What's more environmentally friendly a petrol or diesel engined car?

Question

I am lucky enough to be able to buy a brand new car soon. What is the least damaging to the environment petrol or diesel?

Answer 1

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 center 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.

Answer 2

Its not clear-cut.

It may depend on the environment you live in, and the type of driving you do - but a normal petrol car is usually not an environmentally friendly option.

The environmentally friendly options are:
Diesel
CNG
LPG
Hybrid
E85 / Ethanol.

If you live in a city, or any other area, that suffers from a build-up of particulates, then you should avoid a diesel unless fitted with a particulate filter. Your best bet here will probably be E85, CNG or LPG as these have low carbon content and burn cleanly - see which fuel is available locally.

However, the inherent efficiency of a diesel engine means it produces less CO2 than the spark ignition engine used by all the other options, despite the diesel fuel's higher carbon content.

If you do mostly stop-start town driving, a hybrid is likely to be the most environmentally friendly, provided you can adapt your driving style to make the most of the regenerative braking (where instead of turning your kinetic energy into heat, it turns it into electricity, stored in batteries, which is then used to get you moving again).

If you do mostly motorway driving, or other reasonably steady-speed driving, you don't get any advantage from a hybrid, so diesel is the best bet due to its efficient engine.

The E85 or Ethanol option is a trickier one to work out. In theory the CO2 produced by burning the ethanol has been captured by growing the plants used to produce the fuel, so is not additional carbon in the atmosphere. However in real life the production of ethanol isn't quite that efficient, and there is no definitive answer at present to how environmentally friendly it really is.

The big advantage of petrol and diesel are the availability of the fuel - there's no point buying an E85 compatible car if you have to drive 40 (polluting) miles to get to the E85 filling station.

However, if you don't do many miles, you need to consider the environmental effect of producing the car and getting it to you, not the environmental effect of using it. In this case, you should choose the simplest, most locally produced car - in the UK this is probably a base-spec petrol-engined Nissan Micra (A Toyota Aygo would be a very good choice if you lived closer to the factory in the Czech Republic).

I did warn you it wasn't clear cut.

Answer 3

The answer is that the diesel is the more ecologically friendly. That would only apply to a very modern diesel engine, but as you are buying brand-new, then that is understood.

Diesel gives more miles per gallon, all modern diesels have catalysers to knock-out harmful NOX emissions, and all will have very effective particulate filters. Diesel engine management is also very effective in ensuring that the engine runs in the most efficient way possible at all times.

Buy a Japanese car with a diesel engine, and you can't go wrong. The new Honda diesel is a superb piece of engineering, and light-years away from the smokey old knock-boxes of the past.

Answer 4

Diesel gives off less Co2 than petrol, but petrol gives out little else, wheras diesel has a concoction of odours and visible gases that it also gives off. While much of this can now be filtered, they still are there. If you want to be kind to the environment though don't worry about all this crap of giving off less emissions, plant 6 trees in your garden and they will breathe in all the Co2 given off by a 4.0 V8 car engine, running continously and a little bit more. This idea of turning the gases back into oxygen never gets mentioned by companies or the government as there is no money in it. (oh and i'm not some tree-hugging Hippie, just find them funny!!)

Answer 5

Whoa... no offence but there's a lot of bull in the answers here.

Petrol generates a higher CO2 output than diesel. But diesel is equally bad for the environment because of the particulates it releases (these are specifically thought to have been responsible for the increase in asthma in children in the West Midlands).

Sadly the alternate fuels don't quite offer a decent alternative yet - electric vehicles still have minimal range, and LPG etc is potentially quite dangerous (they're not allowed in the channel tunnel nor multi storey car parks in many European countries). There are hybrids out there - eg cars with both battery fuel cell and petrol capability but they're limited and prohibitively expensive. If that doesn't' worry you check out Toyota, Lexus and Honda.

If you really want to reduce your environmental footprint and your life dictates that you must have a car, go for one with a small engine and use it as little as possible.

Answer 6

Washington is really a huge and all know city and is certainly suitable deliver a vacation or just visit this city. with hotelbye you'll learn more. One of the icons of Washington and the whole America could be the popular White House, the state house of the President of the United States. The home of each president except George Washington, it had been initially built by James Hoban in 1792, and following being burned down by British forces in 1814 was rebuilt in 1818. Even though travels of the interior including the East, Blue, Green, and Red Rooms; the Ballroom; and the State Dining Room should be reserved properly ahead of time, every tourist to Washington may wish to see this legendary developing, at the least from the outside. Nearby to the White House would be the elaborate 1833 Greek Revival Treasury Building and the 1871 Executive Office Building, one of the very most impressive old government buildings in Washington.

Answer 7

In January 2007, the EPA finally set new smog rules for diesels. The auto industry was waiting for that to happen, and now they're introducing a bunch of clean, faster engines. Diesels emit different types of pollutant. Gas engines tend to emit CO and HC. Diesels tend to emit SO2, NOx, and particulate. Gas engines use catalysts to eliminate CO and HC, but lead would destroy the catalysts, which is why there is unleaded gasoline. As of 2007, new diesels use catalysts to eliminate NOx and particulate, but sulfur would destroy the catalysts, so there'll be low-sulfur diesel. That eliminates SO2. But the #1 reason diesels are better is that any diesel can run biodiesel, which is an efficient, practical biofuel. Ethanol is NOT efficient or practical, it takes too much energy to distill it. Hybrid diesels make a lot of sense. I expect to see them in the next generation of plug-in hybrids.

Answer 8

A diesel emits less CO2, but more particulates, as opposed to petrol, and have better fuel economy.

As for hybrids, most of them are too impractical or expensive for many, and the Toyota Prius isn't as economical as some diesels.

Answer 9

Diesel is said to be better as it goes for longer on one gallon / litre. Diesel itself is dirtier but new cars are much better. However if you REALLY want to protect the environment either:
1. buy the smalled car you can live with and use it minimally.
2. go for a hybrid car like a Prias

Answer 10

LPG and Hybrid are more enviromentally friendly than both!

Usually diesel is a bit more economical but petrol is greener (That's why there are more taxes on Diesel)

Answer 11

diesel is dirtier, but petrol is less economic, so in the long run you let out more fumes. Its a close call, go for which ever is cheapest as there reli isnt much difference