By Derryn Wong

IT’S BEEN A bumper week for greenie-motorists with the launch of two alternative propulsion vehicles right here in Singapore. ‘Alternative propulsion’ refers to vehicles, which use anything other than gasoline to power their forward motion.

The first one out is Audi’s A5 coupe, debuted on June 16. While already launched last year with petrol engines, it’s now available with a 3.0-litre turbocharged diesel engine, which marks the first diesel passenger car offered here from Audi.

The second is more familiar – it’s the newest, third-generation Toyota Prius was launched on June 19 by local Toyota dealers Borneo Motors. As the car of choice for environmentally-conscious Hollywood celebrities and with more than a million units sold globally, it needs little introduction.

How important these vehicles are for each brand respectively goes far beyond mere sales figures – they are also vital building blocks to brand perception by the public. With both cars touting high efficiency and (in the Audi’s case) high-performance, we’ve decided to go the whole hog and bring you up to speed on the state of alternative propulsion here and the hard facts behind buying one.

And while common perceptions might suggest that hybrids are the default choice for someone who wants to get the most out of their fuel tank, as well as minimising their carbon footprint, the facts are quite surprising.

DIESEL (TDI): How it works

Aren’t diesel engines smoky and for tractors? Not TDI ones anyway.

There’s a good reason why 60 percent of all Audis are TDIs, and more than half of all passenger cars sold in Western Europe are diesels. It’s because modern diesel engines are proven to be fuel efficient, powerful and clean.

TDI stands for Turbocharged Direct Injection, which refers to the technology used by Audi (and the greater Volkswagen Group) in its modern range of diesel cars.

All diesel engines work on the basic concept of compression – that is they use the ‘squashing’ motion of the piston in the cylinder to auto-ignite without the use of a spark plug, like gasoline engines require.

This makes them more thermally efficient than petrol engines i.e. less energy is converted to heat and more to movement. Diesel engines have higher compression than gasoline ones, which means more fuel molecules (diesel also contains more energy than gas) are squeezed and more of it is converted to energy.

Turbocharging adds even more efficiency by further compression. TDI engines also use piezo-electric injectors for maximum efficiency and quietness. The last part of the system is the diesel particulate filter/catalyser, which removes a great quantity of pollutants and greenhouse gases.

Audi A5 3.0 TDI: what’s new

As you can see from the spec charts, the only difference between the regular petrol A5 and the TDI version is the 3.0-litre, 240bhp turbodiesel engine under the hood. But the effect it has is pretty impressive: despite having less overall power, it’s faster to the 100km/h mark thanks to the massive torque, a highlight of most diesel engines.

Not only does it make 170Nm more, it does so lower in the rev range at 1,500rpm which in everyday driving is almost instantaneous. It also fulfils the promises of better fuel consumption and reduced emissions.

Real life:

Pros

1. Enjoy less fuel bills
In the case of the A5, the 3.0-litre TDI engine gives 33 percent better combined fuel economy over the 3.2-litre gasoline version.

2. Enjoy more driving fun
As explained, more torque means more kick-in-the-rear shove for instant overtaking at any speeds. Overall power is lower, but the massive torque explains why the TDI is quicker to 100km/h. Bigger horsepower equates generally to higher top speed which is less applicable in real life and even more so here when the cars are electronically limited at top whack.

3. Green credentials
182g/km of CO2 might not seem like a big improvement, but in the class of luxury, two-door four-seat sports cars it is an impressive figure. A BMW 335i coupe emits 232g/km while a Lexus GS 450h hybrid luxury saloon for produces 180g/km of CO2. While it might take some time for the rest of the world to catch on, driving a modern diesel still lets you have fun.

Cons

1. The dreaded diesel tax
If diesels are so great, why isn’t everybody driving one? They already are – in Europe, where diesel prices are often equal to or more than prevailing gas prices. Singapore however, has the special (i.e. outdated) diesel tax – an additional $0.625 per cc, at a minimum of $625 per half a year. Thus the A5 TDI will cost you a whopping $6,078 per annum in road tax. (see next page for analysis)

2. Clean diesels need good fuel
Modern diesel engines work well because they run on modern fuel with less sulphur content and impurities – this is even more true of bio or synthetically-derived diesel, which will become more widespread in the future. In Singapore we get high-grade diesel, so this is not a problem, but using low-grade fuel overseas is bad for the engine.