Diesel Engine Inefficiencies

Are you looking for a sabotage line of tricks? Start with "no fuel"?

The laws of physics.

Law of physics is not a cause of inefficiency it is a tool that allows improving efficiency by finding needed design change.

Everything he/she says

The mention of ignition advance, for a diesel, would make everything he/she and you say, lack even the tiniest bit of credibility.

Here! Here!...........and notice it is one of the illegal boat people (we have a problem with this in Australia)............no identification, e.g. name, country of origin, etc....they destroy their papers.......and their brains.

I think diesels are very well made considering the pressures they endure, but one of the forgotten inefficencies is the cost to produce a engine, mining, smelting, machining, and production, before a drop of fuel is added, diesel truck engines are noted for 50,000 hours or more before overhaul and I know of one large party boat that made a 100,000 hours on a cummins 6 turbo before replacing it with a john deere clean burning engine under gov tax break, diesels inject fuel to start the combustion a few degrees before top dead center but the actual pressure rise does not start until after tdc, most of the exh heat and friction from accesories and pumpung coolant and oil have been studied for decades to see if they could be minimized, one of the reasons electric and clutchable cooling fans are now a design must, peugeot used electric clutches on cooling fans since fifties..

Sincerely

Mitch ret peugeot mech
P:S: I think I may register with this site as I enjoy reading 30-60 percent of it.. Go Giants...

I also believe diesels are very well made, and very efficient in real world conditions. I drive a 2000 Jetta TDI (turbodiesel) that averages better than 50mpg. The only modifications i have done are removing flow restrictions up to the air filter, putting two deep cycle batteries in the trunk (mainly charged off solar and a 1.5 amp trickle charger, but i do resort to a more rapid charger if i know i am taking long trips back to back). Other than that, i don't pretent i'm part of the NHRA, i run my tires at 90% of the max sidewall pressure, and only fill up with diesel with a cetane >=40. 57 mpg was the best i have done and i have never been below 50 mpg since eliminating the alternator (>20% improvement in mpg). I'd say that a 10 year old diesel getting better mileage than brand new gasoline hybrids suggests diesel are very efficient in the real world. Bbb flee to me remote elf

I just love experts of XIX century technology like diesel engine. They do not imagine anything else but the thing read in papers. Since when a device less than 80% efficient is considered well design? Friction is the least important cause of energy loss in diesel engine. More energy is disposed due to advancement of ignition. Also consider that diesel if not cooled would melt. Why? can you answer this?

Pressure indurence has nothing to do with quality of design, as the purpose of design of every engine is to convert one form of energy into other i.e. diesel converts energy of heat released from fuel into torque and rotation that is mechanical power. Here the rub is! Releases of energy from fuel is slow in diesel engine and power is defined as the energy release in time, thus power of diesel is not as high as it should, if diesel could withstand detonations of fuel. Do you know why diesel cannot withstand detonations?

What a pointless monologue......why did you bother yourself with posting?

Did you type your diatribe out on your cellphone from a keg party perhaps between rounds of beer pong? Your post reminds me of the boasts of someone who has recently consumed far too much cheap liquor is a very short time, yet it hasn't yet knocked their dic in the dirt, so the blather on believing they are impressing everyone with condescending authoratative claims. You were drunk, right? …'ignition advancement…' in a diesel, please expound... .. ... . When you were making up your claims about diesel not handeling detonation, how many people did you expect would believe you. Bbb … Better to keep your mouth shut and risk suspicion you are a fool, than to take your path, removing all doubt.

Would be less confusing if one of you registered - as it looks a bit 'bipolar' and like "Fight Club" without either character actually knowing "how to make soap".

True.

Re: There are many causes of inefficiency handed down from generation to generation, but most important is incomplete expansion of exhausts because exhausts when expanding produce work and cool at the same time.

I wonder how much of that waste heat could be "recovered" by some means--maybe a Stirling engine either helping to drive the mechanical load "directly", or in something like a hybrid vehicle, driving another generator (to charge batteries or drive electric motors).

Does anybody (here) have any kind of feel for how much power you might recover that way? (I guess I've also read about people trying to use a Peltier junction approach (iiuc) to convert waste heat to power...)

.........incomplete expansion of exhausts because exhausts when expanding produce work and cool at the same time.

