Diesels get cleaner when they raise their efficiency. That's how you get clean running diesel cars that get 45 MPG.

Only if the original design was a really bad and inefficient one given the better designed cars 40+ years ago were doing that fuel milage with all mechanical injection on far larger and less aerodynamic vehicles..

To be honest most modern electronically controlled emissions compliant ones can pick up a good deal more efficiency by dirtying them up a bit and its not really much of a secret.

I for one have worked side by side with they guys who work on big truck and industrial and farming engines and I have seen first hand how a bit of detuning of the emissions made some surprising improvements on engine power and fuel burn rates.

Its similar to how a plastics manufacture will tell you how great their products are but its the reality of those who have to work with it every day can tell you whether its as good as the say it is.

 

Most modern electronically controlled engines, in fact probably all, burn cleaner and more efficient than their older counterparts. At least in passenger cars and trucks, don't know about tractors and such. For example, the Duramax diesel is cleaner and makes much more torque and power and better effiency than the introductory models of 15 years ago. You'll find similar numbers when you look at other manufacture's offerings.

And the newer 45 MPG diesel cars make 3 times the power as their smoky old cousins of 40 years ago, with much cleaner emissions.

 

Most modern electronically controlled engines, in fact probably all, burn cleaner and more efficient than their older counterparts. .

Modern Diesel engines run cleaner... but not more efficient... But I need to go find hard data to sustain my point before arguing any further... I'll be back with the confirmation (or rebuttal... I can always be wrong, of course) of what I've just said...

 

Modern Diesel engines run cleaner... but not more efficient... .

You gotta be kidding. They not only run more efficient, it's a no-contest. Gone is the black spot near the tailpipe. Gone is the stench and smell of unburned fuel. Modern electronic engine controls, valve timing, improved injection technology, improved turbo/intercoolers all add up to a cleaner, more efficient and better performing engine. It wouldn't make any sense to say they are cleaner and less effecient.

 

From the Wikipedia:

Advancing the start of injection (injecting before the piston reaches to its SOI-TDC) results in higher in-cylinder pressure and temperature, and higher efficiency, but also results in increased engine noise due to faster cylinder pressure rise and increased oxides of nitrogen (NOx) formation due to higher combustion temperatures. Delaying start of injection causes incomplete combustion, reduced fuel efficiency and an increase in exhaust smoke, containing a considerable amount of particulate matter and unburned hydrocarbons.

That's my point. I know as a matter of fact that, for instance, the most recent models of Cummings SX15 engine run cleaner, but have about 5% less efficiency compared with those of ten years ago. They've sacrificed efficiency to make them comply with modern emission standards.

 

You gotta be kidding. They not only run more efficient, it's a no-contest. Gone is the black spot near the tailpipe. Gone is the stench and smell of unburned fuel. Modern electronic engine controls, valve timing, improved injection technology, improved turbo/intercoolers all add up to a cleaner, more efficient and better performing engine. It wouldn't make any sense to say they are cleaner and less effecient.

Maybe you're talking about much older engines? say 30 to 40 years old?

 

That's my point. I know as a matter of fact that, for instance, the most recent models of Cummings SX15 engine run cleaner, but have about 5% less efficiency compared with those of ten years ago. They've sacrificed efficiency to make them comply with modern emission standards.

Yep thats about the same basic numbers the guys I worked around had. Some were even better. The newer John Deere diesels they have in the big tractors and combines can be retuned to easily put out 10 - 15% more HP and while burning 10 - 15% less fuel doing the same job.

The one family of farmers I used to haul sugar beets for in the fall had one of their new JD combines reprogramed just so if it would make much difference. Well they said it took all of two days in head to head field work with its two identical twins to show that shutting down the emissions crap and related tuning easily added more power plus it was burning at least 10% less fuel per day doing the exact same work in the exact same fields.

They also had one of their Kenworth semis reprogrammed as well and that one had way more power than its identical partners plus also used less fuel as well yet could roll a black cloud like no other when the drivers got on it.

Now as the new diesel pickups go I have worked with enough guys who have had reprograms done on them to know for a fact that they too get way better power and fuel milage with the emissions systems shutdown and the fuel maps redone to favor power and efficiency Vs emissions and that includes the new duramax's as well.

Industrial applications wise I have also seen enough of the new emissions compliant engines retuned to get way better fuel consumption and power rates than they ever did when they were set for best emissions numbers.

BTW most of the newer drive by wire diesel engines have the ability to have their on demand instantaneous power output and fuel consumptions rates displayed when connected to a laptop with the right programs so its very easy to compare their before and after numbers.
I know that when I worked at the oil field last year as one of the electronics techs I had software that would let me look at the big 2500 HP diesel engines running numbers and it was easy to see the differences between one of the re tuned pumps and a stock set one. The stock ones would be at 100% power and burning around 100 - 104 GPH while the tweaked one right next to it doing identical work would be running at 90 - 94% load while burning 88 - 92 GPH.

So yea from my perspective if anyone tells me the new diesels are cleaner and more fuel efficient I say BS. Pretty much any diesel that is set up to meet American emissions standards is far from being the most efficient it can be.

 

From the Wikipedia:

Advancing the start of injection (injecting before the piston reaches to its SOI-TDC) results in higher in-cylinder pressure and temperature, and higher efficiency, but also results in increased engine noise due to faster cylinder pressure rise and increased oxides of nitrogen (NOx) formation due to higher combustion temperatures. Delaying start of injection causes incomplete combustion, reduced fuel efficiency and an increase in exhaust smoke, containing a considerable amount of particulate matter and unburned hydrocarbons.

That's my point. I know as a matter of fact that, for instance, the most recent models of Cummings SX15 engine run cleaner, but have about 5% less efficiency compared with those of ten years ago. They've sacrificed efficiency to make them comply with modern emission standards.

