Why no two-stroke diesel cars? 4

[kj16v]

Hi all. I joined purely to ask this question:

I've just been reading about two-stroke diesel engines. How come there aren't any cars or road vehicles with this type of engine?

Also, there are plenty of cars with turbo-diesel engines. Why aren't there any cars with supercharged diesels?

Cheers

 

[TheBlacksmith]

Two stroke diesels generally do not meet emissions standards which is why they're being phased out in favor of four strokes.

Turbocharging is supercharging. So is closing the exhaust prior to the intake on a two stroke diesel with a pressurized air box.

 

[swall]

Detroit Diesels, of course, were two-stroke, supercharged with a Roots blower. But, I don't think any ever made it into light truck use, let alone pass cars.

 

[kj16v]

Blacksmith: So Two-strokes are being phased out on ships, etc? What makes the them have poor emmissions?

"Turbocharging is supercharging. So is closing the exhaust prior to the intake on a two stroke diesel with a pressurized air box."

Sorry, I didn't quite understand your reply there. I know turbocharging is a type of supercharging, but I meant why don't diesel passenger cars use crank driven Roots or Whipple (screw) type blowers? Surely their ability to provide boost at low rpm would make them perfect for low revving diesel?

Swall: What were the "Detroit diesels" used for?

Thanks for the answers so far. Keep 'em coming, people!

 

[dgallup]

Ships don't have any emissions requirements.

Mechanically driven superchargers are less efficient than turbo superchargers.

 

[catserveng]

Beg to differ, ships do have emissions standards, International Maritime Organization has imposed standards, and while currently not as strict as other markets, are having an impact. Also local air districts in many countries are imposing regulations that restrict using heavy fuel (HFO) on the mains within so many miles of port and for the ships service generators. Emissions regulations are impacting all internal combustions engines, every year more applications and smaller and larger size engines are being affected.

Detroit Diesel was a brand that evolved from General Motors and Gray Marine. The 71 series two stroke engine was developed in the 30's but didn't see much use until WWII. Main use was engines for small marine craft, such as landing craft, tenders, harbor work boats, etc. Towards end of war also saw use as generators and pumps. It was a very durable and reliable engine for it's power density in it's day. It was used in marine, power generation, on hiway and off hiway applications. The original versions were the 6 and 4 cylinder 71 series, 71 cu/in per cylinder displacement. The 53 series came out in the late 50's, and was in service until the 80's in lots of applications. The product line evolved into two larger families, the 92 series, primarily used in on-hiway trucking but saw use in marine and power applications and the 149 series. The 149 series was originally targeted for the oil and gas industries, mainly well servicing, but had a fairly good run for a short time in the standby power market.

As power density, fuel consumption and emissions improved on the four stroke engines, the two stroke just couldn't keep up in most applications. High pressure direct injection fuel systems and better turbocharging proably the best mechanical contributors.

I thought there were some European light duty vehicles with a combination of small supercharger and small turbo, maybe someone here in the forum has more info. I rented a Jeep Liberty in Denmark about 4 years ago with a small diesel power plant. If I could have bought one in the US when I got back I would have. I only glanced under the hood, but it was a nice package and it looked like it had a belt driven supercharger, maybe not. But it ran great, used little fuel and was responsive. I've heard Audi, Saab, Mercedes and Volvo have made great improvements in automotive diesels, too bad we don't get to see them here in the USA.

Mike L.

 

[patprimmer]

Turbos are cheaper and lighter and more efficient than belt driven.

As diesels run full throttle, lag is less of an issue.

As diesels tend to inherently have or to be designed for more low speed torque, lag is less of a problem.

Even without lag, the heavy reciprocating and rotating parts in a diesel causes a slower rate of response than a similar powered SI engine.

While diesels might be economical on fuel, they are expensive to manufacture, they are more difficult to get through emissions, they have less performance from low speed acceleration in lower gears relative to their power level, they tend to be noisy and they are heavy. Also in recent times diesel fuel prices have increased more than petrol so the while the MPG or litres per 100 Km is better the higher price has eroded that advantage.


Regards
Pat
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[rmw]

The 6-71 was commonly used as an over the road truck engine in the early to mid '70's in the USA. It was referred to as the 235 (based on HP rating). The 8V-71 was very commonly found both in trucks and buses until the 8V-92 came out and then no one wanted a 71. In trucks that was before advent the days of the big bore high HP diesels. For buses, they continued to be the engine of choice right up to the end of the last century.

Lots of 4-53's were retrofitted into pick up trucks by hobbyists, but it wasn't really widespread. It made a nice PU truck engine. If you had one, you could command a good price for it. They would snap them up. They were a popular replacement a lot of the early 5.7 and 6.2 GM and Ford 6.9 DI diesels.

