What is the difference between diesel and petrol cars?

In today's context, how does the debate about diesel and gasoline engines stack up?

Back in the days when a beard meant you were the kind of guy who loved to commune with nature by crushing it in a big heavy SUV, life was simple and we all knew whether we wanted a diesel, a smoking blunderbuss or a gas. -a squishy machine that felt at home on smooth roads or in cities.

Today, when a beard can simply mean that you live in Melbourne and think your trousers should be spray-painted, things are much less clear.

Gasoline cars are still high-revving, savory jobs that consume a little more but are more fun to do so, and you can still get a diesel 4WD to take you past the back of Bourque, but you'll also find plenty of diesels. in city cars, from the Volkswagen Polos, through the Mazda 6 and all the way to the luxury barges of the BMW 7 Series. And you'll find sports cars parked at your local diesel tanker, which is now right in the middle of the gas stations instead of off to the side where the trucks fill up.

Diesel has changed; it went mainstream and spread its oily wings to many corners of the automotive market.

You can even get a diesel-powered Porsche, for God's sake, although, characteristically, not under the hood of a 911, Cayman, or Boxster.

Diesel has changed; it has gone mainstream and has spread its buttery little wings in many corners of the automotive market, offering better fuel economy (about a third better) and longer intervals between fill-ups, making the offer all the more enticing.

We are far from the European level of diesel consumption, where for some brands diesel is the dominant engine in their fleets (for now, but rule changes in some countries will change this soon), but its acceptance has grown significantly. The number of diesels on our roads has jumped noticeably over the past five years. In the UK, however, diesel sales have recently fallen by almost 40 per cent as a ban on this type of engine in that country becomes more likely.

So, in today's context, how does the diesel vs. petrol debate stack up?

Gasoline or diesel? Driven by their differences

All you, as a driver, really need to know is that diesel and petrol vehicles deliver their power or grunt differently. 

Gasoline engines are all about revs, and they tend to hit their peak power - or funny moment - at more revs. They deliver the excitement of the wind upwards; as the revs rise and you change gears, the speed increases. This makes them more colorful and exciting, at least in theory.

Diesel engines give out their grumbling - in the form of torque (or torque, as it's sometimes called, which is more descriptive; it's the type of power that can propel you up a steep hill, even with weight on board) - at much lower rpm.

Diesels are great for cruising, especially on the highway, because overtaking power is always on point, often without even having to downshift.

The differences are huge and noticeable: the diesel engine puts out three times as much power at a point just above idle. So from 1500 rpm to 3000 rpm you get an instant boost. However, they are more like a draft horse than a racehorse, because if you push them to a higher rev range, the grunt will die down.

This means diesels are great for cruising, especially on the highway, because overtaking power is always on point, often without even having to downshift. They are also great for towing things.

In tight corners on a windy road or on a race track, they offer a very different experience from a petrol car, but they can still be fun and even competitive, like Audi's success in the diesel-powered 24 Hours of Le Mans. engines proves.

Part of this success, of course, is based on the ability of a diesel car to go further on one tank of fuel, but more on that later.

The scientific and oily part of why diesel is different is combustion; the point at which fuel mixes with air. In a diesel engine, liquid is supplied to the combustion chamber under pressure, and combustion occurs instantly.

Diesel engines don't even need spark plugs like gasoline engines do. They mix air and fuel outside the combustion chamber at the intake port.

Another advantage of diesel is that it has a much higher compression ratio than unleaded gasoline, making it more efficient.

Economic argument

A big part of comparing a diesel engine to a gasoline engine is fuel efficiency. Diesels are simply better in this regard, 30 or even 40 percent better, although modern direct-injection gasoline engines are catching up.

This not only saves you money (although the slightly higher price of diesel should be taken into account), but it also saves you time because you get more range from the tank - more than 1000 km in some cars - and that means fewer car service visits. service station.

Diesels have become even more efficient and less wasteful over the last decade or so, thanks to the addition of high-tech electronic injectors and common-rail systems to ensure accurate diesel delivery and less nasty soot.

Diesels are more expensive than gasoline-powered cars, and this fact has to be taken into account when it comes to the money you save on your fuel bills.

