"....cars in years to come..."
Not good enough!
I want my car with frikkin' lasers on it NOW!
Spark plugs in petrol engines are set to be replaced by laser ignition systems, following development of new manufacturing techniques by Japanese boffins. The new research is to be presented to the world at an optics conference in Baltimore next month by Takunori Taira of Japan's National Institutes of Natural Sciences and his …
Diesel and petrol are taxed at the same rate as each other in the UK, diesel is more expensive because there is much higher demand for diesel (think >1/2 of all cars, and all vans & lorries) than petrol, and a given barrel of oil produces more petrol than diesel (without additional expensive refinery gubbins thrown at it). The UK currently exports petrol, and imports diesel.
/flames for fuel, not for you :)
There is another factor too, as to the price difference.
Diesel is (nowadays) much more polluting than petrol. The levels of PM10's and PM2.5's created by diesel engines are huge - even with particulate filters in the exhaust. The PM's are [mainly] hydrocarbons made of Benzine rings (a known carconagen).
Hence the EU decided (in the clean air/pollution laws) that because of the pollution created by diesels, the tax levied should be higher [than petrol]. Alas, only the UK abides to this (other EU countries ignore the law because diesels are much more popular on the continent than in the UK).
If you follow the history of diesel vs petrol prices, you will note that after the EU laws kicked in at the turn of the century (2001 to be precise, and coincided with VED - Road Tax - changes), diesel cost has overtaken petrol.
You suggest that all molecules which are derived from Benzene, e.g. Phenol, Toluene/Methylbenzene, TCP are carcinogenic, but only Benzene, with no additional molecular sub-group, is carcinogenic as far as I know. It's like saying oygen and water are very similar because they both have oxygen atoms present?
Does any of this matter, as long as you've burned the stuff and you aren't standing in a sealed garage running the engine for twelve hours (granted, the CO will get you long before trace unburned aromatics or aromatic partial combustion products)? I fail to see the evil, unless somebody is sneaking spoonfuls of polycyclic aromatics into boxes of breakfast cereal.
In most of continental Europe, diesel is still markedly cheaper, up to 10..15%, than petrol. The price difference is decreasing, though.
(glass of milk, rather, which is cheaper still per litre. Engines don't run that well on it, unfortunately)
My point being that Diesel was cheaper than Petrol, and the cost differential made it popular. This woke the sleeping pig (qv chancellor - he who kills the goose that lays the golden eggs) who increased the tax on Diesel to match.
The increased demand then led to a price rise, making it dearer still than petrol.
Flames for the rosy glow of a warm trough...
Diesel and petrol do indeed attract the same level of Duty. The reason that diesel used to be cheaper than petrol was because the duty was lower than that on petrol. I've been told two reasons for this. The more credible version was that diesel duty was lower than petrol because it was mostly used by the transport industry and therefore the industry got a tax break, as diesel cars became more common the treasury realised that they were losing out on potential revenue and equalized the duty. The less credible reason was that diesel was thought to be less harmful to the environment than petrol and the duty was raised when it was realized that diesel exhaust was every bit as nasty as petrol exhaust.
I don't buy the latter for the simple reason that the disparity in duty dated to long before governments used green issues to justify fuel duty.
It's stupid (utterly, completely pig-headedly stupid) to tax a fuel by volume, or to compare distance-per-volume. Diesel is a denser fuel. One liter contains more carbon (hence more CO2 when burned) and more energy (hence better mpg for cars of similar weight and power).
Fuel should be taxed as energy, so the tax per volume on diesel *should* be considerably higher than on petrol per unit volume. Not equal, definitely not less! This would allow motorists to select the best vehicle for their needs, on a taxation system that doesn't discriminate.
Diesels have a small thermodynamic efficiency advantage because of the higher compression ratio. This is more significant for big engines (HGVs) than for small ones (cars). Therefore for the best use of our crude oil imports, the majority of cars should use petrol. We can't do all-diesel: an oil refinery creates both petrol and diesel and has limited ability to adjust the proportions.
BTW I drive a diesel. The distorted tax system made that make sense. In a sane world I'd have chosen petrol (quieter engine, less pollution, with sane tax a lower running cost, after the expensive fully-synth oil and shorter service intervals that a diesel needs is allowed for).