Speaking of Detroit's, they blubbered oil terribly and they burned oil voraciously. An early '90's vintage 8V-92 O&M manual I have states that the rated oil consumption for a 10 hour operating period (about 500 miles travel in an automotive version) is 1 gallon. I think that was what it burnt, and didn't count what it leaked. And, believe you me, it was right. A tank of fuel was a guaranteed gallon of oil added.

Once I heard a trucker in the late '70's say to his buddy on the CB radio "you know, this truck of mine was prophesied about in the Bible." His buddy - "what do you mean by that?" Reply, "Well, the Bible says that in the latter days there would be crawling and screaming creatures upon the face of the Earth, and it had to be referring to this Jimmy Diesel of mine."

When Detroit Diesel determined to come out with a new engine in the mid to late '80's, they started with a clean sheet of paper and designed up a 4 stroke, and a good one at that as history tells us.

Based on the above, you probably couldn't give away a 2-stroke diesel to anyone in the heavy duty transportation industry in the USA, either based on their operating record or the current emissions regulations.

rmw

 

[Satanicusmaximus]

Why did Detroit diesels consume so much oil?

 

[catserveng]

I think the main reason is the piston rings carrying it up past the inlet ports on the liner, and the fact that the blowers seals all seemed to leak no matter what you did.

I rebuilt lots of blowers in my early mechanic days, using stock parts and procedures, the guys building them for race cars modified the seal bores and used different seals, but any of my customers trying to us "race modified" blowers had early hour failures.

By original design these were not a particularly "tight" engine. I think they leaked as much as they burned, and that was on a "good" engine. Rebuilding a high time engine meant getting REALLY dirty, air boxes were always packed with crud.

In their day they were tough, lots lived second and third lives (a lot used to be available on the military surplus market). They burned lots of fuel and oil and sometimes ran away.

And it seems the old detroits were bad, get around an old Cleveland 268 engine or an older Fairbanks OP, talk about burning and leaking! These were larger bore slower speed 2 stroke engines used in marine, small locomotive and some EPG markets. But tough old dogs.

 

[rmw]

I never thought of Detroits as a "bad" engine. I considered them to be very reliable engines. In heavy duty diesels, I have only ever owned Detroits and Cummins (4 stroke). I spent tons more money rebuilding and/or replacing Cummins than I ever did a Detroit. In fact I never did much to the Detroits other than steam clean them, change injectors occasionally and run the rack occasionally. CatServ has it right. You never knew where the oil in the airbox came from, from piston ring slobber or from blower seals, but the drains always blubbered twin puddles of oil when the vehicle stopped. And when you started it, the accumulated oil would clean out the mosquitos for blocks until it got up to speed.

Someone got the bright idea to pipe the air box drains back into the sump and promptly suffered an engine failure. There was just too much fine dust that got past the filters in that oil. Detroit had stern warnings in their O&M manuals against this practice.

But start... if they turned more than a quarter rev and weren't running, they weren't going to start. You could grind and grind on a Cummins and maybe it would start if you didn't run out of battery. If you had to grind on a Detroit, you were just abusing starters and batteries. If one of mine ever turned over more than about 4 times with out starting, I let go of the key and started troubleshooting.

They were very predictable. The 8V-71 wouldn't produce squat under 1800 rpm. But once there it would do its job. The way mine was geared, that meant taking it all the way out to 2100 rpm (I had the governor juiced to ~2200 so I could go there if I needed.)

But that meant that if you were climbing a hill, and rather than falling back to 1800 rpm to get into the next gear, she fell off to where you got back in at 15-1700 rpm, you were going to do no more than make lots of black smoke. (That is why I had the governor juiced a little, plus it helped on the top end in the tallest gear).

Later experience was with a 8V-92 TA, a turbocharged aftercooled (as well as blown) engine. It had a MUCH better torque rise characteristic and after the 8V-71 (non turbo engine) it always amazed me when it lugged her down to ~13-1500 RPM and she just kept pulling. In fact, I had to overcome some habits developed while driving the 8-71 in order to overcome the urge to shift prematurely. Shifting prematurely would cost you rather than helping you. That engine, however, really wanted about 5 psi of boost before it wanted you to pour the fuel to it. If you feathered it enough to get the 5 psi, you could then mash on it all you wanted. When I trained drivers I termed it "building a fire in her". When you wanted to pass a vehicle on a 2 lane road, you started adding fuel well before you changed lanes and mashed on it.

