33 replies to this topic

[mariner]

As of now, politics aside the US auto industry is required to get to 54 miles per US gallon very soon - a tough challenge.

 

I had never heard of, or thought of this aproach to boosting petrol mpg but I think it makes sense in principle.

 

http://www.dragzine....what-that-means

 

And more from Mark Phalen of the Detroit Free Press

 

http://www.freep.com...eers/100716174/

 

The argument of extra price vs extra mpg being break-even at small price increments for very high octane is attractive.

 

Maybe the real problem il be the oil companies willingness to invest vast sums into refining as teh long term demand trend for gasoline becomes uncertain?

 

Anyway if it happens imagine all those 15:1 Chevy Big Blocks cruising cheaply again!

[gruntguru]

Water injection is worth at least a few octane points and can be controlled so you only get the octane boost when you need it - under load.

http://www.bosch-mob...ater-injection/

[Greg Locock]

Water injection is one of those ideas that seems obvious. But there are reasons why it hasn't taken off for OEMs. One of the chief ones is mould etc in the lines. Seems stupid, but there you are.

 

Roughly a decade ago in Oz the OEMs pointed out that our crap fuel was preventing better engine tunes, and lo and behold (after much whingeing) they did raise the octane and get rid of the high sulphur diesel fuels.

[munks]

I only vaguely understand the workings of an ICE, but wouldn't a miniscule amount of chlorine or alcohol take care of any mold problem?

[Magoo]

Water injection is good for a power increase but increases in efficiency are problematic as in the end, you are using BTUs to boil water. 

 

Ethanol or methanol + water injection has caloric value, but then it is a secondary fuel and I have no idea how the EPA et al would score it. 

[Magoo]

As of now, politics aside the US auto industry is required to get to 54 miles per US gallon very soon - a tough challenge.

 

 

 

Until Trump is dragged away in leg irons, I believe the 54 mpg federal mandate is on hold. At last report, EPA headquarters at Federal Triangle is being converted into a working 19th century coal mine. 

[Sisyphus]

As Magoo rightly notes, no point in getting too excited about the 54 mpg mandate while Trump remains in office.

 

But while water injection allows higher compression ratios without knocking (which allows higher thermodynamic efficiency) it has limits to its effectiveness.  It isn't going to make a 30 mpg vehicle get 54 mpg, for example.  But it can help somewhat and with a turbo you have an easier means of controlling the effective compression ratio since you can easily adjust the boost pressure.

 

The problem is that to utilize the benefit, you must keep your water bottle filled and that has been a problem in the past.  The original 1962 turbo Olds relied on water injection but people would not bother to keep the tank topped up which then damaged a lot of engines from detonation.  With today's sensors, you could avoid damaging your engine but then you wouldn't be able to take advantage of the higher compression ratio.

 

A similar issue exists with urea injection on diesels and apparently, people do keep those tanks topped up although it is a big tank (at least on some models) which lasts until you are called into the dealership for service.  I suppose that is how they overcome driver inattention.

[gruntguru]

As Magoo rightly notes, no point in getting too excited about the 54 mpg mandate while Trump remains in office.

 

But while water injection allows higher compression ratios without knocking (which allows higher thermodynamic efficiency) it has limits to its effectiveness.  It isn't going to make a 30 mpg vehicle get 54 mpg, for example.  But it can help somewhat and with a turbo you have an easier means of controlling the effective compression ratio since you can easily adjust the boost pressure.

 

The problem is that to utilize the benefit, you must keep your water bottle filled and that has been a problem in the past.  The original 1962 turbo Olds relied on water injection but people would not bother to keep the tank topped up which then damaged a lot of engines from detonation.  With today's sensors, you could avoid damaging your engine but then you wouldn't be able to take advantage of the higher compression ratio.

 

A similar issue exists with urea injection on diesels and apparently, people do keep those tanks topped up although it is a big tank (at least on some models) which lasts until you are called into the dealership for service.  I suppose that is how they overcome driver inattention.

I agree with everything you say but you could replace the words "water injection" with "higher octane fuel" and all those negatives still apply. Water injection however has at least two advantages over higher octane fuel - it is cheaper and you don't need to use it all the time. High octane fuel is essentially wasted at idle and light load.

Edited by gruntguru, 10 July 2017 - 22:55.

[RogerGraham]

Until Trump is dragged away in leg irons, I believe the 54 mpg federal mandate is on hold. At last report, EPA headquarters at Federal Triangle is being converted into a working 19th century coal mine. 

 

If a large state like California decides to keep the higher mpg standards (which, IIRC, they can do independently from the feds, and have said they would do), doesn't that effectively become a national standard?