Also BTW - there's a trade in refined petroleum products across the Atlantic, driven by this same tax anomaly. USA car drivers hate diesels (low winter temperatures may have something to do with it). So we ship surplus petrol to the USA, and they ship their surplus diesel back.
is driven mostly because of how long dirty diesel engines have been used in vehicles here. The popular perception is that you get billowing clouds of black smoke whenever a diesel accelerates away from a traffic light. Cold temps do have some affect of course, but the public perception is the larger issue.
As to the laser ignition system, I think it is intriguing if for no other reason than it should be a part less prone to wearing out. The potential efficiency increases are just the cherry on top.
Here's my source. http://www.petrolprices.com/why-diesel-costs-more-than-petrol.html
Similarly in Ireland, businesses are allowed to claim back the 100% of the VAT on diesel but nothing for normal petrol while in Portugal, the amounts are 50% for diesel and 0% for petrol.
BTW .. Diesels don't need spark plugs... My mum used this once before when she got charged for points and plugs on a service once in Cork many years back . She let the guy go on explaining in a slightly patronising customer service way explaining the bill, and casually dropped that in at the end... She fecking LOVED it.!!!!MWahahahah!
Sorry to be a killjoy - but how much energy does it take to ignite with a laser (versus the energy for the electrical spark), and how much does the laser mounting cost (sparkplugs being dirt cheap).
This does sound pretty awesome, but I'd like to know whether it's something that is actually worth doing this year, or whether it's on the distant horizon.
Petrol and diesel are two different fractions of the same barrel of oil. There is some overlap, and they have different additives. How much you get of each is a matter of the grade of oil, the complexity of the refining process, and the relative market prices. Europe uses more diesel then petrol, the US uses far more petrol. In Western Europe, which costs more at the pump is entirely decided by the tax man. In Turkey petrol is far more expensive.
Unfortunately, the best oil grades for diesel included Libyan oil. That has caused a massive headache for European refiners, and almost stopped me buying a diesel car. Any technology that improves petrol efficiency is to be welcomed, on energy security as well as environmental grounds. Unfortunately the technology will come too late to prevent the end of the oil age.
Saudi Arabia promised to make up any shortfall in Libyan oil from their spare capacity. However, far from increasing production by 1.6 million barrels per day, they have cut it, by 0.8 million barrels/day. Because the world is 'oversupplied' with oil. At $124/barrel.
Production is finally collapsing at Ghawar, the largest oilfield in the world. Saudi Arabia is running short of oil.
The price of oil will continue to rise until global demand is choked off. In 2008 most of the demand destruction was in the USA. Where will it fall this time?
Current multivalve heads already have the spark plug electrodes in a central position (the combustion chamber is very small at the time the spark fires, no not much protrusion is needed). Alfa Romeo have had twin sparks for decades.
The biggest advantages of lasers here are going to be more accurate timing, although electronic ignition is already way better than points and a distributor, and the lack of the heat sink effect from a big metal spark plug.
I don't think this is going to boost efficiency very much; in reality, petrol is closing the gap on diesel somewhat with the elimination of the throttle butterfly, improved compression ratios permitted by direct injection (cools the cylinder and reduces the chances of detonation) and a combination of small displacement and turbocharging, as in the latest VW engines. Diesel used to get 40% better mpg then petrol for an equivalent output engine and now it's more like 25%. Actually, when you allow for diesel fuel containing about 10% more energy per litre, the gap is already fairly small - but road fuel is sold in litres, not kilograms, so you get more MJ for your money from a diesel pump.
What should stop you buying a diesel car is the very high price of replacing the DPF and /or the dual mass flywheel, which are almost guaranteed to need replacing during the lifetime of the car, making it much more expensive to maintain than a petrol equivalent, and costing more to run over the lifetime of the car, taking in to the higher cost of diesel and the better fuel economy.
The dual mass flywheels are a nightmare! A neighbour of mine is a delivery driver (white van man) and he's had countless flywheels and clutches replaced. It kills the starter motor too.
When he spoke to Ford they said "It's not designed for start stop journeys"...
It's a bl**dy van!
I'll think I'll be sticking with my '96 oil burner for a while, certainly until they get over this idea of dual mass flywheels, or fix it!
On the diesel upside, the good old fashioned ones like mine last forever. Mine is approaching 200K. Servicing consists of little more than filter and oil changes.
And I can run it on old chip oil.
