Differing Fuel Consumption
Discussion
I drive a Mondeo TDCI 140. The car is always warmed-up and almost every journey involves a motorway.
Indicated mean fuel consumption on a long, two-way motorway run (on cruise control 70-75mph) has been typically in the low 50s mpg.
Away from the motorway, I like to use the engine's performance and it does get a 'work-out'.
I recently added a bottle of Lucas fuel treatment to a full tank and deliberately drove the car a bit harder (and maintaining higher rpm).
Having re-fuelled, the subsequent 2 tanks of (BP and Total) diesel, the indicated fuel consumption rose to 60+ mpg (63/64 on longer runs) on cruise at 70-75mph. I believe that this is unlikely to be entirely a placebo effect, as the difference is fairly significant.
Having re-fuelled with Asda diesel on Friday, the indicated mean fuel consumption on the motorway was struggling to exceed 50mpg.
Weather conditions have not been significantly different in the past few weeks -Temperature has been fairly mild and winds haven't been particularly strong (all journeys have been round trips)
Questions:
Has the Lucas additive 'cleaned' the injectors? did it clean the head/pistons/anything else?
Does the benefit of this additive 'wear-off' quite quickly? Do Diesels 'clog-up' quickly?
Does the 'brand' of diesel make such a significant difference to fuel consumption? (I tend not to use supermarket diesel)
ps. My previous car gave much improved fuel consumption after a fairly throttle-heavy Euro road trip, but within weeks it was back to it's 'normal' level.
Indicated mean fuel consumption on a long, two-way motorway run (on cruise control 70-75mph) has been typically in the low 50s mpg.
Away from the motorway, I like to use the engine's performance and it does get a 'work-out'.
I recently added a bottle of Lucas fuel treatment to a full tank and deliberately drove the car a bit harder (and maintaining higher rpm).
Having re-fuelled, the subsequent 2 tanks of (BP and Total) diesel, the indicated fuel consumption rose to 60+ mpg (63/64 on longer runs) on cruise at 70-75mph. I believe that this is unlikely to be entirely a placebo effect, as the difference is fairly significant.
Having re-fuelled with Asda diesel on Friday, the indicated mean fuel consumption on the motorway was struggling to exceed 50mpg.
Weather conditions have not been significantly different in the past few weeks -Temperature has been fairly mild and winds haven't been particularly strong (all journeys have been round trips)
Questions:
Has the Lucas additive 'cleaned' the injectors? did it clean the head/pistons/anything else?
Does the benefit of this additive 'wear-off' quite quickly? Do Diesels 'clog-up' quickly?
Does the 'brand' of diesel make such a significant difference to fuel consumption? (I tend not to use supermarket diesel)
ps. My previous car gave much improved fuel consumption after a fairly throttle-heavy Euro road trip, but within weeks it was back to it's 'normal' level.
At the start of the year I had an issue with a fuel supplier I'd used for months. All of a sudden fuel consumption went up by about 15%
I had no idea why....but Asda was the same.
But chance another station close by had reduced it's price so I went there. Fuel consumption was restored
I do big miles, so any changes are quickly spotted. But that was the most extreme I'd ever seen it.
After 6 months avoiding them, I decided to go back to try. Seems their fuel has improved.
Of all the stations Ive tried though for diesel, I'd say Texaco was the best.
I had no idea why....but Asda was the same.
But chance another station close by had reduced it's price so I went there. Fuel consumption was restored
I do big miles, so any changes are quickly spotted. But that was the most extreme I'd ever seen it.
After 6 months avoiding them, I decided to go back to try. Seems their fuel has improved.
Of all the stations Ive tried though for diesel, I'd say Texaco was the best.
You will see a precentage FE reduction in approx Oct, that dissapears in approx March as the UK starts to use winter grade diesel, and then swaps back to summer grade fuel. The winter grade has anti waxing additives that have a lower calorific value, hence volumetric fuel consumption increases. On my car it is about 5-8% reduction typically. Generally, it is very obvious when the swapover has occurred, but natural changes in temp and weather in those months also move the mean FE around a bit too.
Re: fuel system cleaner. A modern common rail diesel is a "fuel mass" metered system. The driver demands a certain torque, and the injectors are commanded open for sufficient time to deliver a fuel mass that supports that torque demand. The exhuast AFR is only used to limit excursions into the rich shift direction (i.e. before you have boost and sufficient airflow, the maximum fuel mass is limited to prevent excessive rich mixture (the so called "smoke limit").
