Question, how can having a lower compression ratio make for better emissions? I've often wondered why this seems to be the norm for the automotive industry to build low compression engines. Am I way off base here thinking that if the air / fuel mixture is compressed more that it would not only burn cleaner but more efficiently?
Lower compression for less emissions
- Thread starter Dan the man
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I agree with you. The things the Government mandated, that automakers vehicles get better emissions & fuel economy, (starting back in the late 60s?) was & is B.S. Automakers know how to do this with-out the Government telling them HOW. They don't know near as much as the people who BUILD the vehicles. Lower compression, EGR valves & a lot of other un-necessary items on (older) cars didn't help emissions or mileage. Now a days, car & trucks have higher compression, less "emissions" junk on the engines, & make way more power than they used to. They burn cleaner than ever, & 500 h.p. vehicles are getting pretty damn good gas mileage too Technology, not the Government, is mainly responsible for this. Thanks for letting me VENT.
new engines can be 12 to 1 or higher /its all about hydrocarbon and nox's in the old days the higher compression makes more heat / the egr valve let the cooler exhaust gas into the cylinder to cool it down and it has very little o2 left in it to burn
Rat Bastid
Dunamis Metron
It didn’t. This is what happens when lawyers write laws about things for which they are wholly unqualified for.
Lower compression also increases heat in the exhaust. Makes less power. Burns more fuel per horsepower per hour (BSFC).
There is nothing good about low compression ratios.
MopaR&D
Nerd Member
The government didn't mandate HOW to reduce emissions, they just set the standards (which can still be BS but that's a different topic). In the 1970s engine designers knew far less than they do now about what goes on inside a combustion chamber. It was known at the time that NOx is produced from high combustion temps, higher compression generally gives higher temps, so reduce compression and NOx will go down. What it took them until the 80s to figure out was that you could keep the combustion temps down and accomplish a more complete combustion (less CO and HC emissions) by using a higher-compression fast-burn closed-chamber head with 'swirl' ports to induce turbulence into the intake mixture for better mixing. EGR systems also became more sophisticated to where you don't even realize they're there anymore (yes modern cars still use it). Modern engines use high compression for the efficiency benefits and have the technology (VVT, knock sensors, fast-reacting EFI and ignition systems) to keep emissions as low as ever. Not to mention catalytic converter technology has come a LONG way since the 1970s. Cars today emit 1/100 of the pollutants that late-70s cars did even with all their add-on emissions junk. And all the EPA has really been doing is making the standards stricter.
The early emissions-equipped cars of the 70s-80s ran like garbage because they were running carbs at super lean mixtures with super retarded ignition timing; EFI really was the key to getting engines to burn clean and still run the way they should because they could instantly react to changing conditions and adjust the AFR and ignition timing on-the-fly.
So to answer the OP question, with what we know today, no there is absolutely no benefit for an engine to have a low compression ratio aside from being able to run low-octane fuel. And it produces less heat in high-load-cycle applications (trucks, industrial, marine applications etc.)
The early emissions-equipped cars of the 70s-80s ran like garbage because they were running carbs at super lean mixtures with super retarded ignition timing; EFI really was the key to getting engines to burn clean and still run the way they should because they could instantly react to changing conditions and adjust the AFR and ignition timing on-the-fly.
So to answer the OP question, with what we know today, no there is absolutely no benefit for an engine to have a low compression ratio aside from being able to run low-octane fuel. And it produces less heat in high-load-cycle applications (trucks, industrial, marine applications etc.)
dano
Evil Handy Man
Its all about a homogeneous mix and flame front. It all needs to burn efficiently. That's why newer heads have "swirl" technology, better chamber designs, revised spark plug placement, more efficient ports, variable valve timing, turbos, and multiple smaller valves. CVT transmissions limit transience as its easier to maintain economy and emissions at a fixed RPM.
Electric cars will replace this all and that is happening now. Gas and Diesel engines will become less available to the point of just being used in Hybrids. Its been this way for Locomotives since 1925.