The reliability of diesels started going down hill when they began all this high pressure common rail fuel injection and all that gubbins onto them. Far too much stuff to go wrong.
As the old adage says, K.I.S.S.
Just like to say that: everything you just stated is complete and utter balls.
Why do you think all London Taxis have been diesel since the day they got rid of the horses, its because its the cheapest way to run any car. Likewise for smaller trucks and vans, with the massive torque making them the only reliable engine for larger vehicles.
The typical diesel car engine will cost less to maintain and work longer than any petrol engine. This is mostly due to the engines being built stronger to start with and the much lower rev's required to use them putting less strain on components.
Plus there are no Spark plugs and pesky HT Leads the break down.
at the last bean counting session, the total cost of ownership of a diesel car over a petrol car only becomes more cost effective after the car has done over 230,000 miles (for the average family saloon).
London "black" cabs have diesel engines for two reasons. The car is pretty much "over engineered" so that it will do close to a million miles in its life time. the extra weight of this means the extra torque of a diesel engine will come in handy.
Back when the black cab was designed, the prices of diesel was so low that it made economic sense to install a diesel power plant in a car that is going to spend 20 out of 24 hours on the road.
Also, the government encouraged people to buy diesel cars not too many years ago,,, bleating on about the lower cost, more mpg more environmentaly friendly etc... then as soon as the number of diesel cars on the road rose to significant levels, they increased duty !! bastards !!
I have owned several diesels, and various members of my family have owned lots of them for many years and I've never heard of a DPF failure.
However we all almost exclusively own VAG cars, so I don't know if that makes any difference.
My current car ('03 Golf PD Tdi) has done nearly 150,000miles and still runs like new - show me a petrol car that can claim the same.
Servicing Diesels is more expensive - granted, but even if you take into account the rediculous disparity in cost between petrol & diesel at the pump, the vastly higher efficiency still makes them far cheaper to run in the long run (so long as you do enough miles)
Although the plug is on the central axis of the cylinder in a 4-valve engine, it is at the very boundary of the fuel/air charge. This means the flame front can only propagate out in a hemisphere. If you can get the ignition point into the very centre of the charge (or better yet, two points within the charge with good spacing) then you get a bigger flame front and get a quicker overall controlled burn with less chance of detonation.
This really will make quite a big difference especially on DI engines using stratified charge - enough to compete with diseasel even on a volume-of-fuel-per-mile basis. Add the much nicer exhaust emissions of delicious petrol into the equation and this is a winner!
Wonder if I can retrofit this to a morris minor...
When the spark is required, the piston is nearest the head of the cylinder, so the volume of the area to be ignited is small. Hence the 3D centre of the volume at that point can be reached by the spark plug. However, taking time as the 4th dimension, as the piston goes down, the flame front will have further to go on the piston side than the head side. I'm not sure how a laser would improve that.
On the other hand, although spark plugs are quite light, here's hoping solid state lasers can be lighter and more easily controlled.
Anyway, I've read of ignitions that use a single-electrode spark plug with a matching protrusion on the piston dome, effectively putting the spark "inside" the fuel-air mixture instead of having it partly shielded by the ground electrode. There are also the triple- and quad-electrode plugs with the ground electrodes sideways respective to the central electrode, and surface-spark plugs, which attempt to achieve the same.
not only of the lasers themselves (although I imagine that they could quite easily be made very reliable, at a price) but of the optical conditions between laser and combustion point.
The inside of a combustion chamber isn't known for being optically pristine, and I can imagine that other engine problems (bad fuel? blown head gasket?) requiring a full set of new lasers for ££££ instead of a set of new plugs for £.
Perhaps if the fuel/air mixture is really lean it will burn clean enough not to deposit by products on the laser aperture. The other possibility is using a YAG laser means that the point of ignition is a point in space away from the exit window (YAG are groovy in that they allow you to focus a large percentage of their energy on a small point at a given distance) meaning that deposits won't affect the laser output too much, in the same way that (some) CD laser(s) can read data through a moderate amount of crud as the focal point is beyond the crud. Or maybe they will be fitted with little wipers to clean the windows :-)
I believe that the lean mixture will be required for the lasers to remain clean. The leaner you get an engine to burn, the less "crud" you get build up in the engine. The more air you have in there the more oxygen you have to react with the elements that would become "crud".