A turbocharged diesel engine can improve engine efficiency (SFC) and increase power output by up to 35% with efficient charge air cooling..........particularly in marine engines where the charge air cooler (inter-cooler or after-cooler) is cooled by sea water.............also in marine applications waste heat from diesel engine exhaust is used either as an economiser for boiler feed water or directly as a waste heat boiler.

Don't forget the amount of heat that goes to the cooling systems........this heat also can be put to good use in marine applications.

clogged filters,bad rings,bad injector or injector pump,crap in the fuel. pilot error.

You have forgotten about gun-engine that is 445.6% more efficient than best diesel.

Go Google and type "gun-engine"

Wow - "445.6% more efficient than best diesel"

So is that twice or 11 times the fuels maximum theoretical energy?

Oh never mind the math - I'll take two!

guest wrote: 'Go Google and type "gun-engine"'

Ok, I did that, and I found some interesting potential engines--but one seems to have been under development in 2003 and one in 2008 (at least that's the date of articles I could find on them)--where are those engines now?

• "Stan" Holubowicz's gun engine on a wiki page where the latest developments seem to go up to some date in 2008: http://peswiki.com/index.php/Directory:Gun_Engine#Official_Website
• A 2003 PopSci article on a pulse detonation engine--iisa (if I skimmed accurately) some big companies (GE, Pratt & Whitney, ...) got involved with the technology, but where is it now?: http://www.popsci.com/military-aviation-space/article/2003-08/after-combustion-detonation?page=2
• I also found information on similar engines arranged in a linear configuration to generate electricity (directly) instead of mechanical force / torque--there are various engines here, and I'm not sure of any dates, but the latest date on this page was in 200809 (unless I missed something)--start at http://peswiki.com/index.php/Directory:Linear_Combustion_Electromagnetic_Engines (btw, this seems like an interesting idea (that is, magnets in the piston to move past coils and generate electricity directly)
  

So where are these technologies now?

Dead right and where are the videos showing a working example????

Where are the drawings (hopefully animated as well) showing how it works in principle...

Till I see such stuff, it comes over as a big con.....even then it still may be a con, but slightly less likely.....

Under-loading and atmospheric pressure are two that come to mind.

Needing an oil change or a fuel filter change.

Excellently put.

",a petrol engine is more efficient...... ......in practice, a diesel engine is more efficient...' . . Yeah, well, in theory bumblebees aren't supposed to be able to fly. In practice, they do quite well. .. .. .. Two big problems with petrol engines .. .. 1. unless under wide open throttle, pumping losses are significant because speed is controlled by forcing the engine to pull air through a restictive butterfly valve. Imagine making a horse breath through a straw every time you wanted to slow a carraige down. .. .. 2. With few exceptions, petrol engines require a rich fuel/air mix, always adding more fuel than the air can burn, mainly because the are too weak to handle anything other than a smooth burn. Diesel engines are lean burn engines where detonation isn't a catastrophe, but standard ops .. . . . Bbb . . . Flee to me remote elf

I should have added that the efficiency of an engine is largely dictated by compression ratio, higher being more efficient, but the gains drop off at about 14:1.

Diesel engines generally have much higher compression ratios, although modern petrol engines are getting higher. High compression ratios mean the space in the cylinder head for the heads of the valves is limited. It also means that the engine has to be built more robustly to tolerate the pressures, hence diesel engines generally being heavy. The diesel combustion process is noisier too, so the use of cast iron for the block tends to damp the noise better.

If we are talking thermal efficiency or torque or fuel efficiency...........the diesel is in front..........one of the reasons why the sale of diesel powered vehicles is leading petrol vehicle engines. Even the large two stroke marine diesel engines (10 to14 cylinders-in line) have a thermal efficiency approaching 55%.

on a 4 stroke gas engine that has a higher than normal compression ratio the tops of the pistons have valve reliefs in them. I run a sbc 383 with 11 to 1 comp ratio with 64cc combustion chamber.I have no problems with clearance.Their are people that run 13 to 14 comp ratio in a gas engine and they don't have a problem with the piston hitting the valves.They also have to run higher octane gas @ 8 bucks a gallon us.It all depends on how you build a motor.I am totally a gas engine guy,but I do think it is amazing the economy and trq you can get from a diesel.A 1 ton dodge pickup with a diesel has enough power to pull locomotive and still gets great economy when set up properly.The one bad thing about a diesel is if you over rev it its a goner,sames a gas but at a much lower rpm.Also diesels can be a real pita when it gets cold. On a cold morning at a construction company that I worked @ when the drivers would start the diesel trucks their would be enough unburned fuel in the air to burn your eyes. And I don't like dodges either. .02

93 octane costs an average of $3.25/gal around here. Unless you are running 100 octane AvGas (with tetraethyl lead), $8/gal sounds wrong.