[Lee Nicolle]

Having spent a month in the UK in a Kia turbo diesel renter that got a best of 55mpg highway I would hate to see what they would come up with. City seemed to be high 30s and I suspect about 10mpg in metro London where you spend most of the time stopped avoiding buses!

This is on a 1.2 litre  MANUAL smallish  4 seat car which was actually quite good on the motorway but less than ok on rural roads. Or traffic. And ofcourse diesel is dirty, you can see and smell it as many UK cars are diesel.

Plus I suspect the endurance will be quite suspect.

How many manual cars in the US?  How would Americans take to  manual cars with a narrow power band?

Not well I feel. I know I am very glad to be back driving real cars!!

 

As for high octane?  You can make better power and probably cleaner as well but 54mpg? 

[Joe Bosworth]

The title of this thread is,

"higher octane fuels to get to 54 mpg."

Guys and girls, we are dreaming.  Higher octane fuels will almost never allow us to get to the 2025 CAFE standard.

 

The standard of today is 35.5 mpg.  54 mpg is an increase of 52.1% over today's reality.

 

The effect of change of octane number is tightly controlled by our knowledge of the Otto Cycle which has been fully understood by the basic Laws of Thermodynamics.

 

Increases in octane numbers by themselves do not improve fuel efficiency 100 octane fuel in your car which has been optimised to burn 90 octane will make no difference other than if your car has variable timing sensors in which case you will see fuel use improvements of about 8%.

 

The real value of high octane fuels is that they allow compression ratios to be increased.  The effect of increasing compression ratios can be estimated from formulas developed from the thermodynamic characteristics of fuel compression and burning with well known boundaries.

 

I have not tried to calculate the average compression ratio of vehicles today but it is certainly above 10 to 1.  A lot of cars list values above 11 to 1 and high performance motor cycles are in the 12.5 to 1 range.

 

The articles quoted in the opening messages of this thread speak of 15 to 1 CR being possible or likely. For this discussion I will accept that estimate.

 

The important piece of science that comes from this is that raising compression ratios from 10 to 1 to 15 to 1 only provided a combustion efficiency improvement of some 13%; certainly a long way from the 52% required.  If today's average CR is closer to  11 to 1 then the efficiency improvement to 15 to 1 is only 8.3%.

 

Reaching the required CAFE in less than 10 years is going to take an enormous change to the technology mix of our vehicles which really should be the subject of a re-titled thread.

[Greg Locock]

 

 

Increases in octane numbers by themselves do not improve fuel efficiency 100 octane fuel in your car which has been optimised to burn 90 octane will make no difference other than if your car has variable timing sensors in which case you will see fuel use improvements of about 8%.

 

 

The back half of that sentence doesn't agree with the front half.

 

I don't think anybody claimed that octane alone would get the fleet to 54 mpg. But it allows a useful increase in CR which is one of the ingredients in achieving 54 mpg.

 

I haven't seen a technology walk to get from 35 to 54, the obvious thing that'll happen is that large non luxury cars will go all electric, large luxury cars will just pay the fine, and the fleet will downsize. 

[Magoo]

If a large state like California decides to keep the higher mpg standards (which, IIRC, they can do independently from the feds, and have said they would do), doesn't that effectively become a national standard?

 

 

Depends, not necessarily. Over the years, California has often imposed stricter emissions standards than the federal government. The automakers usually responded by marketing vehicles with two different emissions systems, 49 State and California. As the manufacturers' expertise improved, they were able to make their 49 state cars meet the CA regs as well. And meanwhile, the federal and state regs converged, and also, five or six states piggybacked on the CA standards, which essentially enforced a single standard as you suggest. There are a lot of ways it could turn out, and It wouldn't be at all surprising to see two different models again. 

[Greg Locock]

Of course it is heresy to say this, but if the EPA was serious about CO2/fuel use, they'd bring light trucks and derivatives (ie body on frame SUVs) into the fold as well.

[Kelpiecross]

What we need is more tetraethyl lead.

[Lee Nicolle]

The title of this thread is,

"higher octane fuels to get to 54 mpg."

Guys and girls, we are dreaming.  Higher octane fuels will almost never allow us to get to the 2025 CAFE standard.

 

The standard of today is 35.5 mpg.  54 mpg is an increase of 52.1% over today's reality.

 

The effect of change of octane number is tightly controlled by our knowledge of the Otto Cycle which has been fully understood by the basic Laws of Thermodynamics.

 

Increases in octane numbers by themselves do not improve fuel efficiency 100 octane fuel in your car which has been optimised to burn 90 octane will make no difference other than if your car has variable timing sensors in which case you will see fuel use improvements of about 8%.

 

The real value of high octane fuels is that they allow compression ratios to be increased.  The effect of increasing compression ratios can be estimated from formulas developed from the thermodynamic characteristics of fuel compression and burning with well known boundaries.