Crud = C (carbon, black solid)
Crud+air = CO2 (carbon dioxide, Oooh, a gas... Pump it out the back!)
Yes, I know, there are loads more elements in the fuel, but most will become gaseous at those temperatures when oxidised, although it might be a good idea to avoid allowing silicon to get in the fuel...
There are many transparent materials around that would laugh at the conditions in a combustion chamber. Deposit on the lens could be an issue I'll grant, but removing 'em at the annual service and cleaning the optical bit (a quick zap in the ultrasonic bath should do the job) wouldn't be too onerous a task.
I suspect that they'll turn out to be rather more reliable than direct fuel injectors as there are no moving parts and the delicate bits will be insulated from the nasty stuff by a solid lens.
My concerns are the issue of reliability given the generally dirty-ish inside of a combustion chamber where one might expect a fair proportion of the energy is lost in the window's surface after some time.
Of course, then the cost of the laser assembly.
And the opportunity for idiots to play with them outside of the engine.
Finally, I thought one problem with leaner burning engines was high NOx products? Can anyone knowledgeable comment on that aspect?
"The NOx comes mostly from incomplete combustion, which of course occurs more often with lean fuel. The idea is that the laser will be able to make the lean mix burn more completely. The end result is more boom and less NOx, basically."
That seems a bit counterintuitive. I'm not a combustion expert by any means, but it seems that a lean fuel mixture would mean more complete combustion, thus less crud. Shouldn't more oxidiser and less fuel mean thoroughly burned fuel and excess oxidiser?
I've always been taught that once you get much leaner than something like 17:1 afr two things happen. Firstly the burn becomes less efficient and secondly the burn temperature goes up (not just the required spark temperature). The upshot being that you're not getting as much energy from your fuel as you would were the mixture richer and that you're not just talking about burning your plug electrodes, but other things in the combustion chamber, favourites probably being the exhaust valves. Then you end up having to use things like sodium cooled exhaust valves to stop them getting burned.
Also I would have thought that the optimum afr was the one where there was exaclty the right amount of oxygen to burn the amount of fuel you had. Too little oxygen and you're getting unburned fuel coming out of the exhaust, to much oxygen and you're wasting energy compressing gas that isn't getting used. Actually that latter point always interested me because you're always wasting energy compressing a whole load of nitrogen that isn't getting used. If you could run your car on petrol and pure oxygen you would be running more efficiently because you wouldn't be wasting energy compressing all that pointless nitrogen.
So there are two reasons a leaner mixture will produce less power per stroke than a richer one, firstly you're burning less fuel and secondly you're wasting your output power compressing unnecessary gas.
If you want to burn less fuel use a smaller engine or possibly lower revs.
Stochiometry - 14.7:1 air:fuel - is primarily needed because it's the only point at which catalytic converters are efficient. If it wasn't, then running leaner would give better economy, running richer better power. But - for closed-loop three-way precious-metal cats, 14.7:1 or Lambda 1.0 is king.
Pity, really. Ricardo had 21:1 lean-burn running properly back in the early '90s, before cats were forced on us, helped immensely by the precious metals lobby. The drawback with that tech, though, was high NOx levels - and that's become more and more of an issue in recent years.
So... How, exactly, will firing the mixture via raygun solve that issue? After all, it's not the spark plug that's currently restricting the mixture, but the emissions and legislation.
I would think that what they want to do is make the mixture much leaner as the engine speeds up into the upper rev range. You get more energy out of a richer mixture, but it may well burn more slowly.
Leaner mixtures burn hotter because they burn faster.
Engines get desperately inefficient at the top end of the rev range and the timings required to get it right become impossibly critical. This laser idea stands to improve the burn timing accuracy and efficiency at the top end of the rev range. If they can get this to work reliably and for a reasonable cost I can see potentially great gains from it.
The leaner the AFR, the higher the combustion temperature and the propensity to form NOx emissions - which are the bug-bear of diesel engines.
Now (cooled) EGR (Exhaust Gas Recirculation) can be used to reduce the effective displacement of the cylinder, substituting "dead air" having reduced O2 content for fresh air, so that NOx are less likely to be produced because there's more distance between available oxygen molecules and because the extra amount of "inert" gases requires more energy to heat up. Lean-running engines will always produce more NOx than those running stoichiometrically or rich. Modern diesel engines are meeting a similar challenge.