Electric cars will replace this all and that is happening now. Gas and Diesel engines will become less available to the point of just being used in Hybrids. Its been this way for Locomotives since 1925.
Says who? and why are they "better?
Rat Bastid
Dunamis Metron
You are just flat wrong. The government made up some bullshit standards to meet. And then they changed the standards. Those changes required different methods to achieve those bullshit standards.
If you think that back in the 1970’s the engineers and such at GM, Ford and Chrysler didn’t know anything about combustion you are just fooling yourselves.
Those people had to meet some ridiculous nonsense made up standards, standards made up by incompetent idiots whose only concern was to reduce the number of cars on the road and miles driven.
Corporate Average Fuel Economy (CAFE) standards are some of the most regressive regulations there are.
Swirl only matters if you want to get the cats lit off when cold. After that, it’s a power killer.
MopaR&D
Nerd Member
I didn't say they didn't know anything, I said they knew a lot less than they do now. There are actual interviews with engineers from back then who admitted their knowledge of combustion in relation to emissions was minimal. They knew that closed-chamber, high-turbulence heads produced faster and more efficient combustion. But they thought faster combustion meant higher temps meaning more NOx which is false. This is why Chrysler for example went to open-chamber heads on big blocks starting in 1968. Testing new engine designs before the advent of things like CFD and CAD was very slow and just couldn't be done quickly enough to get the best results before it was time to roll out the next models.
Also, how were the standards bullshit if they had measurable and visual effects? Big cities in the 70s were all a hazy smoggy mess, plenty of members here who grew up in L.A. for example will attest to the drastic change in air quality once emissions regulations went into effect.
I'm not saying the EPA was "right" or did things properly and didn't have ulterior motives (lobbies, corruption) in many cases but it's definitely not a black-and-white situation where any government intervention whatsoever was a mistake and ruined the auto industry. The way it was executed was heavily flawed but it was bound to happen sooner or later with how addicted Americans are to driving their personal cars everywhere instead of walking, riding bicycles or using public transportation. Obviously not talking about rural country towns but dense urban areas where air quality was so bad it was causing measurable health effects to the people living there and everyone had the attitude, why exert myself walking or riding a bike when I can jump in my comfy car and get there with no effort?
EDIT: Also how could swirl ports produce faster cat light-off if they produced faster and more complete combustion which ends up with less heat going out the exhaust? I'm pretty sure the way they did that was making the exhaust manifolds and pipes upstream of the cats more restrictive to retain heat and increase gas velocity...
dano
Evil Handy Man
I didn't say they we're better, I said they are the future. Legislation, CAFE standards, etc are dictating that as we speak. OEM's have set dates to stop or greatly limit implementing fuel based engines in new production vehicles.
Rat Bastid
Dunamis Metron
Let me say this. You don’t know that the air is any cleaner than it was 200 years ago. I say it is even with cars. Brainwashed fools who think that the industrial revolution is killing the planet are who is really killing the planet.
Geology correctly understood says the earths air was polluted in different ways in different epochs. So I don’t care what the government thinks about much because the government as a collective knows nothing.
Second, those engineers weren’t plagued with all the rules and crap that comes along today. Those engines were literally being retrofitted to comply with bullshit rules and regulations.
“Modern” chambers get way too much credit for emissions and power. Largely the results we have today are from computer controlled feeling and ignition timing. The average idiot driving down the road today is no better than the average idiot driving down the road in 1974. The difference is back then there was a required tune up interval that was virtually ignored by the vast motoring public. The computer has reduced that tune up requirement by an order of magnitude.
You want to ride a bus or bike to work move to China. You’ll be among your own.
If you think swirl is a performance modification you are just wrong again. Swirl is used to light the cats off cold AND it has some effect at relatively low air speeds in the port. For performance it’s a loser.
It gets the cats lit quicker because it helps with fuel control again at low air speeds. And, you have to handicap cam timing along with the swirl port to make it happen.
Rat Bastid
Dunamis Metron
Again, the “rules” were dropped and the engineers had to work with what they had. The government has no business telling ANY business how to make anything.