 

I have not tried to calculate the average compression ratio of vehicles today but it is certainly above 10 to 1.  A lot of cars list values above 11 to 1 and high performance motor cycles are in the 12.5 to 1 range.

 

The articles quoted in the opening messages of this thread speak of 15 to 1 CR being possible or likely. For this discussion I will accept that estimate.

 

The important piece of science that comes from this is that raising compression ratios from 10 to 1 to 15 to 1 only provided a combustion efficiency improvement of some 13%; certainly a long way from the 52% required.  If today's average CR is closer to  11 to 1 then the efficiency improvement to 15 to 1 is only 8.3%.

 

Reaching the required CAFE in less than 10 years is going to take an enormous change to the technology mix of our vehicles which really should be the subject of a re-titled thread.

As an sometime engine builder no roadgoing engine is going to run @15-1. 100 octane Avgas is at very best 13-1 and far safer at 12-1. And 100 octane is actually higher octane than 100 anyway.  Sprintcar engines are softening the comp a bit as they got too unreliable at 15-1 and a bit! And they are designed to run wide open on alcohol. And that will never be a 'normal' fuel. It is cancerous, and gives many a headache at least, as it seems so does E85 ethanol.

Running a tightly controlled engine @ 12-1 may be possible but will be VERY critical on fuel quality, very good ignition will be required to actually burn it but even with the electronic nannys it will destroy itself fairly quickly on crap fuel. And that happens way too often, and unleaded really has a shelf life of about 60 days.

I recently bought a petrol powered pressure washer and gen set. [ I have power in those blackouts!] and both have warnings not to leave the fuel  sitting for more than 30 days. Had the same warnings on fuel system components. Who also say tanks must be kept full to minimise the problems.

[gruntguru]

Lee there are lots of cars already in the showroom running more than 12:1.

 

Toyota 86 runs 12.5: IIRC.

[Charlieman]

What is a higher octane fuel? Precise definitions are always difficult. Back in the 1950s, the FIA declared that F1 cars would race on pump petrol rather than a dope mix. The FIA were quickly advised that there was no such thing as standard pump petrol, which varied significantly between countries even when sold under the same brand. Thus F1 adopted Avgas as standard fuel for a few years, then leaded four star -- which worked more or less until the turbo 1.5 litre cars raced. F1 fuel manufacturers and engine developers concocted brews which appeared like four star when tested but weren't really petrol.

 

When unleaded fuel was adopted in Europe, engine efficiency took a knock (pun intended). European and Japanese manufacturers had increased compression ratios for family cars since the 1960s (1960s commercial vehicles often used two star leaded) and many cars were designed to run on four star, most on three star. To run on unleaded -- assuming suitable valves and seats -- some needed an octane booster. Briefly, compression ratios were reduced to work with "first generation" unleaded. Technology moved on and common sense was applied. Fuel manufacturers created higher octane unleaded petrol and car manufacturers added ECUs and sensors which accommodated different fuel standards.

 

In the UK, we now have standard unleaded and super unleaded (5-10% more expensive?) from the big brands. There was a huge kerfuffle about poor quality fuel a few years ago -- without evidence, but it sold a few replacement exhaust systems. From memory, commonly available petrol is 93 to 98 on RON scale. It is similar in Europe -- nobody complains anymore about petrol encountered on holiday.

 

The rest of the world? Have a look at the range of octane values for pump petrol available in different countries. Like in the 1950s, there is no such thing as standard pump petrol.

[Magoo]

Of course it is heresy to say this, but if the EPA was serious about CO2/fuel use, they'd bring light trucks and derivatives (ie body on frame SUVs) into the fold as well.

 

 

Totally agree that all actual passenger vehicles should be included as such in the fleet harmonic mean, but there were practical limits to the EPA's administrative powers. And as it stands now, the EPA is effectively gutted. 

[Kelpiecross]

No matter what you do %54 would need a very small and light car. Atkinson engines and variable valve timing to reduce pumping losses would help a lot. Higher octane fuel would allow the Atkinson principle to be pushed a lot further.

[Magoo]

http://www.cnbc.com/...-standards.html

[bigleagueslider]

Totally agree that all actual passenger vehicles should be included as such in the fleet harmonic mean, but there were practical limits to the EPA's administrative powers. And as it stands now, the EPA is effectively gutted. 

The EPA and NHTSA have no Constitutional authority to create federal laws on their own. Both these federal agencies are part of the federal executive, and are under the authority of the US President, who happens to be Donald Trump. President Trump has the authority to rescind any regulations issued by either agency that were not approved by Congress.

