7 ms·

From the (much better) Reuters article [0]: > The higher the ratio, the more efficiently the engine works, producing better fuel economy and, with the addition

From the (much better) Reuters article [0]: > The higher the ratio, the more efficiently the engine works, producing better fuel economy and, with the addition of a turbo-charger, more power. > Traditionally, design engineers had to fix a gasoline engine's combustion compression ratio, essentially deciding whether to go for power or economy. Everything gets better with higher compression ratio, so where's the compromise? As I understand it, the only reason engine makers don't crank the ratio as high as possible is to avoid knocking. [0] http://www.reuters.com/article/us-autos-japan-nissan-engine-idUSKCN10P0IK?il=0 http://www.reuters.com/article/us-autos-japan-nissan-engine-...

Aelinsaar 10y ago
The drawback is that higher compression ratios require higher octane fuels. Nissan claims to have solved this by some kind of intelligent feedback system that allows them to control compression ratios on the fly. Presumably the compromise there is that it will require more moving parts, be expensive, and may come with issues of its own. Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.
- paulmd 10y ago
  The obvious precedent for variable-pitch blades are variable-pitch propellers on aircraft and helicopters. I don't want to say it's a solved problem for turbos, but there is almost a century's worth of prior art on the topic. That's one of those things that (in hindsight) really makes you wonder what took so long to think up. https://en.wikipedia.org/wiki/Variable-pitch_propeller https://en.wikipedia.org/wiki/Variable-pitch_propeller
  - seanp2k2 10y ago
    Because it has to be cheap and reliable at 1000*C for 200,000 miles over 10 years while constantly accelerating to 280,000RPM and decelerating with no oil or cooling air circulating when the car is stopped. https://garrett.honeywell.com/products/how-a-turbo-works/ https://garrett.honeywell.com/products/how-a-turbo-works/ http://www.epi-eng.com/piston_engine_technology/turbocharger_technology.htm http://www.epi-eng.com/piston_engine_technology/turbocharger...
  - Aelinsaar 10y ago
    That's a challenge, but the thing is a turbo deals with blazing hot exhaust gasses just out of the manifold. A prop is still a marvel of engineering, but it doesn't need to be made of boron carbide to not melt. A better comparison would be variable pitch vanes on jet turbines.
  - _archon_ 10y ago
    Variable geometry turbos are a thing, and have been for some time. The larger trucks and semis use this technology. Typically they are hydraulically controlled.
- shawkinaw 10y ago
  Right, I figured this must actually be an anti-knocking technology. My point was just that the quote implied power and economy are optimized by taking the compression ratio in different directions, which is wrong.
  - Aelinsaar 10y ago
    I see, that's a misunderstanding on me then.
- sliverstorm 10y ago
  That used to be true, but with modern engine design technique you can get higher than ever compression ratios on standard gas...
  - Aelinsaar 10y ago
    There are presumably still limits that this addresses, right? Please correct me if I'm wrong, I'd like to learn.
    - sliverstorm 10y ago
      I suspect it does two things- 1) lets the engine have high compression AND a turbo. Typically a turbo is run with lower compression, because even today nobody can make an engine run 14:1 with a turbo. Speculating, when you floor it the compression might drop to 8:1 and the turbo kicks in; then when you highway cruise, it runs 14:1 for efficiency. 2) lets the little engine still hit big torque numbers at low speeds. This is most likely if the engine is variable stroke, as longer strokes improve low speed torque.
      - Aelinsaar 10y ago
        Ahhhh, those both make a lot of sense. This could be a nice feature on higher-end cars that try to use smaller engines, with more turbos, for the sake of fuel and emissions then?
        sliverstorm 10y ago
        Right, I think it's most interesting in the context of the little-engine-big-turbo archetype.
- 13of40 10y ago
  Maybe the trick would be to have two crank shafts, with two pistons per "cylinder" (or combustion space), and run them slightly out of phase with each other to vary the compression....
tlb 10y ago
Changed the URL from http://www.thedailynewsgrabber.com/nissan-on-gasoline-engine-breakthrough-diesel-obsolete/ http://www.thedailynewsgrabber.com/nissan-on-gasoline-engine..., thanks.
- shawkinaw 10y ago
  I should say I got the link from gervase elsewhere on this thread [0] [0] https://news.ycombinator.com/item?id=12288051 https://news.ycombinator.com/item?id=12288051
maxerickson 10y ago
This article has more technical discussion/speculation and dug up a patent: http://www.motortrend.com/news/infiniti-prepares-worlds-first-variable-compression-engine-for-2018/ http://www.motortrend.com/news/infiniti-prepares-worlds-firs...
sliverstorm 10y ago
