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Why you should consider a diesel as your next car

A brief history of diesel

Before I tell you why you should consider the diesel for your next car, it is perhaps instructive to know why and how the diesel engine came to be.

Toward the end of the 19th century, the world was looking for a more efficient and compact alternative to steam engines, which had already been in used for over a hundred years. The steam engine had made the Industrial Revolution possible, but it was inefficient, bulky, and tiresome to operate.

The answer was the internal combustion engine, with diesel-powered engines being one alternative, and petrol-powered engines being the other. Diesel engines eventually won favor over petrol engines for a number of reasons, but mainly because they were considerably more efficient and safer.

Steam engines like the one here were bulky, inefficient, and required many people to operate. (Image source: Tortured Mind Photography)
Steam engines like the one here were bulky, inefficient, and required many people to operate. (Image source: Tortured Mind Photography)

Early steam and petrol engines were only about 10% to 15% efficient, but diesel engines trumped them by being over 30% efficient. In fact, modern two-stroke diesel engines, such as the ones found on large container ships today, can be as much as 50% efficient. Furthermore, in the early days of internal combustion engines, leaks were not uncommon, and diesel had the advantage because diesel fuel was less flammable and would not ignite even with an open flame, unlike petrol. This made diesel engines safer.

A couple of people could lay claim to being the inventor of the diesel engine, but the man widely regarded to be the father of the modern day diesel engine is Rudolf Diesel, a German inventor and mechanical engineer. In his research, he found that air, if compressed heavily enough, would get so warm that it would ignite diesel fuel. This is the basis of the diesel engine.

German inventor and mechanical engineer Rudolf Diesel is widely regarded as the founding father of diesel engines. (Image source: Wikipedia)
German inventor and mechanical engineer Rudolf Diesel is widely regarded as the founding father of diesel engines. (Image source: Wikipedia)

Today, diesel-powered engines are quite literally the beating heart of modern civilization. The taxis and buses that transport people around cities are powered almost exclusively by diesel engines; the ships that carry goods around the world are powered by diesel engines; the jeeps, trucks and tanks that form the backbone of the world’s militaries are all powered by diesel engines too.

How are diesel and petrol engines different?

The diesel and petrol engines that are used in most cars are highly similar. In essence, they are internal combustion engines that work using a two or four-stroke cycle. In an internal combustion engine, the power cycle is made up of four phases: intake, compression, power and exhaust.

In the intake phase, air is drawn into cylinder through the opening intake valve. In the compression phase, the intake valve closes and air is compressed with fuel. At this point, the mixture of fuel and air is ignited to cause an explosion. It is this explosion that causes the piston to downwards and drive the crankshaft to produce motion. This is the power phase. The final phase is exhaust where the spent air-fuel mixture is expelled out of the cylinder through the opening exhaust valve so that a new cycle may begin.

Petrol and diesel engines operate using the same principle, but the difference lies in the spark plug. Diesel engines don't have any.
Petrol and diesel engines operate using the same principle, but the difference lies in the spark plug. Diesel engines don't have any.

The main difference between diesel and petrol engines is that petrol engines use spark plugs to ignite the air-fuel mixture, while diesel engines rely solely on heavily compressed air. As mentioned earlier, Rudolf Diesel found that the temperature of air could be made to increase high enough if it was heavily compressed. The temperature would rise so high to the point where it could cause the ignition of diesel fuel.

Therefore in diesel engines, air in cylinder would be very heavily compressed, typically to around 14 to 23 times its original volume. In petrol engines, the compression ratio is generally much lower, because they rely more on the spark plug to begin the power phase. The compression ratio is petrol engines is typically around only around 7 to 10, with high performance vehicles having higher compression ratios of up to 13.

A graph showing the relationship of thermal efficiency and compression ratios. Efficiency continues to increase significantly from compression ratios of 10 to 20. (Image source: Duke Engines)
A graph showing the relationship of thermal efficiency and compression ratios. Efficiency continues to increase significantly from compression ratios of 10 to 20. (Image source: Duke Engines)

High compression ratios are desirable because it results in higher thermal efficiency. In other words, more energy can be extracted out of the air-fuel mixture. This also explains why diesel engines are considerably more efficient than petrol engines. In fact, diesel engines have the highest thermal efficiency of any internal combustion engine.

The Pros and Cons

Besides being very efficient, what other advantages do diesel engines have over their petrol counterparts? And what disadvantages do diesel engines have? Let’s take a look at some of the important ones briefly here.

Pros

  • Not only are diesel engines more efficient, diesel fuel is also cheaper to purchase. At the time of writing, diesel fuel is around 40% cheaper per liter than petrol. This means diesel vehicles will be cheaper to run, which also explains why buses and most taxis have diesel engines.