Why does 8 bucks sound high.Call your local drag strip and see what they sell it for I can buy 93 octane for 2.89 to 2.94. cam 2,(bought out by another company) 100 and 110 no lead, I can get every day for 8 dollars a gallon. Not many people run av-gas, at around sea level anyway,it has a different flash point. Why do you think in a small aircraft the pilot adjust the mixture and timing prior to take off.Thats if you want to stay alive.

sorry for getting away from the original topic

93 octane costs an average of $3.25/gal around here. Unless you are running 100 octane AvGas (with tetraethyl lead), $8/gal sounds wrong.

Sorry for getting away from the original topic

like I said, unless they are running 100 octane AVgas....

And yeah, I was a little high on the 93 octane price. I priced it on the way to work this morning (I don't normally use the stuff) and 2.90 seemed to be about the price point.

Well said. I was wondering when someone would mention a two-stroke diesel engine.

Major oil companies charging 300% profit on a gallon of diesel fuel.

Thermodynamics. It isn't just a good idea, it is the LAW.

I've always wondered why the top of a piston couldn't be coated with ceramic cap so that the combustion heat could be raised and centralized to counteract the cooling effect of the incoming atomized fuel.

Because the compression stroke and the firing stroke are usually the same length, the exhaust energy cannot be fully utilised.

Somewhere I read about engines that have different length compression to exhaust strokes that manage to utilise the fuel more efficiently.

In fact I think there is a CR4 member who participated in designing such engines......hopefully he will chime in an give us more details.....

Also there are dual piston (in one bored cylinder) engines with no heads that also manage to do just that.....

But generally speaking, diesels are in the real world more efficient than other IC engines, even without fancy attachments and features!!

'Somewhere I read about engines that have different length compression to expansion strokes' .. .. .. .. .. .. .. . . . . . ., , , . .. it is much easier to change the effective stroke by closing the intake valves after the pistol has traveled some initial portion of what will be the compression stroke... rather than differing the actual Stroke length. I believe toyota does this in the prius. .... ... ..... ..... . ... ... .. Bbb . . Flee to me remote elf

The cycle you are thinking of is probably the Atkinson cycle, where the compression stroke can be different from the expansion stroke.

Effectively this is what a turbo-charger does, by expanding the gases further than the piston can. In fact it is possible to have positive pressure on the induction stroke.

The talk of 55% thermal efficiency in the big two-stroke diesel engines is an interesting point. These figures are right, but if you look at the theoretical compression ratio of the engines and the efficiency, the laws of thermodynamics predict a lower efficiency. This is because extra compression and expansion occurs in the turbo-charger. These are a compound machine. This is one law (well there are more than one ☺ ) that you can't break.

Typically 2 stroke engines are less efficient than 4 stroke because of the loss of piston travel. There are 3 fazes to a 2 stroke -compression - power - but we tend to forget the scavenging faze that is about a quarter of its rotation the loss of power stroke can be herd as the unburnt fuel blasts into the exhaust manifold, we have gotten away from them for more than just there noise. We piqued are efficiency at about the year 2000 to 2004 era but they clamped down on emissions and many of the emissions control systems are really hard on fuel. Cat and others used a afterburner to clean out a restrictive catalytic converter. I never understood the logic to some of these.The fuel itself has an emission cost long before it gets to the fuel tank why would you want to burn more?And at what point do we loose any gain we were looking for? I have run older and bran spankin new in short haul trucking and found an increase in consumption of about 20%. My 2004 3/4 ton 4x4 gets 25-26 MPG my friend has the same model 2010 and cant get 20 MPG we have roughly the same driving habits. I'll leave the rest to you

?-can any one say that thar 3/4 ton 4x4 4door pickup gets 16 MPG pulling a 30 foot holiday trailer on gas

True, they are less efficient than a 4 stroke, but since they have twice as many power strokes per revolution, you can get more power in a smaller and lighter package which makes them very desirable for skid mounted power units which must be portable, and in the oil biz case may have to be airlifted by helicopter into otherwise inaccessible places or placed on offshore platforms which are often weight restricted structures. 2 stroke Detroit Diesels still rule the roost in the oil business because of their high power to weight ratio. Companies will spend an ungodly amount of money to refurb/rebuild an older (and therefore exempt) 2 stroke Detroit (which is allowed under EPA rules) instead of buying a new four stroke Detroit or Cat or MAN for that very reason.