High compression ratios produces high combustion temperatures. This leads to the formation of nitrous oxide (NOx). We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man. Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down. One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!
- SigmundA 10y ago
  Well you could do like diesels and use urea injection in the exhaust to neutralize NOx, this add complication, but nothing like this new design.
- asimuvPR 10y ago
  Yes, high compression chambers are tricky and require pistons that incorporate part of the chamber shape on their domes.
- cromulent 10y ago
  Mahle claim 99% reduction of NOx with their Turbulent Jet Ignition system. http://www.f1technical.net/news/20316 http://www.f1technical.net/news/20316
tapeman 10y ago
That article is kind of shitty too. Higher compression ratio = better combustion = more power with less fuel, regardless of turbo. Higher compression will always mean better fuel efficiency. My moms Mazda CX-5 runs a 13.5 compression ratio and gets 27mpg. The power/efficiency trade off appears when you're talking about turbocharged engines. Turbos compress air into the combustion chamber, so when you compress compressed air, you get exponentially compressed air. If you don't adjust the compression ratio for the turbo, you're going to get knock. An engine with a 13.5 compression ratio can run perfectly fine on regular gas, but an engine that runs the same ratio and 20 psi of boost with melt itself even on premium gas. This is a problem for any kind of work vehicle. They almost always have turbos to give them the power to haul their loads with reasonable ease. But this forces the engineers to design the engine with a lower compression ratio, which means at light engine loads, when the turbo isn't doing anything, the engine isn't fulfilling its full potential. It's still compressing air at a low ratio, even though it's not taking in already compressed air. This is where Nissans innovation comes in. The compression ratio will change according to the degree with which the turbo is compressing air. Allowing the engine to run at peak efficiency through the entire range of engine load.
- usrusr 10y ago
  So this only reduces inefficiency while the the engine revs too low for the turbo to kick in? Then it is competing with electrically assisted turbocharging (spin the turbo electrically when there is not enough exhaust pressure, basically a super/turbo hybrid using electric transmission), as both are addressing the same inefficiency. I know where I would put my bets in terms of price, reliability and ease of development.
  - LoSboccacc 10y ago
    Which models are coming out with electrically assisted turbos?
    - stonewhite 10y ago
      Audi SQ7 is coming up with an electrical supercharger and two sequential turbochargers to deliver lagless and variable boost for high performance in all of the rev range. http://www.caranddriver.com/news/2017-audi-sq7-tdi-diesel-photos-and-info-news http://www.caranddriver.com/news/2017-audi-sq7-tdi-diesel-ph...
wepple 10y ago
Under certain conditions (high load, warm day), you'll start hearing a 'pinging' sound on high-compression engines; that's the air/fuel mixture pre-igniting before it is supposed to (before the spark fires) essentially turning the engine into a wannabe diesel and ruining performance/efficiency. There are a few other undesirable things about high-compression. And I just read your message about knocking. same thing. Nevermind.
- semi-extrinsic 10y ago
  Modern engines (as in, post 1989) will sense an engine knock (or a misfire) and go into open cycle ECU mode, ignoring the lambda sensor inputs. It'll run really rough and rich in order to avoid any more knocking, which could seriously damage the engine.
  - fgonzag 10y ago
    And to those curious on how it senses it, they literally stick a microphone in the engine calibrated for the ping (knock) frequency.
    - sdwisely 10y ago
      that actually sounded like such a low tech solution that I wasn't sure if it was some kind of joke that was going over my head. Thanks for sharing, that's actually really fascinating. the patent for anyone interested: https://www.google.com/patents/US4040294 https://www.google.com/patents/US4040294
coredog64 10y ago
Higher compression ratios mean higher temperatures. Higher temperatures means more NOX in the output. As it is cars _already_ have to run richer than stoichiometric in order to keep from melting the catalytic converter. I would expect this will require some extraordinary pollution control measures as well.
- semi-extrinsic 10y ago
  There's plenty of ways to get temperatures down. Bigger intercooler, even refrigerated intercooling, water or water-methanol injection in various forms, going to high alcohol content fuels, etc. Even putting a waste heat recovery unit (WHRU) between the manifold and the catalytic converter is doable. If you want to get really crazy, imagine a WHRU on the manifold in the form of a Rankine cycle where the expander drives a compressor for the air inlet. Like a thermal turbo, if you will, giving you more charge air than NA but with much smaller parasitic power losses than a mechanical turbo.