NOx may be accummulated in a "catalyst" and when that's "full", sensed by NOx emissions post-catalyst rising, the engine management system causes the engine to run rich for a while, which provides for the release of the NOx and conversion via catalyst to N2 and O2 (as well as water and CO2).
Spark-ignition engines solve the problem of igniting an overall-lean mixture by stratified charging; varying the rate of fuel delivery so that an easily-ignitable mixture is around the electrode(s) when the time comes. This is a "doddle" with diIrect injection.
“Timing – quick combustion – is very important," should not be mis-interpreted. The idea is not to burn the fuel as rapidly as possible but to provide reliable ignition timing. An explosive burn would destroy an engine in minutes. The high-speed gas flow would strip the protective boundary layer of gases from metal surfaces, exposing them directly to temperatures that'll burn through the metal very quickly. (This is what happens during severe knock; a condition that is exascerbated by highcombustion temperatures.)
The efficiency of an engine is best measured the old way, how much fuel it takes to produce so much power for so long. Pints per horsepower hour is the way we used to do it. Probably Kg per KWHour or something these days. Simply running leaner does not imply greater efficiency.
Lets say a particular car needs 30hp to drive it down the road at 70mph. So to drive 70 miles at 70mph will take 30hp hours. Running leaner will not necessarilly mean it uses less fuel to do that work. It may be that running leaner means you need more throttle to achieve your 70mph - the upshot of which being of course you're using more fuel air mixture to produce the same power. That in turn could mean that you are using exactly the same amount of fuel as you were before, or if could mean you are using more.
This reminds me of the stories about the magic carb that was killed off by the petrol companies. If you've never heard the tale, there was a story going round years ago that a carburettor was invented that would allow cars to run a lot leaner and hence use a lot less fuel, but produce as much power. However, the conspiracy theorists behind this tale believe that although this carburettor existed and was patented the petrol companies bought it up and stopped is being sold. Presumably they also managed to disappear the patent since no such patent exists. The stupid thing about this little story is that almost any carb can be set up to run leaner, but that will just mean that your fuel air mixture is too weak for the rest of your engine. The carbs (or these days the fuel injections) job is just to mix fuel and air, it's the engine itself that determines how well that is burned. However the myth still has a certain staying power and some continue to believe it. To those people I say get hold of a mappable ECU for any modern car and change the maps to make it run leaner and see what that does for you.
The real advantages I see from this tech are (1) that you would no longer need to replace your plugs. Having said that plug life is getting longer and longer anyway. I remember having to swap plugs every six thousand miles. My current car needs new plugs only one tenth as often. Cheaper servicing would obviously result. and (2) if something went wrong you wouldn't end up foulling your plugs with excess fuel or other crud and your car would have more chance of starting in that situation.
"If you could run your car on petrol and pure oxygen you would be running more efficiently because you wouldn't be wasting energy compressing all that pointless nitrogen."
Doing this would certainly give you big bang followed by total silence unles you were running a gas turbine.
Laser igniters will probably end up as SFP modules that can be plugged into the space a spark plug used to occupy. It also remains to be seen whether they will become like CD player lasers that are so cheap they can be thrown into any CE device. How long will I have to wait to plug one into my 3.5 hp push Alba lawn mower? The spark plug has to be cleaned once or twice a year.
(Yes, it is an Alba lawn mower. That's not the brand on the box, but the manual says the brand is owned by that venerable maker of cheap hi-fi kit and I since reading that I've never been able to remember the name of the brand)
Some while ago, Honda used CVCC (compound vortex controlled combustion) engines to run leaner without exotic sparking tech.
Pretty easy; you have two fuel circuits. Each cylinder has another little tiny cylinder, with no piston, next to it. Lean mix goes in the main cylinder. Rich mix goes in the little one. Spark plug fires up the rich mix, which then spills into the main cylinder, igniting the lean mix therein. Result: Car runs leaner overall without the problems you normally get from that, fuel efficiency goes way up.
It's a mature technology--my 1977 Honda Civic had it. Works very well, and another nice side effect is that it runs a whole lot cleaner, too. They used 'em for quite a while, through the late 80s at least and I think even into the 90s. Always wondered why that tech didn't catch on in a wider way.