The Cummins, well there was this one water hose, about 3 inches long that was prone to failure that cost me a couple of those engines. The other one was when a driver went into the pump on his own and turned it way up. I heard stories for years (my truck was rather distinctively striped) about my truck speeding around other trucks on certain famous upgrades. He burnt it up like that and I didn't find out about it until doing a post mortem on the junk engine for trade in.

rmw

 

[rmw]

And I guess the point of all that was back to the OP. Who'd want to drive an automobile if you had to think about all that to drive it?

rmw

 

[WGJ]

In the UK, the Commer TS3 engine was used in 3.5 to 7.5 ton trucks in the 60's. It was a horizontally opposed layout with two pistons per cylinder, a rootes supercharger and was two-stroke.

http://picsdigger.com/keyword/commer ts3/

http://www.youtube.com/watch?v=mfKmkitnqQY

Also check the web for the comprex supercharger. I drove a small-displacement IDI diesel (1.8l, ~108 cu in) fitted with a comprex in about 1985 and, for its time, it was an excellent drive with very good economy. No electronic management involved.

http://en.wikipedia.org/wiki/Pressure_wave_supercharger

Bill

 

[dicer]

swall (Materials) 17 Sep 10 10:05
Detroit Diesels, of course, were two-stroke, supercharged with a Roots blower. But, I don't think any ever made it into light truck use, let alone pass cars.

Sorry I don't know of any other way to quote on this site.
=======================================
The roots blower is not a supercharger on a standard Detroit 2 stroke diesel engine. It is the pump for induction and scavenge.(agree some amount of supercharge can be done) If they desire to supercharge a detroit 2 stroke a turbocharger was added.
And yes a turbocharger is a supercharger, I think the OP is asking about a mechanical supercharger, the problem with a mechanical supercharger is it takes crankshaft power to run it, where the turbocharger doesn't. Any engine that is purposly designed with a mechanical supercharger always benifits from an added turbocharger, if for nothing else but to nulify the load imposed by the mechanical one.
The 2 stroke detroit diesel is a good example, as are some old reciprocating aircraft engines.

 

[tbuelna]

kj16v,

Automotive diesels are now uniformly 4-stroke engines due to emissions, driveability and durability issues.

The 4-stroke does not require any assisted scavenge device like a 2-stroke does.

The 4-stroke rings and liners also tend to be more durable, since there are no ports located in the cylinder walls. The stroke overlap between the oil control ring and compression rings is not severely limited in a 4-stroke, like it is in a 2-stroke.

The thermal loads on a 4-stroke piston/ring pack are also much lower. Since the 4-stroke has half the rate of firing frequency of the 2-stroke.

In theory, a 2-stroke engine should be more efficient than a similar 4-stroke. But for many practical reasons, this is not usually the case. The only exception being, as others pointed out, very large displacement low rpm engines operating at a fixed speed. The current trend seems to favor a 4-stroke at power outputs up to 5000 hp or so.

Hope that helps.
Terry

The trapping/scavenge characteristics of piston ported 2-strokes usually result in a fairly narrow torque curve, unlike a 4-stroke.

 

[sbi]

Turbo's still require crank power!, the exhaust gas is pushed out of the cylinder by the piston, which is connected top the crank, this is where the pressure comes from. it just doe's it more efficiently.

Diesels work fine in cars, it is the driver that wants to leave every stop sign like a drag race that has to drive a SI engine so they get that fast take off, also why there mileage is so poor. This is the #1 reason people trade in there hybrids after a few months be cause they miss the G force leavening the standing start.
Just need to reteach your self how to drive economically!


SBI
Central Ne.,USA

 

[patprimmer]

SBI

No I don't. I just need to accept the fuel cost.

Regards
Pat
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[DanEE]

"This is the #1 reason people trade in there hybrids after a few months be cause they miss the G force leavening the standing start."

Hadn't heard that before, nor experienced it in my 2006 Prius.

Matter of fact it has too much starting torque.. MG2 (the 50KW, 62 horsepower electric motor) produces 295ft-lbs of torque.. Too easy the spin the tires when starting off from a stop, bringing in the traction control..

Toyota agrees.. On the next generation Pruis they reduced the size of MG2.

 

[rmw]

DanEE's reply mirrors my only experience with a hybrid. Given a test ride by a friend (Petroleum E) the most impressive thing about his Toyota Camry Hybrid was the tremendous acceleration away from a standing start. Reminded me of being in a '57 Chevy back in the day. One of the only features that really interested me. I guess I spent too much time driving diesels and just missed the G Forces at take off.

rmw

 

[gruntguru]

Turbo's still require crank power!, the exhaust gas is pushed out of the cylinder by the piston, which is connected top the crank, this is where the pressure comes from. it just doe's it more efficiently.

Not just more efficiently - on a well designed turbo setup, a lot of the energy recovered in the turbine is "blowdown" energy which is free. Blowdown energy is the leftover energy in the cylinder when the exhaust valve first opens. This can be expanded and utilised before the piston starts the exhaust stroke which is where the negative work occurs.