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?

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.

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(filter), 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.

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.

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