The question made by guest is so general,not clear to me what exactly he is asking but answers (some of them,at least) deserves answers too:The efficiency of any engine is determined by its cycle,good to know today the so called "diesel engines" don't follow the diesel cycle:1)The old diesel engines ("blowers") which follows that cycle, keeps the same pressure along first part of expansion and work than at end of compression.This don't happen in modern "diesel" engines:Ending compression pressure skips and gets 1.75 (close that) times the value it had in a so short while at rates of 11.5 (too soft) to 24 (too hard running) kbar/sec,this is the mixed cycle (volume constant-pressure constant). 2)Other interesting question is the cycle by itself don't mean more efficiency: If an engine follows an Otto cycle with a compression ratio of a diesel engine will be much more efficient than the diesel one :Technical reasons like materials resistance prevent this.The theory says the mixed cycle could reach not much more than a 50% of use of energy in fuel and the most efficient engine (biggest too) is very close that in some regime.Old info from old gasoline engines theory i have (compression ratios of just 8 against 9.5 to 10.5 in moderns) tells about a possible and hard to reach 45%.So these questions are studied several decades ago and are so complex:Theory must be studied deeply and carefully.-

I'm surprised that no one's mentioned energy density, especially with the comparison of diesel vs. gasoline engines. From the figures I've found on the web, diesel has about 10-20% more energy per gallon than gasoline, making it a more efficient energy transfer medium to start.

Good catch! I sort of thought it had been hinted at, but I went back through the comments and don't see it mentioned--I guess I did see the ones that, in general terms, said a diesel was more efficient than a gas engine, but nothing about the energy content of the fuel.

Energy density has no direct effect on efficiency. Efficiency is the shaft power delivered divided by input power in the fuel, irrespective of the quantity of fuel.

Also, as you say, diesel has more energy than gasoline per gallon, but this is because the SG of diesel is higher. On a mass basis, energy content is about the same.

Cheers.......Codey

True, but the typical (especially in automotive) measure of engine fuel efficiency is in miles per gallon. I had noticed that in some explanations of energy density they measure it in joules per unit mass.

As for energy density and efficiency, gasoline and diesel are apples and oranges. There is more energy available to deliver to the shaft with a gallon of diesel than a gallon of gasoline. Comparing the two combustion systems and power delivery methods can only go so far. It's a far better feat to get 50 mpg out of gasoline than the same out of diesel.

OK Lo Volt, fair comment, drivers think in terms of miles per gal rather than % efficiency. I must admit I've never thought of adjusting for fuel SG when comparing gas and diesel mpg.

Even more relevant is miles per $ or £. In UK diesel is a few % dearer than unleaded (more tax). Used to be cheaper some years ago as I believe cheaper to produce, maybe different now demand balance has changed in favour of diesel. How do they compare in USA?

Codey

Codemaster wrote: "Even more relevant is miles per $ or £. In UK diesel is a few % dearer than unleaded (more tax). Used to be cheaper some years ago as I believe cheaper to produce, maybe different now demand balance has changed in favour of diesel. How do they compare in USA?"

Pretty much the same story, I'm guessing that five or so years ago, diesel was cheaper than gas, now gas is cheaper. Without actually paying attention to diesel prices, it seems to be in the range of $0.20 to $0.30 more than gas (with current gas prices around $2.75 per gallon (in my part of the US).)

I'll concur, about $0.20 to $0.30 higher than gasoline.

I'm told that in Europe there are more cars running diesel than gasoline not counting trucks and heavy equipment. This higher demand for diesel may account for the higher price. Here in the US, diesel running cars still don't account for more than a small percentage. Although in the last few years diesel pickup trucks have become more popular.

Soot ........ since you are a guest, I presupposed you didn't want to discuss Otto and the Carnot cycle, relating to thermodynamics. does that help answer your question?