Ways to increase diesel engine efficiency?

[RustyLugNut]

I am familiar with most of the technologies linked to and would add the expansion of ideas as the aforementioned Homogeneous Charge Compression Ignition ( HCCI ). This steps into the idea of Low Temperature Combustion (LTC) concepts. By mixing of fuels and their combustion reactivity, HCCI can be extended to work in a much broader load range. This Premixed Charge Compression Ignition (PCCI) is seeing much research and possibility.

Most new engine concepts deal with improving the mechanical configuration. But, even with the traditional piston/rod/crank diesel engine, you can improve efficiency via combustion shaping. The diesel engine already has the advantage of producing more torque over the most advantageous crank angles in comparison to the Spark Ignited (SI) engine. This advantage is accentuated in modern high pressure digital injection with its multi-injection capability. The Transonic Super Critical injector expands on this even more.

As valve timing technologies mature and become more common place, diesel engines will be able to take advantage. Yes, most manufacturers as of yet do not see fit to equip diesels as such, but I feel soon, the costs will outweigh the gains. Then, diesels will be able to run in the over expansion mode, much like the Prius engines. A Colorado physicist who was part of these forums in the past did a white paper that I helped peer review. It was a mathematical modelling of an over expanded diesel engine. He calculated such an engine could approach 60% thermal efficiency in theory.

We haven't even begun to apply reduced entropy combustion schemes.

The diesel engine is a great place to start if you are a serious ecomodder. It will reward you with excellent efficiency even in the most basic of models. It will allow you to take advantage of advanced combustion theories as you move forward.

[cRiPpLe_rOoStEr]

Originally Posted by oil pan 4

Get a regular diesel engine and you have the potential to burn diesel, biodiesel, SVO as your primary fuels. And you can burn CNG, LPG, gasoline, methanol, ethanol, E85 as secondary fumigated fuels with out complex metering systems.

With a direct-injection Diesel, you can even use ethanol as a primary fuel too. Even Rudolf Diesel himself predicted that when he was developing its engine, considering the develpoment of energy-self-sufficient agricultural settlements in the German Southeast Africa (currently Namibia).

[RustyLugNut]

Originally Posted by GreenHornet

Supercritical fuel injection

Link = Supercritical Fuel Injection | MIT Technology Review

Wow seems pretty high tech

In a nutshell they are preheating the diesel before injection. They heat the diesel to 450 degrees Celsius under high pressure. They say they achieve it by utilizing the engines exhaust.

To me I think this would be difficult to achieve sustained high temps consistently. Some kind of electrically controlled flash boiler or transducer may be needed for system reliability. One would also have to be careful of starving the diesel engine. To me this would be like the ultimate way of leaning out the engine. We all know when you lean it out to much on a diesel it just dies on you! However by utilizing water/meth injection in conjunction may provide the needed fuel boost for steady reliable operation under load. Just up the meth to water ratio to improve combustion and prevent water lock.

I have heard of quite a few people trying to do this with gas cars as its much easier to vaporize gas fuel. However most people have mixed results as its supposedly hard to control and obtain the right air/fuel mixtures under the various driving conditions. To me the system would need to be variable in its operation to be effective. It would have to be able to adjust to the varying engine loads to be effective.

The other side similar to this supercritical fuel injection is fuel evaporation. Again used in gas tech and would not be applicable to diesels as they do not evaporate near as easily as gas.

Here is a link to one such unit I came across some time ago that seems to work reliably = 1st AGS Gasoline (Manufacturer of the Fuel Vaporizer MPG System) Carburetor Vaporizer Fuel Adapter

I think the term supercritical is simply a fancy term for vaporizing the fuel and is something that has been experimented with for along time. I think this is on the lines of the holy grail to supreme fuel economy. Supreme fuel economy would be in my opinion getting over 240mpg. It is encouraging that somebody is trying it with diesel because to this point there has been little attention given in this area of potential gain for diesel technology.