1. The London taxi was designed with a petrol engine in mind and first produced with such (the 2.2 IOE smoke dispenser from the Landrover if I remember correctly, it certainly didnt dispense much power, I do know that). It took several models and in fact more than 2 manufacturers of Taxis before they came with the currently ubiquitous (and battlefield-smoke-screen enhanced) diesel that the majority of the FX4s still bumbling around are fitted with. Theyre easy to tell apart - one pukes out blue smoke, and the other pukes out soot like a extra from Mary Poppins. To be fair theres not so many of the Petrol FX4s about nowadays and they're all being gradually replaced by new models.
2. Diesel is more efficient than petrol, true. Diesel is generally more reliable than petrol, also true, but ignore filters and the like at your peril with a diesel - anyone who has seen a compression ignition engine decide to eat its own lubrication oil and 'runaway' can attest to what an unpleasant and costly experience that is. Diesel however is heavier, slower revving and positively anemic at high revs. I also dont suggest being anywhere near a turbocharged/supercharged diesel if some idiot decides - rev limiter, whats one of thems then.... not to mention getting petrol-style high performance out of them is like getting honesty out of a politicians expenses.
3. Lasers and piston crowns - I dont like where this is going - I can see a badly adjusted or incorrectly spec'ced laser igniter chewing its way through a piston crown and munching engines in short order - I could almost predict a Ro80 style - 'count how many engines I have detonated by the number of fingers I hold up' owners greeting on early cars fitted with this.
4. Why hasn't anyone gone down the pressure scavenged two stroke route for modern cars - Chrysler almost did it with a two stroke Neon (they had a test mule running) - plus you get twice the power for a given displacement/tune - eg 2.2 Renault 12v douvrin engine - 136 to 272hp and thats not to add on the gains from a proper tuned pipe exhaust (another thing that Chrysler did waaaaaaay back in the 1950s, although they tuned the intakes). What a wonderful idea, a car the size of the Mundane-o with a 1100, 250+hp engine..
Its all very well orgasming at the next idea to come out of Toyota or the like - or some think tank, but when you consider *why* we still use spark plugs and coil/coil(s) and the like, its very simple - it works, its generally reliable and its cheap and cost effective...
more to the point just how long do you think it would take someone with a skull emptier than a chavs Brain-pan - to take one of the things out of a junked car, get a small 12v battery and go round blinding old people with it, cos they wont let him down the youff club - ASBO's are such a pain in the behind sometimes...
Oh yeah, and the wonderful hybrids -
Humber Sceptre - 1964 - 6 speed transmission - 100mph+ - 35mpg (with aerodynamics like a barn door with an obesity problem) - price now £2500
Toyota Prius - 2011 - CVT (constantly vacuous transmission) - 99mph - 42-44mpg - not to mention all the pollution regarding the battery systems and transport before the thing even moves... £25000 plus however much it costs to replace the battery when it finally coughs.
Its been calculated that if you ran something like the Sceptre from delivery new to now, doing an average mileage, driving reasonably and keeping everything tuned and in trim... you'd produce less pollution in 55 years, than is created just in manufacturing and transporting a Toyota Pious to a UK forecourt (not to mention that the Prius petrol engine is a less efficient Atkinson cycle motor, for a reason I have yet to fathom).
Oh and multi valve heads - were being fitted to bugattis in the early 20's - and even cars in the Austin 7 racing series could be fitted with a multi valve head. Not to mention the Dolomite Sprint and all sorts of different machinery - its not a new concept. Pretty much nothing is. Oddly enough Ettore Bugatti left behind designs for a 22cc supercharged cycle-motor engine, that would fit, complete, into the palm of your hand, and put out a good 3-4 projected horsepower. thats 1hp per 6cc or the equivalent of 1000hp in a 6 litre engine... suck on that Veyron...
There is little point adding more and more complication for complications sake. Oooh look, I can buy a Focus that can park itself, wonderful idea, until you fail your test because you actually have to be able to DRIVE!
If you're running lean there's more oxygen to combine so combustion should be more complete. Most NoX emissions are a result of the higher temperatures involved (this is why aircooled engines are usually run rich - richer == cooler)
Lean burn has been banned in the USA for years (there's legislation forcing stoichiometric mixtures) because of NoX emissions and they jump on it a lot harder than on this side of the pond.
Utilising lean burn allows petrol engines to get very high mileage figures, so it's a pity there hasn't been enough research in this area in the last 20 years thanks to USA legistlators.