  • Because diesel engines are so efficient, cars can get incredible mileage out of them. It is not uncommon for passengers cars with modest 50 liter fuel tanks to be able to travel over 1000km on a single tank. This means more time spent traveling and less time spent refueling.

  • To withstand the high compression of gases within the cylinders, diesel engines are built to be extremely hardy and will generally last longer than their petrol counterparts. They can also go longer between maintenance.

  • Diesel engines can be made to run on alternative and renewable fuels like biodiesel with little or no modifications. Biodiesel generally refers to used vegetable oil that has been used for cooking, and is then recycled and treated so that it can be used to power diesel cars.

Cons

  • Diesel engines need to be built stronger to withstand the high compression of gases, as a result, they usually cost more to manufacture. Consequently, diesel cars can sometimes cost more than their petrol equivalent. This depends heavily on the manufacturer.

  • Diesel engines produce a distinctive knocking sound that is referred to as diesel clatter. This sound is the result of the sudden ignition of fuel which causes a pressure wave. It makes diesel engines sound less refined and noisier.

  • Diesel engines are heavier and less eager to rev than petrol engines, which makes them undesirable in sports cars. This also makes diesel powered cars less peppy and engaging to drive.

  • In Singapore, diesel cars are subjected to a special tax on top of the typical road tax which can add to the running costs of the car. Since this tax can be substantial, we will address it in greater detail below.

Special Tax

Diesel cars used to be a rarity in Singapore, and that’s not surprising considering the bad reputation it has had. Diesel cars are often considered to be polluting and slow, and it didn’t help that a huge special tax was levied on diesel cars. This special tax is placed on diesel cars because there’s no duty on diesel fuel. Petrol, on the other hand, are subjected to a petrol duty which, according to the LTA, encourages fuel conservation and discourages excessive use of petrol cars that may contribute to congestion and pollution.

But times have changed dramatically in the past decade. Diesel technology has improved rapidly, and governments are recognizing the environmental benefits that diesel cars have and have put legislations in place to promote their sales. As a result, sales of diesel cars have been on the rise. In many European countries, such as Austria, Belgium and Germany, sales of diesel cars are on a par with or have even surpassed that of petrol cars.

In Singapore, petrol passenger cars greatly outnumber diesel ones. But diesels are becoming more popular amongst more savvy car owners lately.
In Singapore, petrol passenger cars greatly outnumber diesel ones. But diesels are becoming more popular amongst more savvy car owners lately.

In Singapore, sales of diesel cars are on the rise, albeit slowly. Knowledgeable car buyers are now open to trying out diesel and that has been helped in part by the government, who has revised the special tax on diesel cars. For modern diesel cars which meet the Euro V standards, the special tax has been drastically reduced. To get a sense of how much cheaper it is to drive a diesel car now, one only has to look at the tax rates.

For a pre-Euro IV compliant car, the special tax is a whopping 6 times the road tax of the petrol equivalent. In other words, if we take a 1600cc diesel car as an example which has a 6-month base road tax of S$372, the special tax levied on a pre-Euro IV compliant diesel car would be a whopping S$2,232. The total 6-month tax would therefore be S$2,604.

For a Euro IV compliant car, the special tax is calculated to be $0.625 per cc of engine capacity and subjected to a minimum of S$625. This means that on top of the 6-month base road tax of S$372, we have to add a special tax of S$1000. Hence, the total road tax would be S$1,372 for 6 months. It’s substantially less, but it’s still a significant markup over a petrol equivalent car.

However, if you got a new diesel which is Euro V or JPN2009 compliant, the special tax is calculated at a lower rate of $0.20 per cc and subjected to a minimum of $200. This means that for a 1600cc diesel, the special tax levied would be just S$320, bringing the total 6 month road tax to a much more reasonable and affordable S$692.

Here's a table to recap the various tax payable using a car with a 1600cc engine as a comparion.

Car Type

Total tax

S$2,604

S$1,372

S$692

S$372

This meant that in the past and with older diesel cars, you’d have to cover huge distances to be able to justify the additional costs of the special tax. But thanks to the more favorable tax rates, it is now more affordable and financially practical to drive a diesel.

Note: This article was first published on 24th July 2016.

A Day with the BMW 216d Gran Tourer

So we now know that diesel cars are more advanced and efficient, plus they are also more affordable to own and drive. But what is it like to actually drive one? For that, we turn to the BMW 216d Gran Tourer - one of the more recent diesel cars to be launched in Singapore.

The 216d Gran Tourer might be a 2 Series, but it ain't a coupe or convertible. (Image source: BMW Asia)
The 216d Gran Tourer might be a 2 Series, but it ain't a coupe or convertible. (Image source: BMW Asia)

To begin, the BMW 216d Gran Tourer is a bit of an oddball because it lies nestled deep in BMW’s 2 Series lineup. The 2 Series is actually home to BMW’s sporty rear-wheel coupe and convertibles. However, the 216d Gran Tourer is a family oriented front-wheel drive MPV that will comfortably seat seven - drastically different from the other models in the 2 Series family.

