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

 

[patprimmer]

But extra restriction to exhaust flow slows the blow down therefore leaving more residual pressure during the exhaust stroke.

Regards
Pat
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[gruntguru]

Hi Pat. I didn't say it was all free, just that a significant portion of it is free energy. During the initial phase of blowdown, the flow through the exhaust valve is choked and the higher pressure in the exhaust manifold due to the turbine does not reduce the flow.

 

[WGJ]

Given the amount of after-treatment methods and devices that are finding their way onto Euro Stage-V diesel engines, plus the associated incremental electronics and software, I wonder whether a blown 2-stroke, with its initial 'poorer' emissions, might be a viable improved power-to-weight ratio opportunity - with all the same/similar after-treatment effort?

Anyone got an idea?

Bill

 

[HRHtex]

Nobody seems to have mentioned what is possibly the main problem with 2-stroke valved engines - both diesel and SI.
The problem being that the camshaft must run at crankshaft speed - not half crankshaft speed as with a 4-stroke. So even at a moderate rpm like 3000/4000 the valve gear is working at racing engine speeds.
Ideas like having two cams running at half speed and opening valves on alternate strokes similarly run into valve speed problems. The valve problem is probably the main reason Junkers/Napier etc. went for the opposed-piston/two-crank layout.
If it were not for the valve speed problem I suspect 2-stroke diesels and SI engines would be a lot more common.

 

[drwebb]

A trivial example- I have a Cox Sandblaster somewhere in my basement, a 2T diesel car (albeit methanol/nitro fueled with 0.049" displacement). I recall it has only ever started in the reverse direction for unknown reason.

 

[dgallup]

Quote:
"Beg to differ, ships do have emissions standards, International Maritime Organization has imposed standards"

Yeah, they are going to reduce sulfur from 4.5% max to 3.5% max in 2012. Inspect emissions once every 5 years. Once they are international waters I'm sure they are right back to burning bunker oil and jacking up the injection timing. Toothless laws with no enforcement.

 

[rmw]

drwebb, I had forgotten about the blasted things running backward as well as they run forward. I have seen 2 Detroits do that. I had always heard that they would, but I saw 2 of them do it with my own eyes (and paid for the damage to other driven components not designed to run backwards like AC compressors myself too.)

rmw

 

[SMOKEY44211]

Diahatsu markets a two stroke diesel. Claim it gets 100mpg. I am currently fabricating a three cyl. two stroke diesel but air in through the poppet valves, exhaust through the sleeve ports. Theory is more uniform combustion chamber temp. Possibly no need for coolant in the head. Two lobes per valve position slows cam down to half crank speed. I have a fueling strategy that should allow for HCCI operation. We'll see. ------Phil

 

[LadaTrouble]

''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"

Mazda Capella? A very strange supercharger that is not self explanatory when you have it in your hands.Physically there is no separation between inlet and exhaust....but it does seem to work.It's belt driven off the back of the alternator,and belt tension is critical - black soot on the engine side of the airfilter is a pretty dramatic symptom of a slipping belt.

Most 2 stroke diesels should have a dephaser in the injector pump drive - the TS3 would switch to reverse running if the idle speed was too low.

 

[HRHtex]

Smokey - sounds like an interesting project - however the two-lobes-instead-of-one idea probably doesn't solve the valve speed problem. The two stroke engine needs an opening duration of about 120 crankshaft degrees - on a half-speed cam this is a cam angle of about 60 degrees. This is a very short duration and it would be difficult to get any useful amount of valve lift over such a short duration.
I note that on the Daihatsu power/torque graph the maximum power is at a very low 3500RPM - it looks like the Daihatsu's RPM is limited by valve speed problems.

http://www.daihatsu.com/brand/motorshow/frankfurt99/s2cd/photo/img/08e.pdf

 

[tbuelna]

How about both 2 and 4 stroke in one engine:

https://www.ricardo.com/en-gb/News-...-to-build-switchable-two-four--stroke-engine/

This example is GDI, but there's no reason it couldn't be CI diesel.

Terry

 

[TDIMeister]

AVL and Ricardo, among other engine consulting houses, have been developing small 2-stroke compression ignition engines. FEV can be counted in this company as Ecomotor's founder Prof. Peter Hofbauer incubated his OPOC engine idea while working there.

A 2-stroke Diesel loses much of its simplicity advantages compared to small gasoline 2-strokes since a valvetrain (opposed piston engines excepted) and wet sump lubrication are usually needed. In exchange you double the frequency of combustion heat flux (read higher thermal stress) but you don't get double the specific output.

Emissions is not a major problem now owing to ultra high-pressure piezo common rail injecion, copious amounts of EGR and modern aftertreatment. Ported liner lubrication, oil consumption and attendent emissions is probably still the biggest issue. This can be solved, as Toyota and Ricardo have done, by eliminating the ported liner and using poppet valves for both intake and exhaust in a 2-stroke design.

