Coach fuel consumption

Thanks to an extensive database Volvo Bus can present detailed fuel consumption data from real use on a yearly average. In the example below my colleague Anders Tuomivaara has aggregated data for Sweden, Finland, Denmark, Germany, Poland, Netherlands, Belgium, UK, at real world conditions far from the laboratory.

In 2006 Volvo Bus and the DH12 (in B12B and B12M buses) engines secured a leading position in fuel consumption in real use on a yearly basis. The breakthrough came with a new engine generation in combination with a new gearbox, the now a days legendary I-Shift. The fuel consumption was determined to in average 26 liter per 100 km (for the average speed of 60 km/h), including all idle and auxiliaries such as air conditioners and winter heaters.
When Volvo Bus introduced the 13 liter engine in 2010 the forecast said an expected average fuel consumption decrease by 4-5% depending on the average speed. We have now gathered enough data to confirm that the average saving is 4-6% in real operation.

Several factors have high impact on the fuel consumption. In the data below we have grouped the coaches in three groups. Coaches with a yearly average speed of 35-45 km/h are represented by the speed 40 km/h. The group with speeds between 45 and 55 are plotted as 50 km/h and so on. Note that at constant speed the fuel consumption increase with higher speed, this mostly not the case in real operation of buses.

volvo 9700 yearly average fuel consumption

Graph: Fuel consumption for a 9700 12 meter with 4×2 axle configuration one example automatic gear box is compared to the I-Shift gear box plotted for average speed of 40, 50 and 60 km/h.

 

Last year, 2012, Volvo Buses presented another new engine range for coaches based on the D11 engine. Although we have not yet a full year of data we have an indication that we are heading in the right direction. Even if the decimals are not in place we have now enough information to state that the superior fuel consumption of the new product line is confirmed, again.

 volvo 9700 yearly average fuel consumption

Graph: Fuel consumption for a 9700 13.5 to 14.5 meter with 6×2 axle configuration with the I-Shift gear box plotted for average speed of 40, 50 and 60 km/h.

 

We are immensely proud of our new engine technology that has been realized by our engine development colleagues at Lundby and Lyon.  And, it will continue to progress already by the end of the year, when introducing the Euro VI engines. One of the secrets behind the progress for the larger 6×2 coaches is that the new D11 engine has the same power output as we have for the larger D13 engine.

And, I am immensely proud of our contribution to the lower emissions of greenhouse gases. Coaches in general have a filling factor of about 60%. On some markets it is higher and on other markets it is a bit lower.

 

Carbon dioxide emissions per passenger kilometer (g CO2/km) for Volvo 9700 4×2 12 meter, with the new D11 engine range.

  Average Speed km/h

PAX

40

50

60

30

24

22

21

40

19

17

16

Carbon dioxide emissions per passenger kilometer (g CO2/km) for Volvo 9700 6×2 14.5 meter, with the new D11 engine range.

  Average Speed km/h

PAX

40

50

60

40

20

18

18

50

16

15

14

60

15

13

12

Note that the data above are average European numbers, higher values are expected in the Alps and lower values are expected in the flat countries.

About volvobuses

Adjunct Professor of Catalysis at Chalmers University of Technology. Lives in Gothenburg, Sweden, with my wife and three daughters born in 1991, 1994 and 1997. Is a passionate runner.
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11 Responses to Coach fuel consumption

  1. Paul Rodrigues says:

    Extremely interesting data. Can Volvo ”crunch” similar data for the Volvo 7900 Hybrid series in the near future?

  2. volvobuses says:

    Yes, let me come back within shortly with a detailed report

  3. Guérin says:

    When we can see that average consumption decrease when average speed increase, it do not means that actual consumption decrease when actual speed increase: its the contrary.
    results on average values are linked with bottle necks and idle speed when consumption in litre/100km go to infinity…

  4. Guérin says:

    The here-above results which show that average consumption increase when average speed decrease show that it would be important to decrease consumption for low average speed.
    For low and very low bus speed, the consumption is due to engine idle speed consumption which is linked with engine displacement and engine speed.
    To reduce these engine low charge consumption, the best way is to use the DCCE (Dual Cranshaft Cocept Engine) which look like two engines (which could be in the same block).
    – The smaler one working continusly with alternator, AC compressor, air compressor etc… its max power beeing 1/3 to 1/4 of the curent engine.
    – The bigger one (the “booster”) working only when needed (hard acceleration, high speed, slopes etc…
    – These two engines beeing loked together with a free weel.
    – This concept allow very great consumption savings in urban uses.
    For more informations on this concept, contact me.
    Best regards.

    • volvobuses says:

      Several factors contribute to the higher fuel consumption at lower average speed: idle share goeas up, driving pattern becomes different, etc.
      In average slower buses have more stops and lower average power than at the higher speeds.
      Still the power is needed to secure that the coach can keep-up with the time table.
      Historically, in the reaserch, several several trials have been made with multiple drive trains in combination with free-wheel and power banks.
      Conceptually it is interesting, however mostly the weight, cost and complexity makes it less competitive for many of the applications.

      • Guérin says:

        My comment was to say that it’s not the speed limit which is responsible of consumption increase when average speed decrease but the fact that at slow average speed the consumption is more due to engine consumption than to enregy delivered to the weels…

      • Guérin says:

        My comment was to say that it’s not the speed limit which is responsible of consumption increase when average speed decrease but the fact that at slow average speed the consumption is more due to engine consumption than to enregy delivered to the weels…
        If we consider that total consumption is due to:
        – engine consumption to turn itself: 1/3 liter/hour per litre of displacement and per 1000 RPM: 2 L/h for a 6 litre displacement runing at 1000 RPM: 5 litre per 100km at 40 km/h.
        – consumption to deliver energy to the weels: 1/4 litre/hour per kW: 8l/h for 32 kW: 20 l/100km at 40km/h.
        DCCE is able to reduce drastiquely the engine consumption to turn itself as displacement downsizing.

  5. Great report , please email to me future updates .

    Maurice Byrne ,

    • Guérin says:

      First of all, excuse me for my bad english writing.

      G‌ood morning.

      this blog is very interesting.
      their is a good analyse of the reason of consumption increasing at low average speed: the % of consumption needed to make the engine runing increase.
      starting from that fact, the way to save a lot of consumption is to minimise the consumption needed to make the engine runing.
      and the most efficient way is to drastiquely minimise the engine volume during the time few power is needed.
      my proposal is to use two engines:
      – a small one (1/4 of the sole one) for electricity, AC and low speed (low power) needed => 75% of fuel saving to make the engine runing…
      – a booster (3/4 of the sole one) only used for slopes, acceleration or high speed.
      Tell me how to give you a “ppt” showing that.

      Dominique Guérin
      6 chemin de la Gare et 2 chemin de Guilhon
      76630 Sauchay 31420 Cassagnabère-Tournas
      0235857075 0567558899

      • volvobuses says:

        Dear Domonique,
        I hope you are well.

        For buses and coaches the auxiliary loads are substantial.
        The slower the speed the more the power to auxilliaries increase in absolute terms, when reported per kilometer.
        Twin engines or cylinder cut-off are interesting concepts that however so far have turned out relatively expensive and service intens.
        Please send your powerpoints to our external mailbox: citymobility@volvo.com

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