonation in a SI engine.
The rapid energy release makes for a high peak temperature which gets into a temperature range that generates nitrogen oxide.

The original post speaks of a ceramic engine. I just assumed they probably would be operating at a minimum compression ratio to try and protect the ceramics. It could be that increasing compression would spread the fuel burn hence lower peak temperature... For what it is worth.

The same day I made the first post I started a tractor. Normally when it is so cold we don't try to start them. It is too hard on the equipment but we needed to move some stuff. With the aid of a 200 amp booster and long glow plug heat it started but clanked and banged so bad I thought it was coming apart. When they run this way you get a sharp smell not characteristic of diesel. After warm up they are ok. All our equipment is old, conventional injection, not common rail.

I don't know of any papers on this topic. There is a discussion of ignition delay at;
the-crankshaft.info/2009/09/diesel-fuel-combustion.html
Scroll down to ignition delay. You, no doubt, are well aware of this.
What is your take?

 

[BrianPetersen]

The traditional concepts of ignition delay and its relationship to NOx etc somewhat go out the window with modern combustion systems. It's not like the rules of physics changed, but only that the process is being tweaked to change the outcome.

In a normal diesel engine, even when the chamber as a whole is overall lean, combustion is actually occurring near stoichiometric adjacent to the surface of droplets, at a temperature that can be much higher than the average temperature in the chamber. This leads to high NOx formation in a traditional diesel engine with a direct-injection layout.

How do you reduce that temperature -> first approach was to introduce dilution into the cylinder in the form of exhaust-gas recirculation when the engine is running at part load. Technically it is quite straightforward to do, and EGR has been used on automotive diesel engines since the early 1990's.

But there is another approach ... Intentionally delay ignition until after the fuel has substantially evaporated so that it is no longer burning near stoichiometric, but is burning in a lean manner throughout the chamber. And how do you do *that*? Homogeneous-charge compression ignition is one way but it's hard to make it work outside the laboratory. Another way is to use extremely high injection pressure so that the fuel is finely atomized, and do the injection in multiple stages. Sounds like a modern common-rail diesel engine ... or the "supercritical combustion" concept that there was recent discussion of.

As I understand it, part of the idea is to inject the first shot of fuel well before top-dead-center so that it has lots of time to evaporate and mix with the charge air. That shot of fuel burns in a premixed manner. Then you inject another shot of fuel, which evaporates much more quickly because of the now-raised temperature in the chamber but also when that combustion occurs in a dropwise manner, the surrounding environment is already partially diluted with products of combustion from the first shot of combustion. Then you inject yet another shot and this happens again. This concept is also compatible with EGR for additional dilution to get the peak temperature below the NOx formation theshold.