Seasonal affect on diesel engine fuel economy
Seasonal affect on diesel engine fuel economy
(OP)
Hello,
I am new to this forum today so if I am not posting this question in the proper place please correct me.
I am trying to factor out seasonal affects on fuel economy in a fleet if municipal buses so that I can better evaluate certain proposed fuel saving measures. Does anyone have data on this? The fleet is in North Carolina. The engines are primarily Cummins. The fuel is LSD.
I am new to this forum today so if I am not posting this question in the proper place please correct me.
I am trying to factor out seasonal affects on fuel economy in a fleet if municipal buses so that I can better evaluate certain proposed fuel saving measures. Does anyone have data on this? The fleet is in North Carolina. The engines are primarily Cummins. The fuel is LSD.





RE: Seasonal affect on diesel engine fuel economy
respectfully
RE: Seasonal affect on diesel engine fuel economy
The heat value is related to mass and the fuel is actually metered by volume, hence SG is critical.
Also, warm up times and manner of use might change due to weather. Passenger travel patterns might also change, so there will be factors other than MPG that impact on the amount of fuel used.
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RE: Seasonal affect on diesel engine fuel economy
Depending on the age of the engines, you could be wrong: current Cat engines (I know, the buses have Cummins, but I know about the Cats) try to meter by mass by inferring the spec grav. from the fuel temperature.
Thus, the engine will burn a larger volume of fuel in hot weather than in cold weather, but the guy measuring the "fuel economy" will be measuring only gallons, and so will show worse fuel economy for hot fuel than for cold.
VGS: You certainly need to compensate for temperature when measuring fuel economy, or your numbers will be at best misleading. You should also regularly sample the fuel yourself for spec grav., since your supplier probably won't know.
Finally, the grade of fuel is important, whether it's number 1 or number 2; these typically have very different cetane numbers and could well have other differences that affect fuel mileage.
RE: Seasonal affect on diesel engine fuel economy
Hotter weather means less dense fuel, but also generally less dense air. The air density has an effect on both A:F and aero drag.
Regards
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.
RE: Seasonal affect on diesel engine fuel economy
Thanks, and keep the ideas coming if any new ones come to mind.
RE: Seasonal affect on diesel engine fuel economy
Then we make a modification to one of them, and run another series of comparison runs, both the modified and the baseline vehicles.
We run both trucks on the same route, same time, same day.
Not close together, of course, but within a minute or two of each other, so that both experience the same traffic, wind, temperature, etc. conditions.
The fueling process itself is almost the subject of another full discussion, but suffice it to say we do our best to compensate for variations in fuel temperatures and for the variation in apparent fuel level during fueling.
We're careful always park the truck in exactly the same place when fueling, and to only fuel one tank, in order to avoid trying to compensate for fuel transfer between tanks.
We have found, incidentally, large variations between the fuel mileage number obtained by our measurements, and the fuel mileage number computed by the engine control computer.
The ECM infers fuel usage from injector rate and pulse-width rather than actually measuring fuel flow, and tries to compensate for volumetric changes using fuel temp, but Caterpillar at least have a defective algorithm, so their result varies wildly, and is effectively useless.
RE: Seasonal affect on diesel engine fuel economy
For example, when I was at UNC several routes had to add extra buses when it rained and folks didn't ride their bikes or walk to campus, so I'll bet they got worse mileage when it rained- but was it from the wet?
RE: Seasonal affect on diesel engine fuel economy
Unless of course you're willing to wait months or years to accumulate enough data for daily variations in ridership etc. to average themselves out.
RE: Seasonal affect on diesel engine fuel economy
If anyone knows of someone who might like to get involved in a more direct test like Rob45 suggests (a manufacturer, fleet manager, or end user) I'd like to talk to them. If this request violates forum policy, please delete it.
RE: Seasonal affect on diesel engine fuel economy
Lube oils in axles and hubs has a higher viscosity and hence more drag. Same in the trans. Some fleets are slow to adjust tire air pressures to compensate for seasonal changes, so tires can be softer.
Lots of variations enter into the picture.
rmw
RE: Seasonal affect on diesel engine fuel economy
Why don't you contact the bus mfr and the engine mfr, see if you can get them interested in a joint project?
They might be interested since fuel economy seems once again to have gotten important, at least for a while.