[Magoo]

The EPA and NHTSA have no Constitutional authority to create federal laws on their own. Both these federal agencies are part of the federal executive, and are under the authority of the US President, who happens to be Donald Trump. President Trump has the authority to rescind any regulations issued by either agency that were not approved by Congress.

 

 

No kidding. So now we have a president who consults not with engineers and scientists on matters affecting the environment but with televangelists and talk radio hosts. 

[Lee Nicolle]

Lee there are lots of cars already in the showroom running more than 12:1.

 

Toyota 86 runs 12.5: IIRC.

So they must run on 98 which costs 20c a litre plus more than 91. And is frequently garbage to make things worse. I have had real dramas in the past running 98. Drive into a retail petrol outlet with a car running fine, 2k down the road it is pinging its head off. This on a classic carby car primarily set up for moderate performance and good driveability and at least some economy. 

The electronic nannys will in part mask this but 12-1 in the best designed engine [basically the 86 is turbo engine with no turbo] is still at major risk on crap fuel. And 98 is far from available in many rural areas.

[Lee Nicolle]

As an aside,, I watched some You Tube vids last night with a Tesla owner. With one the battery went flat in 4 days at the airport and it had to be towed back to electricity.

And the other [same chap] who drove from central US via Vegas to LA. The trip took just about double the time. Recharging and having to drive at 3/4 of the speed limit to get to electricity. 

And with all these Tesla recharging points who is paying for the electricity? It would appear the taxpayer.

When in England I saw a recharge point with different plugs. It seems that they cannot even have a single standard with that!

And yes, again who is paying!

[gruntguru]

I believe Tesla pays for the supercharger facilities and the renewable energy supplied.

 

I agree that recharging connections should be standardised - typical "free market" lunacy. However - this is not an argument for not going electric. Last time I bought petrol, there were different bowsers for 91, 95, 98, E10, E85, Diesel and LPG (thats 7).

[Kelpiecross]

I believe Tesla pays for the supercharger facilities and the renewable energy supplied.
 
I agree that recharging connections should be standardised - typical "free market" lunacy. However - this is not an argument for not going electric. Last time I bought petrol, there were different bowsers for 91, 95, 98, E10, E85, Diesel and LPG (thats 7).

Your argument using the different liquid fuels as an example is silly.

[Greg Locock]

Interesting how few of those choices aren't driven by politics - LPG is  a government plaything (not a bad fuel for cars, but not especially sensible either, and as for ethanol, spit.)

[gruntguru]

Your argument using the different liquid fuels as an example is silly.

In what way?

[Bloggsworth]

Mazda have, apparently, cracked it with a spark-plug-less petrol engine. Incidentally, my 1.4L Petrol Skoda Octavia, cruising at about 70MPH, did 51.4MPG for the 420 mile trip from London to Scotland yesterday, so 54 MPG shouldn't be impossible.

[Greg Locock]

I'm renting a focus ecoboost, it is averaging 48.6mpUKg . It has a manual box and auto stop start. Easy way to get more mpg is to fit worse tires and put it on a diet. It seems to have hpas!

[Lee Nicolle]

Mazda have, apparently, cracked it with a spark-plug-less petrol engine. Incidentally, my 1.4L Petrol Skoda Octavia, cruising at about 70MPH, did 51.4MPG for the 420 mile trip from London to Scotland yesterday, so 54 MPG shouldn't be impossible.

You need a Kia diesel, I got 55 and change with one on that same road.

[Lee Nicolle]

Interesting how few of those choices aren't driven by politics - LPG is  a government plaything (not a bad fuel for cars, but not especially sensible either, and as for ethanol, spit.)

LPG,,,  or barby fuel is disapearing rapidly. Most new sites being built do not have it. A little scarey for someone with a factory LPG vehicle. And with unleaded at around a dollar at the bottom of the cycle and gas around 80c unviable anyway.

LPG needs to be around 40% of the price of petrol to be viable for the extra cost of conversion or vehicle cost and the 20-50% less mileage available.

As for ethanol I tend to agree but 100 octane ethanol blend is what I run my Ford Galaxie on as it goes well and no pinging. Though the whole fuel system is a bit more vulnerable.

[Alloyd]

Mazda have, apparently, cracked it with a spark-plug-less petrol engine. Incidentally, my 1.4L Petrol Skoda Octavia, cruising at about 70MPH, did 51.4MPG for the 420 mile trip from London to Scotland yesterday, so 54 MPG shouldn't be impossible.

On a similar journey my Golf regularly reports 56 to 60 mpg the southwards leg is usually worse. When I calibrate the odometer against the sat nav and do tank full to tank full at the same pump I get 50 mpg. Optimistic software. And that's UK gallons. So 40 mpUSg. On my winter tyres I get 1 to 2 mpg better. To my mind 51 mpUSg looks a long way off.