 

[HRHtex]

Toyota and Ricardo really haven't solved the problem with 2-stroke engines with poppet valves - they are still very RPM-limited - and they still need scavenging blowers.

Credit where credit is due. Evidence would suggest that the Hofbauer/FEV/OPOC engine was inspired (or possibly plagiarised) from the pre-war NSU opposed piston engine.

 

[TDIMeister]

2-stroke engines SI or CI, will ALWAYS need forced scavenging by their inherent operation; the loadings of a CI engine is just not amenable to rolling bearings in the bottom end with oil vapour lubrication, whilst crankcase scavenging presents other problems of emissions and pre-ignition in a Diesel engine. A scavenging blower is not a big deal, especially when forced induction in the form of turbochargers is now ubiquitous in Diesel engines of all sizes.

There is no particular basis in the combustion process that prevents a 2-stroke Diesel from operating as high of an RPM as a 4-stroke Diesel counterpart; however, the truncated expansion from early exhaust port/valve opening is usually not far from the end of all heat-release from combustion...

Toyota and Ricardo abandoned researching 2-stroke CI engines over a decade ago (the much more recent poppet-valved Ricardo 2/4Sight was spark ignited and not the project I'm referring to), just as development was taking off with modern injection systems and combustion development. Even if 2-stroke Diesels were limited to, say, 3500 RPM, that suits an application like a range-extender just fine. The problem is that a poppet-valved 2-stroke would have its valvetrain operating like a 4-stroke at 7000 RPM. Once again, the RPM limitation in this case has nothing to do with the combustion development.

 

[HRHtex]

Oddly enough poppet-valve two strokes will run without a scavenging blower of any kind. Toyota reported that their six-cylinder poppet valve 2-stroke would run without a blower - but they gave no details of how well it ran.

I know from personal experience with a modified 3-cylinder Charade engine (with a crank-speed cam) that 2-stroke operation without a blower is possible. The engine ran but not very well. There was a lot of spitting back out of the intakes - I thought motorcycle-style reed valves might help but never tried it.
Without a blower the induction is basically powered by the exhaust rushing out and drawing the new charge in.

One reason I thought "Smokey's" project was interesting was that the exhaust-powered scavenging should be a lot more effective with his suggested uniflow type of layout. His engine may run quite well with reed valves and no blower.

 

[L4189]

Just think of a 4 stroke diesel as a 2 stroke that uses its piston to do the scavenging. And what's the matter with developing maximum torque at low speed. Avoids costly and compilcated speed reduction transmissions.

 

[PJGD]

The issue with poppet valve 2-strokes is achieving good scavenging efficiency. With a conventional diesel combustion chamber; 4 inward-opening valves with central vertical injector, it is difficult if not impossible to direct the intake flow to loop down the cylinder on one side, and then back up the other side and out of the exhaust; it has every incentive to short-circuit straight out the exhaust.

To get reasonable scavenge efficiency, you have to go with downdraft ports on the inlet side (which is what Ricardo did for their "Flagship" SI poppet-valve 2-stroke), but this is formidable to package around the injector.

You can argue that today when all engines use EGR (and usually lots of it) that good scavenging is not so important, but hot residuals are only ~50% as effective as cooled EGR at NOx mitigation, so you really want cooled EGR even in a 2-stroke where the combustion temperatures are lower (than in a 4-stroke) anyway. Plus, you still need to get the fresh air for the next cycle in on top of the residuals, and there is not much time between EVC and IVC.

So, with a 2-stroke diesel, you need to have directed intake flow for good scavenging efficiency, but you will still likely need well-controlled swirl to get good combustion efficiency. Achieving both requirements is not easy with a conventional chamber.

PJGD

 

[SMOKEY44211]

For what it's worth the valve lift is .190 intake/scavange is 80 deg. crank rotation. (40 deg. cam) With 4 valves should be sufficient valve curtain to provide at least 75% fresh air charge. I've modified a couple of 4 stroke diesels to run on HCCI combustion process. I've been able to get the same power levels without the need for a turbo and nox is a lot lower. Very noisy though. Fuel economy is the best I've ever seen. Hopefully this two stroke will eclipse that.------Phil

 

[TDIMeister]

@SMOKEY44211: Any videos or publications of your work you can share?

 

[HRHtex]

Smokey - I too would like to see videos and more details etc.

Does "without the need for a turbo" mean that your engine will run without any scavenging blower?

Have you tried (or considered) an SI version of your engine?

All 2-strokes are loud. I found that a test 200cc Yamaha twin with no mufflers was actually far louder than a 4-litre 6 without mufflers.