Hence, if you had clogged injectors, which were not delivering the correct fuel mass, then what would happen is engine torque output would be reduced. However, the driver of the car is also a closed loop system, and as such you would simply push the accelerator down a bit more until your choosen cruising speed was reached. As such, the only way, for a true fixed road load, that fuel economy could suffer is to reduce the conversion efficiency between fuel mass and torque. This is not really going to change, as it is set by mechanical factors such as compression ration, valve timing and injection timing etc.
Also "injectors becoming blocked" is not really a factor for a CR diesel. They operate at 2000bar, pretty much enough to actually cut through anything but high grade steel! What generally happens is that the injection nozzle wears, loosing the very defined geometry, and the fuel spray profile is changed. You loose the fine atomisation and a nice distributed spray cone. This tends to slow down the burn rate (larger more massive fuel particles "clumped" together). As a result there is a slight reduction in torque and generally a lot more soot formation. But fuel system cleaner is not going to be able to repair this wear!
Often the fuel system cleaner contains products that have a very high cetaine value. This high calorific value will increase the engines output for a given fuel mass, and if added to a fuel tank that hasn't got a large volume of fuel in it, can cause a noticable increase in economy! But if you work out the cost of the fuel additive, it is worse miles per £ than for normal diesel (hence the fuel companies don't put it in the normal fuel!)
Re: fuel system cleaner. A modern common rail diesel is a "fuel mass" metered system. The driver demands a certain torque, and the injectors are commanded open for sufficient time to deliver a fuel mass that supports that torque demand. The exhuast AFR is only used to limit excursions into the rich shift direction (i.e. before you have boost and sufficient airflow, the maximum fuel mass is limited to prevent excessive rich mixture (the so called "smoke limit").
Hence, if you had clogged injectors, which were not delivering the correct fuel mass, then what would happen is engine torque output would be reduced. However, the driver of the car is also a closed loop system, and as such you would simply push the accelerator down a bit more until your choosen cruising speed was reached. As such, the only way, for a true fixed road load, that fuel economy could suffer is to reduce the conversion efficiency between fuel mass and torque. This is not really going to change, as it is set by mechanical factors such as compression ration, valve timing and injection timing etc.
Also "injectors becoming blocked" is not really a factor for a CR diesel. They operate at 2000bar, pretty much enough to actually cut through anything but high grade steel! What generally happens is that the injection nozzle wears, loosing the very defined geometry, and the fuel spray profile is changed. You loose the fine atomisation and a nice distributed spray cone. This tends to slow down the burn rate (larger more massive fuel particles "clumped" together). As a result there is a slight reduction in torque and generally a lot more soot formation. But fuel system cleaner is not going to be able to repair this wear!
Often the fuel system cleaner contains products that have a very high cetaine value. This high calorific value will increase the engines output for a given fuel mass, and if added to a fuel tank that hasn't got a large volume of fuel in it, can cause a noticable increase in economy! But if you work out the cost of the fuel additive, it is worse miles per £ than for normal diesel (hence the fuel companies don't put it in the normal fuel!)
Cheers. My comparisons have been within the past month or so. I'm assuming that summer fuel has been used throughout this time.
A difference in consumption of ~24% could be described as significant.
What varies in the quality of the diesel fuel between suppliers? Is there a particular fraction of oil or a type of bio diesel (not)present in 'better' fuels?
-I wonder if the diesel purchased in other countries was of a higher 'quality'? I'm heading across Europe again in the near future, so I'll make a note of consumption.
I'll go back to my usual local BP or Total at the next fill-up to see if the fuel economy is significantly improved. The extra cost of 'brand-name' fuel may be worth it, although a bottle of additive per tank less so.
The car is 2.5 years old, 40-0dd K miles -It's not done massive mileage.
A difference in consumption of ~24% could be described as significant.
What varies in the quality of the diesel fuel between suppliers? Is there a particular fraction of oil or a type of bio diesel (not)present in 'better' fuels?
-I wonder if the diesel purchased in other countries was of a higher 'quality'? I'm heading across Europe again in the near future, so I'll make a note of consumption.
I'll go back to my usual local BP or Total at the next fill-up to see if the fuel economy is significantly improved. The extra cost of 'brand-name' fuel may be worth it, although a bottle of additive per tank less so.
