RE: Infiniti's variable compression ratio engine
Discussion
PHMatt said:
Surely the most simplistic way of making petrol engines more efficient is better use of the cylinders. IE, if you're pootling along why not drop down to 2, or even just the 1 cylinder.
I have a 3.0D BMW. Although it claims it'll do 47mpg on the combined run it's more like 38mpg at best. It could easily do better if it shut down 3 cylinders when you drop it into eco mode rather than whatever it actually does which hardly saves fuel but makes it painfully slow.
Different manufacturers have different perspectives on this. For example, BMW maintain that if you have bought a car with a 6 cylinder engine in, it's because you want a 6 cylinder engine so they have no plans to offer CDA on them. For now anyway.I have a 3.0D BMW. Although it claims it'll do 47mpg on the combined run it's more like 38mpg at best. It could easily do better if it shut down 3 cylinders when you drop it into eco mode rather than whatever it actually does which hardly saves fuel but makes it painfully slow.
The benefits of CDA have been heavily oversold over the years. It's fine for very large engines, however smaller engines there are limited thermodynamic improvements to be had when friction and the like are taken into account. On top of that, the NVH aspect can't be ignored with the level of refinement some of these cars are supposed to provide. Making the change imperceptible to the driver costs a fortune in palliatives or active engine mounts or both.
leon9191 said:
Cylinder deactivation is actually quite complex, its not a case of just cutting the spark and fuel you have to be able to remove any compression from the deactivated cylinder or stop them turning altogether so either a complex valve operation for the entire engine or a 2 piece crank with a clutch type set up.
an n-piece crank would also mean complex valve operation, not to mention trouble resynching the crank when cylinders are reactivated, or you'll end up with a different firing sequence and very different vibrations in the engine.And even if you open up the valves all the time, the inactive cylinders will still act like an air pump and incur friction losses
They may be integrating the equivalent of a balance shaft into the tech.
Modern 4 cylinders tend to have one or more balance shafts spinning away inside the engine, with their associated bearings and gear / cambelt drives.
My 90's Mitsubishi has 2 spinning at different speeds, and IIRC Toyota had a pair running in the sump in their 2.4 litre.
They take up space, and cost some friction - probably as much as this VCR tech.
Just idle speculation...
Modern 4 cylinders tend to have one or more balance shafts spinning away inside the engine, with their associated bearings and gear / cambelt drives.
My 90's Mitsubishi has 2 spinning at different speeds, and IIRC Toyota had a pair running in the sump in their 2.4 litre.
They take up space, and cost some friction - probably as much as this VCR tech.
Just idle speculation...
Vitorio said:
leon9191 said:
Cylinder deactivation is actually quite complex, its not a case of just cutting the spark and fuel you have to be able to remove any compression from the deactivated cylinder or stop them turning altogether so either a complex valve operation for the entire engine or a 2 piece crank with a clutch type set up.
an n-piece crank would also mean complex valve operation, not to mention trouble resynching the crank when cylinders are reactivated, or you'll end up with a different firing sequence and very different vibrations in the engine.And even if you open up the valves all the time, the inactive cylinders will still act like an air pump and incur friction losses
I thought that Merc did a twin crank v8 so they could shut down one bank of cylinders altogether but it was only on the very top of the range cars and how effective it was I couldn't say. How you reactivate and resynch the second bank must be a cleaver bit of engineering.
leon9191 said:
Exactly my thoughts, its referred to as pumping losses which is hilarious in my childish mind.
I thought that Merc did a twin crank v8 so they could shut down one bank of cylinders altogether but it was only on the very top of the range cars and how effective it was I couldn't say. How you reactivate and resynch the second bank must be a cleaver bit of engineering.
Assuming each bank operates just like an I4, you wouldnt really need to re-sync it i think, although there is bound to be some vibrations coming out of an i4..I thought that Merc did a twin crank v8 so they could shut down one bank of cylinders altogether but it was only on the very top of the range cars and how effective it was I couldn't say. How you reactivate and resynch the second bank must be a cleaver bit of engineering.
zeppelin101 said:
Different manufacturers have different perspectives on this. For example, BMW maintain that if you have bought a car with a 6 cylinder engine in, it's because you want a 6 cylinder engine so they have no plans to offer CDA on them. For now anyway.
Just like true power that can't be compressed etc... 
J4CKO said:
Anyone else think its a few years too late ?
The problem for IC engines is they are too complex and inefficient anyway, this adds even more moving parts.
I think the rise of the EV will put paid to much new development in IC engines fairly soon, this feels a bit like improvements to VHS video recorders.
Disagree theirs a reason we're still using these engines today and it's not because they are too complex and inefficient.The problem for IC engines is they are too complex and inefficient anyway, this adds even more moving parts.
I think the rise of the EV will put paid to much new development in IC engines fairly soon, this feels a bit like improvements to VHS video recorders.
Vitorio said:
annodomini2 said:
I thought this was the need from the '80s with Carburettor or indirect injection setups.
With direct injection the fuel is not in the cylinder until needed, hence no pinking. Also this has a charge cooling effect AFAIU.
You effectively achieve variable compression with a Turbocharger for most of the cycle anyway.
I may have missed something obvious, but that was my understanding.
Injection still takes time, it not an instantanious "poof, there is now fuel in your cylinder" effect.With direct injection the fuel is not in the cylinder until needed, hence no pinking. Also this has a charge cooling effect AFAIU.
You effectively achieve variable compression with a Turbocharger for most of the cycle anyway.
I may have missed something obvious, but that was my understanding.