MopaR&D
Nerd Member
Again, not paying attention to what I'm saying. I'm not talking about the "earth's air", I'm talking about localized pollution in urban areas. Don't lump me in as a tree-hugging moron just because I argue for pollution control on combustion devices. It's a known fact in chemistry and biology that hydrocarbon particulates or gases, carbon monoxide and oxides of nitrogen are very bad for your health. Screw what the tree-huggers say, I learned that on my own from studying this exact subject in grad school. And I bet what you'll say next is "yeah and all those colleges are run by liberals who want to brainwash kids and blah blah blah", save it I've already heard it.
You do make a good point about the chamber design vs. more advanced controls, I will give you that. Some modern engines (mainly 4-valvers) really don't have that great of a chamber design. When I was talking about better modern chamber design I was thinking more along the lines of the G3 Hemi with the dual quench pads and dual spark plugs compared to say a G2 Hemi or SB/BB Wedge.
I didn't say anything about swirl ports being a performance improvement either. Stop putting words in my mouth. And if I want to ride a damn bus or bike to work I'll choose to because I have the freedom. Americans as a whole won't change unless they want to and government regulations sure won't do it, there needs to be a cultural shift where people choose to drive less out of their own desire to not be wasteful. Actually I think it's already happening with us "damn snowflake millenials".
Trying to talk about emissions on this forum is almost as bad as talking about a global pandemic or gas prices. Leave the political crap out of it, let's just keep it to science and tech, PLEASE.
This^^
In Edwards F Obert's work titled "Internal Combustion Engines and Air Pollution" lays it out in chapter 10.
Page 374: A number of major and minor changes in former engine and component design can reduce radically HC CO and NOx emissions.
1. The primary 2 major changes in engine design have been to reduce compression ratios from high 10+ values to more-desirable urban rations of 8 to 8.5 and sealing of crank case emissions.
With a reduction in compression ratios, combustion temperatures are reduced and exhaust residual increased (Less NOx) and exhaust temperatures increased. Less HC
There are many factors involved in being able to run much higher compression ratio's but that discussion is beyond the scope of most people here. There are 2 people that I have come across that say they can run up to 21 to 1 compression but you would need to have a deeper understanding of what they are doing and why to discuss it. Both have a very deep and specific knowledge and understanding of combustion and they also have a good grasp of the scientific literature that has been written in regards to the topic.
Hope this helps.
harrisonm
Well-Known Member
It's not really venting if it's true.
MOPAROFFICIAL
If it has tits, it's a liabilititty.
Would one be right to think a lower octane fuel would produce less hydro/nox....
Using too high an octane than the min needed for maximum efficiency burns slower making more heat...not more power.
I like the follow the money.
I notice we have some pretty good crude refining here in the USA...that we export.
Consider the region the car was manufactured for when it comes to low octane/low compression and then the above.
Using too high an octane than the min needed for maximum efficiency burns slower making more heat...not more power.
I like the follow the money.
I notice we have some pretty good crude refining here in the USA...that we export.
Consider the region the car was manufactured for when it comes to low octane/low compression and then the above.
Rat Bastid
Dunamis Metron
Combustion temperatures drop it exhaust temps go up.
1. Compression ratios are going back up. The desirable compression ratio is the most you can run on the fuel available and the limits of detonation of that fuel and the chassis/drivetrain requirements.
Once again I say that the requirements change as far as emissions are concerned. One day they are worried about one thing and the next it’s another.
And cleaning up one side of the equation can and will affect another.
Rat Bastid
Dunamis Metron
I answered that. I get that you think swirl is a power maker but it is in fact a power loser. It is for emissions only and 99% for cold start emissions. And it requires cam timing changes for it.
Ask anyone what drives the tree hugging, sandal wearing, granola eaters wild the most and it’s cold start emissions.
Rat Bastid
Dunamis Metron
I didn’t put words in your mouth. You brought up bicycles and mass transportation.
You exposed yourself. Your own words say you THINK the US needs to change. That we need to drive less. I say you have the problem.