Max_Torque said:
Re: fuel system cleaner. A modern common rail diesel is a "fuel mass" metered system. The driver demands a certain torque, and the injectors are commanded open for sufficient time to deliver a fuel mass that supports that torque demand. The exhuast AFR is only used to limit excursions into the rich shift direction (i.e. before you have boost and sufficient airflow, the maximum fuel mass is limited to prevent excessive rich mixture (the so called "smoke limit").
That's how I understood it to be. As you say, the driver presses the pedal further until the required torque is delivered.Max_Torque said:
Also "injectors becoming blocked" is not really a factor for a CR diesel. They operate at 2000bar, pretty much enough to actually cut through anything but high grade steel!
That is what I was thinking. I certainly wouldn't want to put my hand in front of that kind of jet if I didn't want a hole throught it!The car is 2.5 years old, 40-0dd K miles -It's not done massive mileage.
Max_Torque said:
Often the fuel system cleaner contains products that have a very high cetaine value. This high calorific value will increase the engines output for a given fuel mass, and if added to a fuel tank that hasn't got a large volume of fuel in it, can cause a noticable increase in economy! But if you work out the cost of the fuel additive, it is worse miles per £ than for normal diesel (hence the fuel companies don't put it in the normal fuel!)
I wasn't convinced by the claims on the tuneup/injector cleaner bottle and it claimed t suitable for petrol and for diesel, but I thought I'd give it a try for 5quid or so, as I didn't think that a dose of only 155ml in 70 litres of diesel would do much harm (or benefit?!). I suspected it may be an expensive Placebo. Edited by MC Bodge on Sunday 24th June 14:19
I run a small fleet of diesels running on, exclusively, Texaco fuel.
Occasionally, up until last year, for convenience and price, we would refuel at a supermarket outlet (also starts with a T) and consumption figures would vary.
The reason became apparent when a driver, with just under a quarter showing on the fuel guage, filled the tank with 72.7 litres ----the tank only holds 70 litres!
We tried with other vehicles with similar results and made representations to the chain and then to trading standards, however they are a huge company and the pumps had been calibrated and certified the previous week!!
Any problems may not be with the vehicle.
Occasionally, up until last year, for convenience and price, we would refuel at a supermarket outlet (also starts with a T) and consumption figures would vary.
The reason became apparent when a driver, with just under a quarter showing on the fuel guage, filled the tank with 72.7 litres ----the tank only holds 70 litres!
We tried with other vehicles with similar results and made representations to the chain and then to trading standards, however they are a huge company and the pumps had been calibrated and certified the previous week!!
Any problems may not be with the vehicle.
No it isn't, On board is variable. The only way to do this properly is brim to brim manually working out the consumption. (Technically, at the same pump in the same fuel station at the same time of day, with the same temperature etc. etc.)
If not you are comparing apples with oranges.
If not you are comparing apples with oranges.
Ive only ever had one station selling less then they claimed. it was in Dundalk, Ireland
The managed to squeeze 49 litres into my tank which probably had 10 litres left.
Normally when the light is on I can get 43-44 litres at.....they must have worked some magic ! In the instance above the light was still 40-50 miles away !
If it wasnt for the fact I go through so much fuel, I wouldnt even have noticed it.
But every fill is 43-44 litres and I go through that most days.
The managed to squeeze 49 litres into my tank which probably had 10 litres left.
Normally when the light is on I can get 43-44 litres at.....they must have worked some magic ! In the instance above the light was still 40-50 miles away !
If it wasnt for the fact I go through so much fuel, I wouldnt even have noticed it.
But every fill is 43-44 litres and I go through that most days.
Bennachie said:
No it isn't, On board is variable. The only way to do this properly is brim to brim manually working out the consumption. (Technically, at the same pump in the same fuel station at the same time of day, with the same temperature etc. etc.)
If not you are comparing apples with oranges.
I assume that the on-board consumption is derived from fuel delivery (injection pulse width, or maybe fuel header loop top-up flow?) and distance travelled.If not you are comparing apples with oranges.
The numerical units may be inaccurate, but driving a motorway at a comparable speed in the same gear should give a reasonably repeatable, similar outcome given a a similar fuel 'density' to allow a reasonable comparison from one week to the next.
Given the same conditions, I wouldn't expect that a difference of 24% was purely down to inconsistency in the on-board fuel consumption calculation.
Edited by MC Bodge on Tuesday 26th June 09:27
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