Wiki didn't tell you what the effect on other pollutants are, CO, SPM's, N2O and HC's. Often, tuning for one just trades it for another. So I wouldn't say the exhaust is "cleaner" unless I know how the tuning affects the other emissions.

Looking at the 6.7L Cummins design's strategy for reducing Nox, it appears they employs other strategies, as EGR control, Diesel Oxidation Catalyst, Absobtion Catalyst, and Selective Catalyst Reduction. No mention of retarding the timing though.

 

Wiki didn't tell you what the effect on other pollutants are, CO, SPM's and HC's. Often, tuning for one just trades it for another. So I wouldn't say the exhaust is "cleaner" unless I know how the tuning affects the other emissions.

Looking at the 6.7L Cummins design's strategy for reducing Nox, it appears GM employs other strategies, as EGR control, Diesel Oxidation Catalyst, Absobtion Catalyst, and Selective Catalyst Reduction. No mention of retarding the timing though.

Now we're on the same page... I've got plenty of data regarding the Cummings engine. Thing is I'd have to dig deeply for it to get that particular piece of info. But I've been working in the transportation industry for a few years, and all of the owners I know make the same complaint: that the new trucks engine's have decreased their efficiency in order to reduce Nox emissions.

 

Agh! You caught my typo before I was able to fix it! Of course, I didn't mean GM, I was reviewing the Duramax at the same time.

 

I used to work in the elevator biz and I collected a box of polyurethane rollers and left them in storage for about 10 years.

However, they have decayed into something like wax and they crumble from just handling them. Polyurethane does have a limited shelf life and severe decay is a normal process.

 

Diesels get cleaner when they raise their efficiency. That's how you get clean running diesel cars that get 45 MPG.

Make perfect sense to me -- soot and CO emissions are naught but wasted fuel

 

Make perfect sense to me -- soot and CO emissions are naught but wasted fuel

HP, the issue is a little more complicated than that. Diesel emissions are classified in several types, like soot, CO and NOx for instance. At a certain point, there's a trade off. When you try to diminish one, the other emissions tend to increase.

 

I think the two camps are talking about different versions of efficiency. Removing catalytic converters and retuning (based on less back pressure, etc) will yield more power from the engine. Now, is that more efficient? It depends how you measure efficiency. Power/mass? Maybe. work done/day? Maybe.

Most engineers measure efficiency as work done / fuel input.

Modern Diesel engines suppress combustion until later in the compression stroke and, therefore, leave more un-burned fuel in the exhaust which has to be consumed in the catalytic converter as waste heat.

Older Diesel engines started combustion earlier in the compression stroke and, therefore, started to rumble at low rpms (if the engine decelerated too much before each combustion event). Even with a fly-wheel, the rotation speed of an engine is not uniform at each degree of rotation - Honda actually uses this to determine which cylinder is mis-firing in their engine monitoring system - "check engine light"). In any case, the earlier detonation also required heavier (stronger) engine blocks which cause efficiency losses.

Today, there is a sort of balance of motivations and rewards in Diesel engines. The higher-revving gives them less of a tractor-pulling-a-tree-stump feel and more of a gasoline engine feel. Less soot and smell, less gas milage (because they are generating more horse power and, therefore, achieving higher acceleration rates off the stop light) than old Diesel engines.

It is all a compromise. In the end, the cost per mile driven is about the same today because diesel fuel is no longer cheap (in the US). To get high milage with reasonable acceleration, a turbocharger and pressurized fuel rails are needed. Too much complexity and high repair costs for my expectation of a vehicle (12 - 15 year lifetime with 150k miles). Maybe this happens in pickup trucks, but that is not my domain.

I leave Diesel engines to heavy haul trucks.

 

HP, the issue is a little more complicated than that. Diesel emissions are classified in several types, like soot, CO and NOx for instance. At a certain point, there's a trade off. When you try to diminish one, the other emissions tend to increase.

I tend more toward economy than ecology --- So I say wring the 'bottom calorie' out of that fuel and 'fix' that nitrogen for the benefit of the agrarians! -- On a somber note, however, I regard the H2S and SO2 emissions troubling for the damage afforded 'marble' sculpture

Best regards
HP

 

... I leave Diesel engines to heavy haul trucks.

That, I think, is where Diesel engines' core market is. Their robustness and reliability are superior to gasoline engines.

 

Whether retarded timing or other means are used to control emissions, fact is the diesel engine has evolved into a much cleaner and efficient machine. Modern diesels are lean burning, so less HC's and other nasties, while achieving better fuel economy. Remember the trails of black smoke of yore? That was a signal of inefficiency. Modern diesels don't have that.

My first diesel was a 6.9L Ford IDI. It produced a whopping 175 horsepower and got about 11 MPG. The 7.3L Power Stroke with electronic engine management made 250+ HP and got 16+ MPG on vehicles with the same weight and gearing. More recently, diesel engines are pushing 400HP with minimum impact on fuel stinginess, and with much cleaner exhaust products. And, as pointed out, smaller passenger cars are cleaner, more powerful and more efficient than before.

Engine developers aren't just using methods that trade one emission product for another. That is done, but that's not the whole story. Modern engines are lean burn and use a variety of catalyst technologies to remove or convert some of the more harmful products. Could they be more efficient? Sure, but that doesn't contradict the progress made over the years.

 

Modern diesels are lean burning,

All diesels are lean burning. Find me one that runs on compression ignition cycle that isn't.

 

Advanced lean burn technology provides for more complete combustion under varying loads by more precisely controlling the amount of fuel injected, through advanced combustion geometries which better atomize fuel and by other means.

 

So that's technical speak for no then?