Diesel Fuel consumption in Hot weather

And I was thinking that it was just me...

Over the past couple of weeks, you may have heard that Adelaide had some days that were a bit warmer than normal.

I noticed that not only did the fuel consumption increase, but that there was less power on take off. When I filled up on Sunday, the average was 12.81 L /100km for the last tank during the hot weather.

Normally, I am sitting at around 12.14 L/100km. Only difference has been the heat.

A few years ago, we would do the Melbourne - Adelaide run about every 6 weeks or so. Melb to Adl would be done in the early hours of the morning (leaving at 1:30am), whilst the return leg Adl - Mel would normally be done during daylight hours. This was done in a standard AU Fairmont.

Driving to Adelaide, we could make it door to door on one tank (just). Driving to Melbourne, we would fall about 40km short & had to fill up.

The only logical explanation for this, excluding things like traffic etc, is that the night air is cooler, therefore more dense, therefore has a better O2 content, therefore increases combustion.

During winter, we got better fuel consumption than summer too. Sure, the air conditioner will play a part, but over the same distance, same road, and same weight in the car, the only other significant difference was the outside temperature.

Hot and cold does affects fuel amounts, not so much when you are filling from an underground tank but in the bulk above ground tank side of things. To compensate this, fuel from the terminal is only charged out at the amount of fuel there would be @ 15 degrees C. From my time managing a fuel depot, most of the fuel was loaded at around 20 degrees C, there may have been 500 or 600 litres diference over a B double (55,000 litres). There is large losses in depots with above ground tanks especially in hotter areas, not uncommon for me to have 4000 or 5000 litres loss over a month, that was for diesel, unleaded was worse.

As been said before, underground tanks dont have large amounts of change in temp. As far as time of delivery, there is large amounts of varience. Majority of the time, fuel is delivered by contractors and they get there when they get there. Especially when they are travelling 500kms to deliver. No big conspiracy as far as delivering hot fuel.

I am not defending fuel companies, I dont work for them anymore, this is only my experience of running bulk fuel depots.

Cheers

Kieren

Quote:

---

Originally Posted by scarry

I mate of mine drives trucks interstate,& he swears that driving in the cool of night decreases fuel usage.I think the cooler air is denser & increases the efficiency of the engine,particularlya diesel.Thats why a larger intercooler helps.

Umm,always wondered how the different manufacturers get their ratings for their engines,if temperatures make a difference,i bet they are not rated at a certain temperature of,say,intake air.....

Just my 2 cents worth....

---

DIng give that man a prize.

engine ratings are usually determined by a local "ambient conditions" test on a dyno during initial manufacuture as part of quality control.

1 engine in say 10,000 will be set up for testing and not used beyond that, all aspects will be measured and it will be stripped down for tolerancing. anything amiss will result in quality changes on the line.

the cange in ambient conditions (atmospheric pressure, temp, humity) can account for up to 5% variation of the standard spec so what might be a 100Hp engine sold to iceland might only be a 95 hp engine if sold to africa.

Quote:

---

Originally Posted by scarry

I mate of mine drives trucks interstate,& he swears that driving in the cool of night decreases fuel usage.I think the cooler air is denser & increases the efficiency of the engine,particularlya diesel.Thats why a larger intercooler helps.

---

Certainly true that engines run more efficiently on cooler air, but the warmer and thinner air can also provide less wind resistance.

Interestingly I covered about 2000km in my work car last week (2.2 diesel, no turbo) and the best economy was driving in around 34 degree heat with the aircon blasting the whole way.:(