These improvements also made it possible for diesels to sound less like rattling old asthmatic tractors and more like cars, although you would still never call them an exciting engine sound. Modern cars are focused on hiding diesel sounds from inside the cabin, and they do an excellent job of that.

Diesel supercars, however, are as common as Donald Trump's humble moments.

Another economic factor, of course, is that diesel vehicles are more expensive than gasoline vehicles, and this fact has to be taken into account when it comes to the money you save on your fuel bills.

How much more can vary, but 10-15 percent is a reasonable number.

Car companies will claim that it's because they don't make as many of them, so they have to charge more, or that it's because their engines have more heavy parts or are more complex, that everything costs more. (This complexity could also mean higher maintenance costs and theoretically shorter engine life.)

Frankly, all these arguments are quite plausible, and in other markets you may well find a different approach to pricing.

The surcharge now also means you get a little more when you sell the car, because when we look at the resale value of petrol and diesel cars, the Australian market gives the impression that diesels are worth more.

People tend to do the math by calculating how many miles you need to drive before you get back the extra money you spent on fuel economy, but it's probably not going to be the deciding factor after all. .

Let's say you opted for a Mazda6 or Hyundai i30 because they are perfect for your lifestyle, you love their style and they fit within your budget. The extra 10 percent can pay off after a while if you don't ride long distances, but in the end it's best to ride both and decide which one you like better.

Unless you really, really hate the service station, then you will take diesel every time.

Gasoline or diesel? It's a personal thing

In the end, it is impossible to say which is better, petrol or diesel engines, because it depends on the specific case or from car to car, and also depends on personal preference.

Some people just can't stand the sound diesel engines make, especially under load, so they'll never buy one. While the best European brands, especially the high end ones, now make diesel engines that are so quiet you can barely tell which engine you're driving without rolling your windows.

If you are going to regularly tow a boat or motorhome, this is not a problem, because a diesel will do the job better and use much less fuel.

Diesels also tend to rattle and cough more when you use the start/stop system, which can be annoying, but again, car companies are starting to get to grips with this issue. Even Peugeot now makes nearly flawless start/stop diesel engines.

Part of it is what you want to do with your car. If you are going to regularly tow a boat or motorhome, this is not a problem, because a diesel will do the job better and use much less fuel.

If you want a sports car and the thrill of a high-revving engine, you need gasoline. That's why, as good as Mazda's diesels are, they don't put them in the MX-5 roadster. It just won't feel or sound right.

However, in a small commuter car like the i30 or a mid-sized family car like the Mazda6, the diesel actually feels better to drive. This low torque is an absolute boon for small engines and is much more comfortable and enjoyable in everyday work. Add in the savings figures and it fully justifies the extra cost.

Target emissions

One thing you have to consider, of course, is diesel emissions, which the recent Volkswagen scandal has shown us to be a big problem.

Some cities, such as London and Paris, where the mayor has said she wants all diesel cars off the roads by 2020, are now passing laws to ban all diesel cars due to the levels of nitrogen dioxide they emit. produce.

(Parts of London have banned both petrol and diesel vehicles since the end of this year to improve air quality, so it's not just oil burners.)

The World Health Organization estimates that nitrogen dioxide causes more than 22,000 deaths in Europe every year.

Exposure to nitrogen dioxide can cause lung and heart disease, as well as asthma, allergies, and other airborne infections. It has also been linked to Sudden Infant Death Syndrome, miscarriage, and birth defects.

The World Health Organization estimates that nitrogen dioxide causes more than 22,000 deaths each year in Europe, where roughly half of all cars are diesel (but that number is declining, and in the UK it has dropped to 32 percent and continues to decline).

Australians currently burn almost three billion liters of diesel per year in cars alone, with another 9.5 billion liters used in commercial vehicles, and it is estimated that about 80 per cent of nitrogen dioxide pollution in our cities comes from cars, trucks, buses and buses. bicycles.

On a positive note, Australia's air is among the cleanest in the developed world, and yet air pollution kills more than 3000 Australians a year, nearly three times as many as in car accidents.

However, it is worth bearing in mind that Australia may one day, and this may happen in a few decades, following more enlightened and more polluted countries like Europe, introduce some kind of ban on diesel fuel. 

Do you prefer diesel or petrol vehicles? Tell us what you think in the comments below.