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Renault 2-stroke diesel at 53% effeciency

B

Brian Stirling

Diamond Member
I've seen reports of a new 2-cylinder 2-stroke diesel that Renault is working on that gets about 53% overall efficiency and about 65hp. If that's true that would be by far the highest efficiency numbers I've ever heard and would likely result in a 20%+ increase in overall fuel economy over other diesels and 50% over gas engines.

Anyone know anything more about this? What about other 2-stroke diesels?


Brian
 
I'd guess that it couldn't make emissions numbers, despite its efficiency. Locomotives use 2-stroke diesels for efficiency reasons (both fuel and specific power), and their EPA schedule is relaxed compared to automotive, I believe. If this engine were to be put in a car, it'd likely have to be saddled with some emissions equipment to reduce NOx and particulates that would reduce the efficiency.

Just speculation on my part.
 
I hope that the new Prius will still be available in hatchback form.


BTW- mention of a 2-cycle diesel brings back memories of those Detroit Diesel (2-71,6-71 etc) 2 cycle diesel engines . Dirty,not that efficient but lasted forever.
 
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I don't see how that's possible. Even Stirling Engines built specifically to be as efficient as possible are only about 50% efficient in real life.

I recall (from classes a long time ago) that considering the temperature of burning diesel and air temperature, 50% is pretty much the theoretical limit and we all know that real life engines can't actually get to that point. Frankly, it's amazing how they've managed to push gasoline engines so incredibly high with hybrids.
 
Yeah, 53% does seem to be something I'd need to have demonstrated to believe, but I can see how it might be done. If the exhaust from the engine were fed into a turbine whose function wasn't to boost the intake pressure but to reclaim waste energy I can see an improvement beyond the 43%ish percent a good diesel can produce.

I do wonder about the valve train and the effect running in 2-stroke mode will have on emissions. Back in the day when I had 2-stroke bikes the valving was done mostly with piston ports but with the assistance of reed valves and rotary valves -- my guess is a modern one would not have piston ports but would use camshafts and valves operating 1:1 versus 1:2.

A small engine like this with only about 65hp might seem too small, but if operated in a second generation hybrid 65hp would likely be more than enough for compact to mid sized vehicles. A second gen hybrid that does away with direct drive and instead operates like a full electric car with a generator for range extension and power supplementation could be pretty bad ass even with only a 65hp so long as the battery pack could deliver a few hundred hp.


Brian
 
skyking said:
Here is some more two stroke info. This is an opposed piston design, which has 30% less swept area than a comparable 4 stroke.
http://www.greencarreports.com/news...f-radically-efficient-two-stroke-truck-diesel
Click to expand...


That's VERY interesting! The idea of an opposed engine with two pistons in one cylinder eliminating the need and heat loss of a cylinder head is very interesting. And, since the vibration of one piston will tend to cancel the vibration of the other the total vibration could well be much lower allowing practical engines with just one cylinder and two pistons. Since there is no head the heat loss will be less so that should lower the cooling requirements.

The thing that concerns me is the piston ports for valving. Without a head I guess they're needed but I'd wonder about how long the rings/pistons/cylinders will last with cutouts in the cylinder wall.


Brian
 
Brian Stirling said:
Yeah, 53% does seem to be something I'd need to have demonstrated to believe, but I can see how it might be done. If the exhaust from the engine were fed into a turbine whose function wasn't to boost the intake pressure but to reclaim waste energy I can see an improvement beyond the 43%ish percent a good diesel can produce.
Click to expand...

Turbodiesel engines already do that. The turbo serves to increase power but when you're not using the power, it improves efficiency instead. Of course, you can tune it to favor efficiency more but it's not going to push from 43% to 53%, that's a monumental difference.


It'll be interesting how they implement everything with that 2-stroke engine and how well it works in real life especially with all the emissions control equipment modern diesel requires.
 
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Brian Stirling said:
That's VERY interesting! The idea of an opposed engine with two pistons in one cylinder eliminating the need and heat loss of a cylinder head is very interesting. And, since the vibration of one piston will tend to cancel the vibration of the other the total vibration could well be much lower allowing practical engines with just one cylinder and two pistons. Since there is no head the heat loss will be less so that should lower the cooling requirements.

The thing that concerns me is the piston ports for valving. Without a head I guess they're needed but I'd wonder about how long the rings/pistons/cylinders will last with cutouts in the cylinder wall.


Brian
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Yeah, I'm curious to see how they work the glow plug in there along with all the valves needed without hurting durability. That is a lot of stuff to pack around the side walls and off center. A lot of times direct injectors like to sit directly overhead so they get even coverage. That is impossible with two pistons, they'd have to introduce the fuel from the side. That would result in an uneven distribution. This being two stroke, maybe it goes back to mixing the fuel/air before introducing it to the chamber.

I've read about newer two strokes using traditional oiling techniques to get rid of the mixing of fuel/oil and that is what they are doing here. Can't wait to see more.
 
All compression. Most diesels will start on compression, but in the coldest weather use glow plugs. My cummins has an intake heater that is really not needed, and nothing else.
The VW TDI only glows when it is cold.
My john deere dozer was compression only, or a touch of ether when it was -10f or colder.
None of the commercial truck engines I have driven have glows.
The two strokes I have operated were all Detroit screamers, and ether was used in the cold. How much and what temperature was per the individual engine. Some needed more than others.
 
The opposing piston technology reminds me of Junkers Jumo 207 two stroke diesel engine used in Junkers 86 during and after the Spanish civil war. Germans were able to extract quite a bit of power considering the size of the Jumo engine.
 