This research sets the stage for catalytic fuel cracking and is the holy grail of supreme fuel economy If a person was able to achieve this in an diesel or gas auto of average size they would be able to easily achieve 200+ mpg figures However we probably would not see them around to long LOL!

So some interesting concepts to think about as it pertains to increasing diesel engine efficiency.

GH..

The MIT and Transonic research is not just simple heating of the fuel for the sake of improved vaporization ( layman's terms ). Super Critical is a term used to describe the point in a standard phase diagram where the three states of matter come together. For diesel fuel, this is at several hundred degrees Centigrade and several thousand pounds per square inch pressure. But, one cannot just simply heat and pressurize the fuel to the critical point as time is a factor. At those elevated temperatures and pressures, carbon forms into solid deposits within Milli-seconds. Transonic has gotten around this by preheating the fuel to sub critical levels and then using an electrically heated injector pintle to add the last bit of heat at the very last moment.

This exercise is not just to get better vaporization. It changes the combustion profile of diesel.

In standard diesel injection, the fuel has a slight heat release delay as the shear caused by the fuel velocity forms small droplets that start to vaporize and form combustible mixtures which then can oxidize and start the flame. The heat released follows a curve and so does cylinder pressure as more fuel is fed into the flame front. Droplets do not quite completely evaporate and thus form carbon solids ( soot ) even with modern 30K psi injection systems. Yes, the high pressure common rail systems reduce soot, but they just produce smaller amounts of it in smaller sizes.

With super critical diesel injection, the high pressure plus the high entrained heat cause the fuel droplets to not just evaporate and start combustion. The fuel droplets do evaporate but combustion is delayed as the fuel has enough enthalpy ( energy ) to add to the hot air and the kinetic energy ( more enthalpy ) and endothermically produce dissociated combustion sub species. Some people call these sub species combustion precursors. But, in reality, they are part of combustion. They are the left overs after the long chain carbons (dodecane - a major component of diesel ) have been broken up. They include very reactive hydrazine and hydroxyl molecules as well as others. This reactive cloud penetrates deeply, mixing into the hot oxygen rich air absorbing energy until it spontaneously starts combustion in full. The flame front is large and broad in comparison to the narrow one found in standard combustion. Practically all the fuel is burned as droplets have additional time to evaporate and very little soot is formed. Also, due to the rapidity of final combustion, Nitrogen has not the time to form NO as it is much more "lazy" then the more reactive Carbon, thus reduced NO is a byproduct.

The combustion delay followed by a sharp heat release means less negative work (pressure rise before top dead center - TDC ) and more positive work ( pressure increase after TDC ). This results in more power produced for the same amount of fuel. Transonic is reporting greater than 50% thermal efficiency at partial power output. This compares favorably with the very large diesels found in ships and power production.


You mention catalytic cracking as a means to "super fuel efficiency". But, in essence, that IS what is taking place within a super critical injection system. Yes, we could save several tenths of unity of lost energy by performing the cracking outside the combustion chamber via recycled heat and catalyst chambers, but you would just push the 60% thermal efficiency level. Apply such an engine to my 4200 pound Dodge Hemi Magnum and I would go from 25 miles per gallon (mpg) to above 50 mpg. I would be VERY happy with this but it is NOT "super fuel efficiency". However, apply this engine to the Vetter style streamlined bikes or some of the slick constructs on this forum such as OLD MECHS streamlined tadpole and you may just get your super fuel efficient vehicle!

And on a side note, I was one of those college kids in the 70's who bought plans from the back of Popular Mechanics and built vapor carbs and so forth. I built GEET type reactors as well as HHO generators. I know how they work and how they don't. After several undergraduate degrees in science and engineering and beyond, I am still here. The government does not do away with people who have knowledge of new technology, they hire them! There is no great conspiracy.

[euromodder]

The main question : does it just about eliminate particulate emissions ?

If not : development is futile.

[RustyLugNut]

Originally Posted by euromodder

The main question : does it just about eliminate particulate emissions ?

If not : development is futile.

Are you speaking of the MIT/Transonic developments in super critical fluid injection? If so, yes. They drastically reduce particulate emissions.

