Sustaining Future

Sunday, October 29, 2006

Diesel or Petrol

Environment issues aside, do you want to own a diesel engine car or a petrol car?

Carsguide.com.au made a comparison of VW Jetta. Well the test is not a strict comparison:
We'd prefer the same transmission in each car, but it simply isn't possible. So the diesel Jetta has a six-speed manual gearbox; the FSI is available with the six-speed DSG transmission only. And the non-turbo FSI engine would have been our first choice.


We are interested in the preformance, so here is the result of Carsguide's test:
the diesel needing 9.7 seconds for the 0-100km/h sprint, the FSI petrol 9.2 seconds. The FSI Turbo DSG is a clear performance winner with a sprint of 7.2 seconds.

It's a little slower that the rest, but the diesel's flexibility comes into its own on the mid-range overtaking sprint from 80-120 km/h when it takes 8.5 seconds, compared to 9.5 seconds for an FSI manual.


What about economy?
In the Jetta the TDI diesel model costs $35,490, $2500 more than the non-turbo FSI petrol model, but $4500 less than the FSI Turbo DSG.


The Carguide is assuming the price of diesel and petrol is approximately the same (true in Australia) and is driving in a mixed traffic condition (some city traffic, some freeway running and some secondary roads in the country that were speed limited to 80 km/h) with speed limit and safety in mind.

It is no surprise then that the diesel is the better in terms of fuel consumption over our drive, but that it did so well, returning 4.5 litres/100km average, is a pleasant surprise.

The FSI Turbo also proves a surprise in returning 6.7 litres/100km.


It is a little more complicated when calculating the non-turbo petrol. I'll leave this out here. You can read the original article if you are interested in the details.

Thus the $2500 price premium of the diesel would be recouped in 7000km [when the diesel is around $1.45]. That's about six months of average driving. After that you're laughing all the way to the bank.


In today, the price of diesel is about $1.20, so it may take longer to recoup the price premium. This is before Carsguide took into account biodiesel, which is an environmentally better choice. Jonathon Thwaites from University of Western Australia overcame all the legal hurdles and is manufacturing biodiesel in a shed at his home. Here is a write up. Here are some extracts:

For example 100 litres of oil will require approximately 20 litres of methanol with approximately 800 grams of KOH dissollved in it. These quantities must be determined in the titration and measured - not guessed. You will end up with 100 litre of biodiesel and about 20 litres of glycerine. I carry out 2 water washes (about 10 to 15 mins of my time each). So 100 litres of oil gives you 100 litres of biodiesel usually.

The total process probably takes about 2 hours but over about 2 days.

The cost of production (not including my time) is about 25 to 30 c per litre. I run my Hilux diesel ute on B100 100% biodiesel - and contrary to alot of reports I have read it has not destroyed my car yet - maybe this will happen some time but it seems to be working fine - maybe even better.


OK, you may have to invest in $3000 to buy a commercially produced reactor like Jonathon. Now, with slightly over $1 saving for each litre of diesel by using home-made biodiesel, you recoup the cost in about 35 km. (rough estimate by me)

By the way, to get more information about biodiesel, click here for Melbourne Biodiesel Club, Sydney Biodiesel Users Group or Brisbane Biodiesel in Australia.

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