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  #1  
Old 09-18-2003, 12:53 PM
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Diesel emissions-the truth

Found this over at http://www.dieseltruckresource.com:

The truth about diesel emissions

Forget about all those smoky old buses and trucks, the truth is that the modern diesel car is as clean, and probably cleaner than an equivalent petrol car. Don't believe me? - read on.

The five main emissions for petrol and diesel cars are:-

Carbon Dioxide (CO2)

Carbon Monoxide (CO)

Nitrogen Oxides (NOx)

Hydrocarbons

Particulates

Of these five, a diesel car is better than a petrol car with three of them, about the same with one, and worse with one. Only one of these classes of emissions is visible (particulates, or soot), and rather unfortunately for diesel cars, that is the one which is worse for them. The three emissions for which petrol cars are worse are invisible, so you won't realise that they are there; however they still cause harm to health and the environment.

What problems do these emissions cause, and how does diesel stack up:-

Carbon Dioxide

Carbon dioxide is the main cause for concern at the moment, and is the subject of international agreements to try to reduce its output. Carbon dioxide is causing global warming; this is a known fact. Carbon dioxide is produced by any burning of fossil fuels, and is caused by production of electricity by most current powerstations; this means that electric cars cause carbon dioxide emissions too. Carbon dioxide does not cause any health issues.

Carbon dioxide emissions are directly proportional to fuel consumption, and as diesel cars use 30 to 40% less fuel, they emit 30 to 40% less carbon dioxide than petrol cars. Natural gas and LPG cars are actually quite fuel inefficient, if otherwise cleaner burning, and so produce more CO2 than a diesel.

Although CO2 emissions are not directly harmful to us, they are changing our climate. The legacy these emissions will leave will be felt by every generation after us.

Carbon Monoxide

Carbon monoxide is a poison. It has no smell, but can kill you without you realising what is happening. Carbon monoxide is the reason why you should not run you car engine (petrol) in a confined space. Diesel engines produce virtually no carbon monoxide, a petrol engine produces enough to kill you. The main remedy to carbon monoxide emissions of petrol engines has been the introduction of catalytic converters, however there are problems with cats:-

They don't work until they are hot, maybe 10 or 15 minutes of driving. As most car journeys only last 10 or 15 minutes, the cat is not terribly effective.

They increase fuel consumption.

They are easily poisoned and stop working.

They are easily mechanically damaged.

Nitrogen Oxides

Nitrogen is the main constituent of the air that we breathe. When it is exposed to high pressures and temperatures it combines with oxygen in the air to form nitrous oxides. The nitrous oxides then combine with low level ozone to form smog. Because of the way a diesel engine works, with an excess of air inside the engine (rather than "just enough" as in a petrol engine, which is what causes CO emissions), nitrous oxides are more likely to be formed. However tests of actual cars reveal that whilst emissions of NOx are higher in a new diesel than a new petrol car, that by 50,000 miles or so they are the same, and after that the petrol engine produces more than the diesel. Therefore over the life cycle of the car, petrol and diesel engine emissions of nitrous oxides are similar. Emissions of nitrous oxides can be effectively reduced in both petrol and diesel cars by use of exhaust gas recirculation (EGR). EGR reduces the combustion temperature to below the point where nitrogen effectively burns.

Hydrocarbons

Hydrocarbons include chemicals such as benzene. Benzene is an extremely carcinogen chemical, and has been declared unsafe by the World Health Organisation in any concentration. Hydrocarbon emissions are contained in petrol engine emissions much more than in diesel engine emissions. Benzene is also present in the fumes which can be smelt when filling up with petrol at a service station, this is not a problem with diesel.

Particulates

Particulates or smoke are really the only problem for diesels (compared with petrol engines). Most of the controversies and newspaper scare stories centre around particulates. Various groups have been trying for years to prove a link between diesel smoke and cancer, and so far have failed to actually prove anything. Friends of the Earth may come up with statements such as "Small particles are believed to lead to 8,100 premature urban deaths every year (1.9% of all deaths in urban areas)" and then apply them to diesel emissions, but this is flawed because:-

The studies were carried out in American cities where the penetration of diesel in the market is lower. Any increase in deaths due to particulates, if it exists, may be caused be particulates from some other source; the particulates in question have not been indisputably linked with diesel emissions.

Even in Europe, particulates from diesel cars are a very small percentage of the particulate emissions which we breathe; most are from industry.

Diesel engines emit more PM10 particles, that is particles which have a diameter up to 10 microns, but petrol cars actually emit more PM1 particles than diesel ones. These particles are smaller than 1 micron and are invisible. They are also more likely to penetrate deeply into human lungs (as they are smaller) and look less like a natural dust particle, which human lungs have evolved to cope with.

Even if particulates are a factor in the deaths of 8,100 people every year in the UK, then these are the most seriously unwell people in the country. The fact is that we are talking about 8,100 people who are about to die, with or without particulates around.