[euromodder]

Originally Posted by RustyLugNut

Are you speaking of the MIT/Transonic developments in super critical fluid injection? If so, yes. They drastically reduce particulate emissions.

That's a good thing then.

Minuscule PM is the achilles' heel of Diesels, and we're only just getting to scratch the surface of long term PM health problems.

[GreenHornet]

An interesting tech that can be applied to gas and diesel Internal combustion engines. This simple modification to the ICE utilizes a unique yoke arm to substantially prolong piston dwell time and hence significantly increase engine efficiencies. This technologies focus is eliminating the piston friction and in turn creating an ICE that has superior fuel economy, power, and reduced emissions.

Website technology link = 100 MPG, Car Engine Efficiency, Fuel Economy, for Piston Engines

Gh

[ERTW]

Originally Posted by smokey442

Convert it to run as a homogenous charge compression ignition engine. No more need for turbocharger and near zero nitric oxide and hydrocarbon production when done correctly.

1. running stratified charge is how diesels manage to run ultra lean. This improves economy and soot emissions. running homogeneous mix would defeat this.

2. because of the high compression ratio, the valves need to be opened/closed so that they don't hit the piston. This increases pumping loss. So a turbo IS needed to overcome this. Removing the turbo will hurt economy AND power.

3. It's the high compression ratio and lean running that leads to NOx.

So your suggestion is to make a 40%+ efficiency diesel run like a 33% efficient gasoline engine?!

To make the *engine* more efficient, which is the original intent of the OP, you can reduce pumping losses further by porting, back cut on the valves, and a good valve job. Late intake valve closing will further reduce pumping losses, as well as kill a little power i.e. a bigger intake cam. Kind of a Miller cycle diesel

[GreenHornet]

I have been doing a lot of research into diesel technology and future developments. From what I can see the potential future looks bright. Looking back into history the only problem I see is the time to bring to market. Many of these great ideas unfortunately I will never see in the mainstream more than likely in my lifetime. This is very unfortunate as these are brilliant engine designs that have an immediate need now and not a hundred years from now!

A few engine designs that I did not cover in previous posts that I think are very relevant to this thread are the (OPRE) Opposed Piston Pulling Rod Engine, (PatOP) Single Crankshaft Opposed piston Engine, and (PatPOC) Single Crankshaft Opposed piston Engine of different design. These engines can be considered offspring of the Junkers Doxford engine. These are opposed piston engines that are direct injected with diesel. With some modification they can also be spark ignited gas guzzlers! These engines spend more time at BDC and increase piston dwell to increase engine efficiency among other improvements. They have far less parts as well as far less moving parts then a conventional diesel today. They are far lighter and much more compact in design. They can literally fit under the seat of your car how is that for packaging.

In my humble opinion this is where I see the future of the diesel engine for its simplicity and efficiency advantages.

Here is the website where you can find very detailed explanations of how the engines work there advantages as well as comparisons. There are also lots of animations and videos of the prototypes for viewing. A very well done site with tons to share and learn from. My hats off to Mr. Pattakon for developing these engines and sharing them with us through his website

Website Link = http://www.pattakon.com/pattakonOPRE.htm

GH..

[GreenHornet]

Originally Posted by ERTW

1. running stratified charge is how diesels manage to run ultra lean. This improves economy and soot emissions. running homogeneous mix would defeat this.

2. because of the high compression ratio, the valves need to be opened/closed so that they don't hit the piston. This increases pumping loss. So a turbo IS needed to overcome this. Removing the turbo will hurt economy AND power.

3. It's the high compression ratio and lean running that leads to NOx.

So your suggestion is to make a 40%+ efficiency diesel run like a 33% efficient gasoline engine?!

To make the *engine* more efficient, which is the original intent of the OP, you can reduce pumping losses further by porting, back cut on the valves, and a good valve job. Late intake valve closing will further reduce pumping losses, as well as kill a little power i.e. a bigger intake cam. Kind of a Miller cycle diesel

ERTW good points on the last paragraph there. I will have to look into the Miller cycle a bit further.