You want me to drive less because you think it’s wasteful. Screw you. You have bought it all, hook line and sinker that man is killing the planet. And it’s not true.
I don’t care if you ride a bike. You see, I agree you have that right. Just keep it off my streets, which were designed for and paid for (mostly) by internal combustion engines. Those streets are for that use, not some fool on a bicycle.
I continue to increase my carbon foot print. I do it because I can plant a tree and do more good than all the government regulations and Greta Thunbergs the illogical world can breed.
Edit: I forgot to mention the busses you want to ride. I suspect you never do it or you wouldn’t advocate for it if you did. All forms of mass transportation are inherently inefficient. All of them. As last I looked not a single mass transit system in the US is self funding. That’s right. That means that I have to pay to subsidize something I don’t and won’t use.
You want to ride a bus I’m fine with it. Just make sure your fare pas for ALL OF IT. We’re that the case you might see how financially pathetic that system is. I won’t even consider how much money is wasted every year building rail systems, bus only lanes and stupid **** like that. None of which per dollar spent is as efficient as spending that road tax and other monies on fixing, maintaining and building new roads for cars and the commercial vehicles that deliver the food and other commodities needed for a first world country.
And yet, every year more money is dumped into those inefficient systems because it makes people like you feel better.
As a nation we’re are in retrograde. We are stumbling backwards at an alarming rate. In one more generation we could be a third world nation. That’s exactly where we are heading. Your notions only make that happen sooner.
We have already abandoned manufacturing to the point we can’t defend ourselves. We don’t have the materials to produce our own weapons systems.
I could go on, but it always comes full circle. No matter where you look at the circle, it points to retrograde thinking and behaviors.
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MOPAROFFICIAL
If it has tits, it's a liabilititty.
Most alternative energy is costly to maintain, short lived and inefficient vs the current... and as pointed out the bridge of mass transportation is thee most pollutant source of the discussion.
The problem lies with the powers to be...
..and diving further...the countries where the poor have the most children and have zero environment concern.
The problem is..
8.4 billion people... the poorest families having the most kids as a 'financial tactic' to sustain
4+ cars to a family
Entire governments using mass transport when mostly the pos is half empty and running 24-7
All the plastic cars still constantly produced
What ever happened to that concern , "the plastics are destroying the planet, boo hoo"
...meanwhile still buys iPhones, Chinese TVs, Chinese everything, still supports stupid home craft business who buy cheap ornaments by the box from china then make some marketed as "earth friendly/natural"... then they go finance a tesla or some other plastic car and drive like they own the hwy till a 410 valiant ***** slaps them back to reality...its all artificial.
Nothing is real ..as it was at one time. Its artificial...down to the smallest problems...all created...
Human problems 101..
The problem lies with the powers to be...
..and diving further...the countries where the poor have the most children and have zero environment concern.
The problem is..
8.4 billion people... the poorest families having the most kids as a 'financial tactic' to sustain
4+ cars to a family
Entire governments using mass transport when mostly the pos is half empty and running 24-7
All the plastic cars still constantly produced
What ever happened to that concern , "the plastics are destroying the planet, boo hoo"
...meanwhile still buys iPhones, Chinese TVs, Chinese everything, still supports stupid home craft business who buy cheap ornaments by the box from china then make some marketed as "earth friendly/natural"... then they go finance a tesla or some other plastic car and drive like they own the hwy till a 410 valiant ***** slaps them back to reality...its all artificial.
Nothing is real ..as it was at one time. Its artificial...down to the smallest problems...all created...
Human problems 101..
Stored kinetic energy from regenerative braking, no high voltage, no 900# batteries, no rare-earth magnets, no rediculous explosion of electricity generation & grid infrastructure. Would greatly boost city mpg easily.
Electric vehicle's are a joke, limited traveling distance. Once there's only electric vehicle's, see what your taxes do then as the government has to make up for the lost revenue from gasoline taxes. Also the charging stations at different locations cost 5k a piece that cost will be passed on to the consumer. Charging your electric car at home requires a 220 outlet how many people have those in their garage? And you can't use a extension card for it.
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