And turbo/super charging doesnt effect the CR, only the total pressure at the top of the stroke, which is why often turbo engines have a lower CR to bring that final pre-spark pressure back within non-pinging limits
leon9191 said:
PHMatt said:
Surely the most simplistic way of making petrol engines more efficient is better use of the cylinders. IE, if you're pootling along why not drop down to 2, or even just the 1 cylinder.
I have a 3.0D BMW. Although it claims it'll do 47mpg on the combined run it's more like 38mpg at best. It could easily do better if it shut down 3 cylinders when you drop it into eco mode rather than whatever it actually does which hardly saves fuel but makes it painfully slow.
Cylinder deactivation is actually quite complex, its not a case of just cutting the spark and fuel you have to be able to remove any compression from the deactivated cylinder or stop them turning altogether so either a complex valve operation for the entire engine or a 2 piece crank with a clutch type set up. I have a 3.0D BMW. Although it claims it'll do 47mpg on the combined run it's more like 38mpg at best. It could easily do better if it shut down 3 cylinders when you drop it into eco mode rather than whatever it actually does which hardly saves fuel but makes it painfully slow.
peter450 said:
J4CKO said:
Anyone else think its a few years too late ?
The problem for IC engines is they are too complex and inefficient anyway, this adds even more moving parts.
I think the rise of the EV will put paid to much new development in IC engines fairly soon, this feels a bit like improvements to VHS video recorders.
Disagree theirs a reason we're still using these engines today and it's not because they are too complex and inefficient.The problem for IC engines is they are too complex and inefficient anyway, this adds even more moving parts.
I think the rise of the EV will put paid to much new development in IC engines fairly soon, this feels a bit like improvements to VHS video recorders.
Now, I know we all love the IC but it is on its way out, its noisy, inefficient, polluting, needs lots of cooling etc etc.
As the battery tech and infrastructure improves, which it is doing, as people see others using them and quite happily managing all their transport needs, as the charging speed improves, IC engines will be dropped like a stone, not yet, but it is coming.
I know it relies on clean electricity but whatever you do, you can run an EV on electricity from burning crude or renewables, you cant run an IC on anything other than fossil fuels or some other polluting concoction.
I am not sure why its such a surprise, the IC will be around for a good while, for ever in certain applications, classics and people who still want one, but for the bulk of personal car transport, the IC is on its way.
PHMatt said:
and say in 10 years time, 60-70% of cars on the road are EV's
I am certain that it would be physically impossible to cover the increase in electric power demand if EVs would really spread at the rate of zero to 60% in ten years. Electricity prices would go through the roof promptly and EVs lose a lot of the sex appeal.Battery manufacturing capacity is another bottleneck.
Turbobanana said:
Effjay said:
Turbobanana said:
By extension, does this also mean the engine is of variable capacity?
Which may also mean it could infer benefits where engine capacity is key, such as class Motorsport, taxation classes etc
I may be wrong but as the overall piston stroke will still be the same, the capacity will remain the same?Which may also mean it could infer benefits where engine capacity is key, such as class Motorsport, taxation classes etc
The diagram seems a little confusing too: surely the "power" setting is the one with the higher compression ratio and the "efficiency" the one with the lower?
And the article states that the control shaft rotates in the combustion chamber - which it doesn't (it appears to be in the crankcase. The combustion chamber is where the combustion takes place).
Happy to be shot down by a better explanation as I'm no engineer.
Mazda Skyactiv is already 14:1 on their petrol units with high pressure direct injection (no HCCI). For Skyactiv 2 they are aiming for 18:1 and HCCI operation in certain load-speed regions. If they can do it it will be very efficient indeed.
Vitorio said:
annodomini2 said:
I thought this was the need from the '80s with Carburettor or indirect injection setups.
With direct injection the fuel is not in the cylinder until needed, hence no pinking. Also this has a charge cooling effect AFAIU.
You effectively achieve variable compression with a Turbocharger for most of the cycle anyway.
I may have missed something obvious, but that was my understanding.
Injection still takes time, it not an instantanious "poof, there is now fuel in your cylinder" effect.With direct injection the fuel is not in the cylinder until needed, hence no pinking. Also this has a charge cooling effect AFAIU.
You effectively achieve variable compression with a Turbocharger for most of the cycle anyway.
I may have missed something obvious, but that was my understanding.
And turbo/super charging doesnt effect the CR, only the total pressure at the top of the stroke, which is why often turbo engines have a lower CR to bring that final pre-spark pressure back within non-pinging limits
Vitorio said:
PHMatt said:
The interesting thing is, if this did happen, and say in 10 years time, 60-70% of cars on the road are EV's, would the tax relief continue? I doubt it.
Off course not, tax reliefs for hybrids/EVs in the netherlands are already being wound back, the eco diesel is no longer able to get any kind of financial bonus.If anything, road tax or initial tax when buying the vehicle will go up, since income from petrol tax will go down.
...so in the future it will be "discovered" that EV have poisionous batteries which need to be replaced every few years, very bad for everyone... stick with petrol etc etc
Mind you, road pricing will be a certainty by then so there will be no more tax to pay...
Amanitin said:
PHMatt said:
and say in 10 years time, 60-70% of cars on the road are EV's
I am certain that it would be physically impossible to cover the increase in electric power demand if EVs would really spread at the rate of zero to 60% in ten years. Electricity prices would go through the roof promptly and EVs lose a lot of the sex appeal.Battery manufacturing capacity is another bottleneck.
60-70% in 10 years is totally unrealistic, it takes 15-20 years to switch a national fleet over, and at the moment there is only battery production for about 1-2% of vehicle production. That is scaling up fast but it'll take a decade plus to be able to even build 60% of the required vehicle volume as EV's
if only Nissan had thought of that!Gassing Station | General Gassing | Top of Page | What's New | My Stuff