Aelinsaar 10y ago

The drawback is that higher compression ratios require higher octane fuels. Nissan claims to have solved this by some kind of intelligent feedback system that allows them to control compression ratios on the fly. Presumably the compromise there is that it will require more moving parts, be expensive, and may come with issues of its own. Variability in something like a combustion chamber is a cool idea, so is variability in the angle of turbo vanes. The issue is how you do it, affordably, and in a way that lasts the way that consumers expect from their cars.

paulmd 10y ago
The obvious precedent for variable-pitch blades are variable-pitch propellers on aircraft and helicopters. I don't want to say it's a solved problem for turbos, but there is almost a century's worth of prior art on the topic. That's one of those things that (in hindsight) really makes you wonder what took so long to think up. https://en.wikipedia.org/wiki/Variable-pitch_propeller https://en.wikipedia.org/wiki/Variable-pitch_propeller
- seanp2k2 10y ago
  Because it has to be cheap and reliable at 1000*C for 200,000 miles over 10 years while constantly accelerating to 280,000RPM and decelerating with no oil or cooling air circulating when the car is stopped. https://garrett.honeywell.com/products/how-a-turbo-works/ https://garrett.honeywell.com/products/how-a-turbo-works/ http://www.epi-eng.com/piston_engine_technology/turbocharger_technology.htm http://www.epi-eng.com/piston_engine_technology/turbocharger...
- Aelinsaar 10y ago
  That's a challenge, but the thing is a turbo deals with blazing hot exhaust gasses just out of the manifold. A prop is still a marvel of engineering, but it doesn't need to be made of boron carbide to not melt. A better comparison would be variable pitch vanes on jet turbines.
- _archon_ 10y ago
  Variable geometry turbos are a thing, and have been for some time. The larger trucks and semis use this technology. Typically they are hydraulically controlled.
shawkinaw 10y ago
Right, I figured this must actually be an anti-knocking technology. My point was just that the quote implied power and economy are optimized by taking the compression ratio in different directions, which is wrong.
- Aelinsaar 10y ago
  I see, that's a misunderstanding on me then.
sliverstorm 10y ago
That used to be true, but with modern engine design technique you can get higher than ever compression ratios on standard gas...
- Aelinsaar 10y ago
  There are presumably still limits that this addresses, right? Please correct me if I'm wrong, I'd like to learn.
  - sliverstorm 10y ago
    I suspect it does two things- 1) lets the engine have high compression AND a turbo. Typically a turbo is run with lower compression, because even today nobody can make an engine run 14:1 with a turbo. Speculating, when you floor it the compression might drop to 8:1 and the turbo kicks in; then when you highway cruise, it runs 14:1 for efficiency. 2) lets the little engine still hit big torque numbers at low speeds. This is most likely if the engine is variable stroke, as longer strokes improve low speed torque.
    - Aelinsaar 10y ago
      Ahhhh, those both make a lot of sense. This could be a nice feature on higher-end cars that try to use smaller engines, with more turbos, for the sake of fuel and emissions then?
      - sliverstorm 10y ago
        Right, I think it's most interesting in the context of the little-engine-big-turbo archetype.
13of40 10y ago
Maybe the trick would be to have two crank shafts, with two pistons per "cylinder" (or combustion space), and run them slightly out of phase with each other to vary the compression....

tlb 10y ago

Changed the URL from http://www.thedailynewsgrabber.com/nissan-on-gasoline-engine-breakthrough-diesel-obsolete/ http://www.thedailynewsgrabber.com/nissan-on-gasoline-engine..., thanks.

shawkinaw 10y ago
I should say I got the link from gervase elsewhere on this thread [0] [0] https://news.ycombinator.com/item?id=12288051 https://news.ycombinator.com/item?id=12288051

maxerickson 10y ago

This article has more technical discussion/speculation and dug up a patent: http://www.motortrend.com/news/infiniti-prepares-worlds-first-variable-compression-engine-for-2018/ http://www.motortrend.com/news/infiniti-prepares-worlds-firs...

sliverstorm 10y ago

High compression ratios produces high combustion temperatures. This leads to the formation of nitrous oxide (NOx). We have a lot of techniques to improve mpg that increase NOx. If you can figure out how to easily inhibit NOx formation inside the combustion chamber you could be a rich man. Incedentally this is one way direct gasoline injection can improve economy. The injector sprays directly into the cylinder, and can do so in a way that forms a little donut of air/fuel mix that is insulated from the walls by a layer of air. It is then ignited. The air barrier helps keep combustion temperatures down. One last thing, really high compression tends to result in a chamber that is very flat and narrow, which can counterproductively cause hotspots and incomplete combustion because the flame front is restricted. This can be fixed with undersquare pistons with longer travel, but that leads to big, low-power, slow-revving engines, like diesels!