The original research which led to the link between deaths and particulates is being questioned. See Merlise Clyde's paper, Model Uncertainty and Health Effect Studies for Particulate Matter, which can be downloaded from The National Research Center for Statistics and the Environment in Washington.

Summary

Diesel cars are better than petrol cars with reference to carbon dioxide, the global warming gas.

Diesel cars are better than petrol cars with reference to carbon monoxide, a poison.

Diesel cars are better than petrol cars with reference to hydrocarbons which cause cancer.

Diesel cars are similar to petrol cars with reference to nitrous oxides, which cause smog.

Diesel cars are worse than petrol cars with reference to particulates, which have unproved health impacts.
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Old 09-18-2003, 01:34 PM
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Too bad we can't capture the NOx and reintroduce it into the intake system to produce more power from the engine.
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Old 09-18-2003, 02:00 PM
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Quote:
Originally posted by Hawk180
Too bad we can't capture the NOx and reintroduce it into the intake system to produce more power from the engine.
Or we could just sell it to all the guys with Hondas
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Old 09-18-2003, 02:14 PM
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In the large aircraft I work with, we have a system called the Onboard Inert Gas Generating System or OBIGGS, (Aviation is full of abbreviations). It seperates nitrogen from the surrounding air by the use of micromembranes, compresses it into storage tanks and dissipates it into the outage of the fuel tanks to inert the gasses in the tanks. If some of you engineer types could come up with a compact version of this to seperate the NOx from the exhaust gasses to pump back into the intake system, we could be onto something here.
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Old 09-18-2003, 02:46 PM
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The wrong NOx...

You all are after the wrong NOx. Nitrous oxide is N2O, and is good for providing more oxygen for combustion. The nitrogen oxides produced by our vehicles are primarily nitric oxide, NO, and nitrogen dioxide, NO2. As far as I know, putting these back into the intake system would do nothing for combustion, other than possible inhibition.
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Old 09-18-2003, 02:48 PM
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My mistake, the post did say nitrous oxide rather than nitric oxide. Hey I'm an airplane guy, not a car guy.
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Old 09-18-2003, 04:00 PM
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Not to pick a fight, but I have to challenge the allegation that global warming is a known fact. I would classify global warming as at least the result of junk science. There are serious debates on the topic. Only among the left, the main stream press and those who have accepted their view is it a "known fact".
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Old 09-18-2003, 04:22 PM
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Quote:
Originally posted by MS Fowler
Not to pick a fight, but I have to challenge the allegation that global warming is a known fact. I would classify global warming as at least the result of junk science. There are serious debates on the topic. Only among the left, the main stream press and those who have accepted their view is it a "known fact".
Yeah, they should have stated it as a "known theory".
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Old 09-18-2003, 05:49 PM
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There isn't 100% reliable evidence that global warming due to CO2 is happening, but it has been proven that average temperatures have been on the rise in the last century and that CO2 is a heat-trapping gas. So naturally it makes sense not to release too much CO2 into the atmosphere and it makes sense to drive fuel-efficient cars.

About the emissions, I'm surprised that gasoline engines emit more PM1 particulates than diesels. If that's really the case, then gasoline engines are even worse than I thought.
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Old 09-18-2003, 06:12 PM
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What about direct injection gassers? I've heard about their ultra-low emissions and high power output. If they are so great why arn't the everywhere?
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Old 09-18-2003, 08:14 PM
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Probably because the injectors take a heavy beating. I'll bet they haven't worked the bugs out yet.
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Old 09-19-2003, 11:48 AM
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Stop wasting gas and oil in power plants and go to nuclear. NO co2 emissions from nuke plants.

P E H
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Old 09-19-2003, 12:26 PM
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I'd have to concur with DieselAddict. While global temps may be rising, they are far below the warming period we had in the middle ages. I don't recall that civilization did anything to cause that warming period. Sun spot activity may in fact be the key to our temperature cycles and mankind cannot do anything to change it.

Mt. Pinatubo put more greenhouse gasses into the atmosphere than all of mankind ever did. Global temperatures were down for a couple of years then stabilized. Or so I read somewhere, I can't recall the source.
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Old 09-19-2003, 06:18 PM
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I read the same thing. One good volcanic explosion puts out more nitrous oxides than we've prevented by mandating NOX emissions.

I also find it curious that nobody talked about global warming during our unusually cold winter in Michigan the past year!
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Old 09-20-2003, 12:01 AM
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Quote:
Forget about all those smoky old buses and trucks, the truth is that the modern diesel car is as clean, and probably cleaner than an equivalent petrol car.
That's why inhaling gas fumes for too long makes you feel kind of sick, but inhaling diesel fumes makes you feel rather happy. Occassionally a truck will idle outside the air intake vents where I work... and I LIKE it. :p Way better than the cigarette smokers that like to puff there dispite all the signs NOT to.
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