Still, there are a huge number of areas where efficiencies can be increased.
Dumping belt-driven accessories and substituting an exhaust-gas-driven alternator would help for starters (GM experimented with THAT in the 1930s, so there's plenty of prior art and no patents to have to deal with). On a similar note A/Cs can be driven from hot exhaust gases - https://secure.wikimedia.org/wikipedia/en/wiki/Absorption_refrigerator
You get NOx, Nitrogen Oxides, by burning the Nitrogen in air. This happens when you have a lean, high temperature combustion. If it's not lean, there is no excess Oxygen to combine with Nitrogen. If it's not hot, you can't burn. Lean means excess Oxygen, Rich means excess fuel.
To limit NOx emission, modern engines burn a bit richer, and are a bit less efficient. So there is hydrocarbon polution in the exhaust. That's what the catalytic converter is for.
The catalytic converter gets rid of the excess fuel in the exhaust, which is there because the engine burns rich to reduce NOx.
In fact, an old, pre-pollution control, engine is more efficient than a modern efficient engine, because those engines burned leaner. And it wasn't particularly limited by spark plug design. Those old cars were less efficient, but that was because they had 3-speed gearboxes. Which is a different story.
It may be that the spark plug is a limiting factor in pollution control, and an evener burn may let them make the overall mixture leaner. Certainly designing a cylinder to get an even burn is difficult, and pollution comes from hot spots and cold spots in the flame front.
By the way, modern distilleries use high temperature "cracking" with catalysts to "crack" long-chain hydrocarbons (crude oil) into lighter fragments (octane, pentane, "petroleum"). The fractions that you get depend on the secret cracking recipe, not just on what you get out of the ground. So if the US is swapping diesel for petroleum, it's a complex economic and technical marketplace, not because they are pumping diesel out ot the ground
First, for whatever reason, diesel here costs more than gasoline for some reason. People are dumb, and don't realize a diesel will get so much higher MPG as to dwarf the small price difference.
Second, gasoline here is relatively cheap (it's approaching $4 a gallon), and traditionally people here have not given a toss as much about MPG. It's fun now to poke fun at people that bought some horribly inefficient SUV or something a year or two ago, WHILE everyone was telling them gas prices would spike, and now they are bitching about gas prices being so high*.
Third, the big push for diesels here was in the late 70s. Everything then ran horribly. But, we ended up with stuff like VW Diesel Rabbits, and GM made a few horrible diesels where they just took a gas V8 or V6 and upped the compression. They all barely could move, and smoked like crazy. People here think of this and of busses and semis (the local busses were VERY smokey until just a year or two ago, I think the city and University may have gotten new diesel mechanics.)
Fourth factor now, EMISSIONS. VW has sold TDIs here for years, which are fabulous, but even had to pull those off the market for a few years because they couldn't meet emissions. We don't have quite the same standards for gas and diesel engines but diesel emissions aren't so lax as in other countrys.
*On a side tangent -- we can finally get decent-MPG cars here within the last year or so, with more coming out as 2012 models. US'ians don't all want gas guzzlers, there was almost no choice in the matter. From the early 1990s to like 2011, if I had wanted a good-MPG vehicle, there was basically Geo Metro (before it went off the market in the mid-90s), Prius, a few years of the Honda Insight (before it also ballooned into the non-efficient vehicle they sell now), and various VW TDI models. THAT'S IT. Before the last year or so, there was this absurd feedback loop running for years. It went like this: Car companies looked at sales figures, they saw people with the cash buying larger cars, and cars with more power. Conclusion? For years, the larger vehicles and V6s have been tuned for mileage (tall cruising gears and whatever MPG-improving tricks they can put on), they'll get like 28-30MPG highway, and the few V8s will do at least 25MPG. Smaller vehicles? They'll take a model that gets good MPG everywhere else, decide it needs more power to have a chance to sell -- result, they lower the gearing, they soup up the engine at expense of MPG or entirely replace the engine with a US-specific one. They are sold at a low price so fuel-saving technologies may not be fitted to them. So you end up with a subcompact car that gets 30-32MPG highway. Which would you buy, a subcompact that gets 30MPG, or a larger, more powerful vehicle that ALSO gets 30MPG? They then looked at sales figures, rinse and repeat. FINALLY within the last year or so there's more 35-40+MPG models coming out, and not surprisingly they are selling great.
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