Wednesday, September 25, 2013

How does E10 (ethanol) petrol compare with unleaded petrol?

I thought it would be interesting to run a few tests with E10 petrol (up to 10% ethanol) and compare the fuel consumption result with standard unleaded petrol. I'd read literature on the internet and found the following.

Ethanol has a lower energy content than standard petrol and thus it is expected you'll get less kilometres for the same amount of petrol. E10 petrol is typically around 3 cents per litre cheaper. The RACQ site states you should expect around a 3% increase in fuel consumption. Whilst we can simply believe what we read, I prefer to perform my own tests. The reason I want to perform my own tests is whilst ethanol has a lower energy content, E10 has a higher octane rating, and a higher octane level (95 as compared with 91 for unleaded) is associated with improved petrol consumption. Performing a series of tests will provide the information I desire.

Test 1 – City driving

Filled the tank with 45 litres of E10 petrol. The tank capacity is 60 litres. That means around 25% of the fuel is still unleaded.

I next filled the tank with 48.22 litres; the distance travelled was 462.7 km. 

This gives a fuel consumption figure of 10.42 litres per 100 km.

This result was unexpected. Normally I consistently fill up the tank with around 50 litres of petrol having travelled around 450 km, or around 11.11 litres per 100 km. I had used less petrol and had gone further. This is opposite to what I'd read on the internet and expected. Since ethanol has a lower energy content from the articles I read I was expecting to get less than 450 km, but instead achieved more.

This is the first test. I like to perform three tests and then average the results. Unfortunately the test was interrupted with the next tank being used for country driving. I will return to perform further tests for city driving.

Test 2 – Country driving

Filled the tank with 41.38 litres of E10 petrol; the distance travelled 531.9 km.

Fuel consumption  7.78 litres per 100 km.

I currently do not have any country driving comparison with standard petrol, but in the future I hope to perform additional country driving tests.

The litres per 100 km calculator is available at for those who wish to perform their own tests and calculations. As I complete further tests I'll publish the results on this page.

8 October 2013
Filled tank with 44.24 litres of E10; the distance travelled 412.6 km.
Fuel consumption 10.72 litres per 100 km.

9 November 2013

Filled tank with 48.97 litres of E10; the distance travelled 444.4 km.
Fuel consumption 11.02 litres per 100 km.

Based on the three test with the results of 10.42, 10.72 and 11.02 litres per 100 km the average fuel consumption for city driving for my Toyota Avensis is 10.72 litres per 100 km. The variation is 0.3 L / 100 km or 2.8% variation.

I'll now perform three tests for city driving using regular unleaded petrol.

Kelvin Eldridge
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PS. The result of the first city driving test is improved fuel consumption whereas the expectation was fuel consumption would be degraded. Further testing is now being done to verify this figure. I would suggest those using E10 perform their own tests.

Update: 5 January 2014
Three more tanks of petrol. City driving.
14/12/13  Unleaded 52.41 L, 495.1 km - 10.59 L / 100 km
22/12/13  Unleaded 49.86 L, 461.1 km - 10.81 L / 100 km
31/12/13  Unleaded 28.32 L, 266.3 km - 10.63 L / 100 km
Average 10.67 L / 100 km +/- 0.14 L / 100 km or 1.31% variation.

Based on this limited testing using my normal day-to-day city/suburban driving, the fuel usage difference between Unleaded and E10 is on average 0.05 L / 100 km. This is an increase in petrol usage of 0.46%, which is much less than the RACQ information.

Logically ethanol has around 30% less energy than petrol. Since E10 uses 10% ethanol that means E10 would have 3% less energy. Using E10 we should see an increase in fuel consumption per 100 km. We do see an increase but not by that amount.  In this test we saw an increase of 0.46%.

I suspect that whilst E10 does have less energy, the increase in the octane rating counters this to a degree and thus we don't see as great an increase in fuel consumption as expected.

E10 at the local service station is typically priced 3 cents a litre cheaper than unleaded fuel. At current petrol prices of around $1.60 a litre, 3 cents is a saving of 1.8%. This saving is reduced by the increased fuel consumption of 0.46% leaving us with a saving of 1.34%. Keep in mind there is no guarantee this saving even exists as the variance in the measurements exceeded this percentage, but if we assume this saving exists, how much saving a year would this mean.

First the petrol stations I use to purchase E10 don't take discount vouchers from the leading supermarkets. A voucher saving would exceed any E10 saving. But lets assume you don't use vouchers.

I do about 14,000 kilometres per year. Using the Petrol Cost Calculator I can determine I'd use an estimated $2,473 of petrol a year. A 1.34% saving would be $33 a year.

It has taken a while to get to this point in this testing and analysis, but since I don't consider a $33 saving over a year to be a  significant amount, and I always have a discount voucher available often far exceeding the E10 discount, it makes little sense to choose E10 over unleaded petrol from a service station which accepts discount vouchers. If the service station you use has both E10 and unleaded, and you're happy to use E10 and believe it won't adversely cause problems with your car,  then a small saving may be possible with E10.

Personally I am concerned United Petroleum doesn't promote greater fuel economy as a benefit of using E10 on their site. If the company selling the petrol doesn't see this as a benefit which can be promoted, then that begs the question why. I also have a lingering concern that since ethanol is hydroscopic (attracts water), and water can damage the fuel system, is there an increased risk to causing damage to the car. I haven't been fully convinced the additives may counter the issues but perhaps with more reading those fears could be allayed. The increased risk factor, small potential savings, and other ways to make greater savings using discount vouchers, does sway me towards not considering E10 in the future. You may come to a different conclusion.

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