The “d” in its name denotes that it is a diesel-powered car and the 216d Gran Tourer is in fact powered by a very economical 1.5-liter 3-cylinder turbocharged diesel engine. Fuel consumption is rated at 4.4l/100km or roughly 22.7km/l, which is pretty impressive. Carbon emissions is judged to be 116g per kilometer, which puts it in the second lowest bracket in the CEVS (Carbon Emissions-based Vehicle Scheme) and qualifies the 216d Gran Tourer for a $15,000 rebate (at least until the newer VES scheme takes over).

Don’t be put off by its tiny sounding diesel engine. Despite its small size, it still serves up 116hp and a very generous 270nm of torque, that’s enough to propel it from 0 to 100km/h in 10.9 seconds, which is very respectable for a 7-seater MPV. I found it to be quick enough for our roads and had sufficient poke to ensure that overtaking cars and changing cars was never a problem.

But perhaps more importantly, the little 3-cylinder engine feels very refined. Sure, there’s some noticeable diesel clatter upon start-up and idle, but once it gets going, it revs quite freely and is also very quiet.

Besides being fuel efficient, the 216d Gran Tourer is also very practical. With the third row of seats folded, the boot become cavernous. (Image source: BMW Asia)
Besides being fuel efficient, the 216d Gran Tourer is also very practical. With the third row of seats folded, the boot become cavernous. (Image source: BMW Asia)

And as you would expect, it’s really fuel efficient. I’m a pretty heavy-footed driver, but in my experience with the car and with a good mix of urban and highway driving, I managed a fuel economy reading of about 17km/l or just about 5.8l/100km. If you find yourselves cruising on the highways more often or if you have a light foot, you can expect to get even better numbers.

In short, I was really impressed with the BMW 216d Gran Tourer and how far modern diesel cars have come. There’s little difference in terms of refinement, and the diesel clatter that many have come to associate with diesel cars is only apparent if you are listening out for it. There’s plenty of performance here too. In fact, for the most part of my time with the car, I wasn’t even aware that I was driving a diesel at all. And that’s high praise for any diesel car.

Final Thoughts

Forget all the stereotypes diesels that you know about diesels. Modern diesels are remarkably refined vehicles that are quiet, smooth to drive, and offer credible performance. My guess is that in a blind test, only enthusiasts will be able to tell the difference between a petrol and a diesel car. And to top it all off, diesel cars have amazing fuel efficiency.

Diesels are offered by just about every carmaker these days. Even Maserati's new Ghibli has a diesel option. (Image source: Maserati)
Diesels are offered by just about every carmaker these days. Even Maserati's new Ghibli has a diesel option. (Image source: Maserati)

But before you run off to your nearest dealer, there are some things to consider. First of all, there’s the special tax that I mentioned earlier. That’s the most acute cost consideration for potential buyers. Although it has been reduced significantly, it still represents a large recurring cost that will affect your total ownership costs.

The good thing, however, is that the low prices of diesel fuel will eventually pay off this special tax. But this would obviously require diesel car owners to travel a substantial amount each year.

Some other considerations include maintenance costs. By and large, diesel cars are just as reliable as petrol cars and regular servicing costs are roughly the same. But an important thing to note is that certain components that are exclusive to diesel cars, can be costly to replace. For example, a component called the diesel particulate filter which is used to remove soot from exhaust gases, is known to be pricey to replace. Fortunately, these things don’t break down easily and shouldn’t be a problem if the vehicle has been properly maintained and used.

Euro V diesel was only recently introduced in Malaysia, so finding a station that stocks it can be difficult. If you head up north frequently, that's something to consider.
Euro V diesel was only recently introduced in Malaysia, so finding a station that stocks it can be difficult. If you head up north frequently, that's something to consider.

Readers that frequently head north to Malaysia should also take heed. Unlike Singapore petrol stations, which all stock Euro V compliant diesel fuel, most of Malaysia’s petrol stations only supply lower grade Euro 2M diesel. This lower grade of diesel has a higher sulphur content which is unsuitable for modern diesel engines. Using Euro 2M diesel in a Euro 5 compliant car could clog the car’s diesel particulate filter and may cost engine damage, which will be costly to repair.

Fortunately, given that diesel cars can quite easily cover in excess of 1000km on a single tank - enough for a trip to Genting Highlands and back - only the most transient drivers would need to fill up in Malaysia. For owners who do find themselves with an empty tank in Malaysia, it is recommended that they only fill up what’s required to get them back to Singapore.

All things considered, diesel cars should certainly be considered by readers who have the need to travel extensively around Singapore. Though the special tax can be off-putting, the cost savings of cheaper diesel fuel and the added fuel efficiency should make it pay off in the long run.