ChronoReverse said:
Turbodiesel engines already do that. The turbo serves to increase power but when you're not using the power, it improves efficiency instead. Of course, you can tune it to favor efficiency more but it's not going to push from 43% to 53%, that's a monumental difference.


It'll be interesting how they implement everything with that 2-stroke engine and how well it works in real life especially with all the emissions control equipment modern diesel requires.
Click to expand...

I re-read the original post and the Renault isn't 53% but 50% -- still very impressive.

If they can actually make the emission numbers they need to make AND get the efficiency numbers they're promising this is going to be a game changer. If the Renault 2-cylinder engine makes 50% at 68hp I could see a 2nd gen hybrid using it getting 80mpg. Add about 3.5 m^2 of solar panels to the top and plug in charging at home and such a car might average 120mpg or even 200mpg as a commuter.

It will be very interesting to see what such engine technology would mean for big rig truckers. If the best of them get about 6.5mpg now with a typical load then we could be looking at nearly 10mpg. Then, make them hybrid and we might see 15mpg for a big rig. Similarly, motorhomes and busses might be able to see 20mpg with this tech.


Brian
 
Brian Stirling said:
I re-read the original post and the Renault isn't 53% but 50% -- still very impressive.

If they can actually make the emission numbers they need to make AND get the efficiency numbers they're promising this is going to be a game changer. If the Renault 2-cylinder engine makes 50% at 68hp I could see a 2nd gen hybrid using it getting 80mpg. Add about 3.5 m^2 of solar panels to the top and plug in charging at home and such a car might average 120mpg or even 200mpg as a commuter.

It will be very interesting to see what such engine technology would mean for big rig truckers. If the best of them get about 6.5mpg now with a typical load then we could be looking at nearly 10mpg. Then, make them hybrid and we might see 15mpg for a big rig. Similarly, motorhomes and busses might be able to see 20mpg with this tech.


Brian
Click to expand...

Uh, solar panels on cars are not meant to be used for powering the drive train or even recharging it. Their purpose is just for simple things like keeping the car cool by powering the cabin air fans. Solar panels are too heavy to be of power use on a car. The efficiency is also really low for automotive applications. You're better off removing them from the car for saving weight and cost... Just put them on your house or on top of a parking garage or something.

Also, I'm calling bullshit until I see this in a product. 50% is obscenely high.
 
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This is what the germans wee able to do with an aircraft engine of this design, 80 years ago!
http://www.enginehistory.org/Diesels/CH4.pdf
The notable figures in there are the average BSFC of .35 LB/HP
Compare that to Watsila's current technology, which is already above 50% thermal efficiency at .260 LB/HP.

Fuel consumption at maximum economy is 0.260 lbs/hp/hour. Comparatively, most automotive and small aircraft engines can only achieve BSFC figures in the 0.40-0.60 lbs/hp/hr range and 25-30% thermal efficiency range.
Click to expand...

The added efficiency of the design puts this totally within reach, IMO
 
skyking said:
This is what the germans wee able to do with an aircraft engine of this design, 80 years ago!
http://www.enginehistory.org/Diesels/CH4.pdf
The notable figures in there are the average BSFC of .35 LB/HP
Compare that to Watsila's current technology, which is already above 50% thermal efficiency at .260 LB/HP.



The added efficiency of the design puts this totally within reach, IMO
Click to expand...

It's pretty amazing that they were able to extract 800-1000 shp out of those engines. Later incarnations were even more powerful, with planned power figures in excess 3000 shp at 4400 rpm. That high RPM was unheard of, especially for a diesel.
 
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TridenT said:
Uh, solar panels on cars are not meant to be used for powering the drive train or even recharging it. Their purpose is just for simple things like keeping the car cool by powering the cabin air fans. Solar panels are too heavy to be of power use on a car. The efficiency is also really low for automotive applications. You're better off removing them from the car for saving weight and cost... Just put them on your house or on top of a parking garage or something.

Also, I'm calling bullshit until I see this in a product. 50% is obscenely high.
Click to expand...
Never said the solar panels would directly drive the car. If you have a hybrid with a battery the solar cells would be used to help recharge the battery.

A 30 minute commute to work in mostly city driving might be 10-15 miles and consume 10kWHr of energy without starting the engine. Then, at work, the solar cells provide 2-3 kWHr to help recharge the battery.

So, with plug in power providing 100% of the energy to get to work and solar cells providing 25% of the energy to get home the engine may only be needed for about 15 minutes and less than that if the battery is big enough.

The value of the engine is range extention when away from home or recharge stations. The value of the solar cells is to supplement with cheaper clean energy.


Brian
 
ChronoReverse said:
I don't see how that's possible. Even Stirling Engines built specifically to be as efficient as possible are only about 50% efficient in real life.

I recall (from classes a long time ago) that considering the temperature of burning diesel and air temperature, 50% is pretty much the theoretical limit and we all know that real life engines can't actually get to that point. Frankly, it's amazing how they've managed to push gasoline engines so incredibly high with hybrids.
Click to expand...

The theoretical efficiency of a combustion engine is related to the compression ratio, not directly to the fuel burn temperature. Running some quick, idealized, numbers: 14:1 CR should be around 65% maximum thermal efficiency, 22:1 CR should be around 71% maximum thermal efficiency.

I used the efficiency equation found here: http://en.wikipedia.org/wiki/Diesel_cycle#Maximum_thermal_efficiency

I assumed alpha = 1 (idealized) and air as the working fluid (gamma = 1.4). One might choose a gamma of 1.3, but the results won't change too much.
 
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