SigmundA 10y ago
Well you could do like diesels and use urea injection in the exhaust to neutralize NOx, this add complication, but nothing like this new design.
asimuvPR 10y ago
Yes, high compression chambers are tricky and require pistons that incorporate part of the chamber shape on their domes.
cromulent 10y ago
Mahle claim 99% reduction of NOx with their Turbulent Jet Ignition system. http://www.f1technical.net/news/20316 http://www.f1technical.net/news/20316

tapeman 10y ago

That article is kind of shitty too. Higher compression ratio = better combustion = more power with less fuel, regardless of turbo. Higher compression will always mean better fuel efficiency. My moms Mazda CX-5 runs a 13.5 compression ratio and gets 27mpg. The power/efficiency trade off appears when you're talking about turbocharged engines. Turbos compress air into the combustion chamber, so when you compress compressed air, you get exponentially compressed air. If you don't adjust the compression ratio for the turbo, you're going to get knock. An engine with a 13.5 compression ratio can run perfectly fine on regular gas, but an engine that runs the same ratio and 20 psi of boost with melt itself even on premium gas. This is a problem for any kind of work vehicle. They almost always have turbos to give them the power to haul their loads with reasonable ease. But this forces the engineers to design the engine with a lower compression ratio, which means at light engine loads, when the turbo isn't doing anything, the engine isn't fulfilling its full potential. It's still compressing air at a low ratio, even though it's not taking in already compressed air. This is where Nissans innovation comes in. The compression ratio will change according to the degree with which the turbo is compressing air. Allowing the engine to run at peak efficiency through the entire range of engine load.

usrusr 10y ago
So this only reduces inefficiency while the the engine revs too low for the turbo to kick in? Then it is competing with electrically assisted turbocharging (spin the turbo electrically when there is not enough exhaust pressure, basically a super/turbo hybrid using electric transmission), as both are addressing the same inefficiency. I know where I would put my bets in terms of price, reliability and ease of development.
- LoSboccacc 10y ago
  Which models are coming out with electrically assisted turbos?
  - stonewhite 10y ago
    Audi SQ7 is coming up with an electrical supercharger and two sequential turbochargers to deliver lagless and variable boost for high performance in all of the rev range. http://www.caranddriver.com/news/2017-audi-sq7-tdi-diesel-photos-and-info-news http://www.caranddriver.com/news/2017-audi-sq7-tdi-diesel-ph...

wepple 10y ago

Under certain conditions (high load, warm day), you'll start hearing a 'pinging' sound on high-compression engines; that's the air/fuel mixture pre-igniting before it is supposed to (before the spark fires) essentially turning the engine into a wannabe diesel and ruining performance/efficiency. There are a few other undesirable things about high-compression. And I just read your message about knocking. same thing. Nevermind.

semi-extrinsic 10y ago
Modern engines (as in, post 1989) will sense an engine knock (or a misfire) and go into open cycle ECU mode, ignoring the lambda sensor inputs. It'll run really rough and rich in order to avoid any more knocking, which could seriously damage the engine.
- fgonzag 10y ago
  And to those curious on how it senses it, they literally stick a microphone in the engine calibrated for the ping (knock) frequency.
  - sdwisely 10y ago
    that actually sounded like such a low tech solution that I wasn't sure if it was some kind of joke that was going over my head. Thanks for sharing, that's actually really fascinating. the patent for anyone interested: https://www.google.com/patents/US4040294 https://www.google.com/patents/US4040294

coredog64 10y ago

Higher compression ratios mean higher temperatures. Higher temperatures means more NOX in the output. As it is cars _already_ have to run richer than stoichiometric in order to keep from melting the catalytic converter. I would expect this will require some extraordinary pollution control measures as well.

semi-extrinsic 10y ago
There's plenty of ways to get temperatures down. Bigger intercooler, even refrigerated intercooling, water or water-methanol injection in various forms, going to high alcohol content fuels, etc. Even putting a waste heat recovery unit (WHRU) between the manifold and the catalytic converter is doable. If you want to get really crazy, imagine a WHRU on the manifold in the form of a Rankine cycle where the expander drives a compressor for the air inlet. Like a thermal turbo, if you will, giving you more charge air than NA but with much smaller parasitic power losses than a mechanical turbo.