Fuel Saving Techniques
The national average mpg is around 6 mpg. With a proper understanding of the physics that affect fuel consumption it is relatively easy to move out of this average group and achieve 7.5 mpg or more. Fuel conscious fleets have been in the high eights and I know Owner/Operators running a life time average of over 9 and even 10 mpg, both in new trucks with lots of technology and trucks 10 years or older.
The national average mpg is around 6 mpg. With a proper understanding of the physics that affect fuel consumption it is relatively easy to move out of this average group and achieve 7.5 mpg or more. Fuel conscious fleets have been in the high eights and I know Owner/Operators running a life time average of over 9 and even 10 mpg, both in new trucks with lots of technology and trucks 10 years or older.
The first and most important thing to understand is we are all playing on a level playing field.
All modern diesel engines will produce almost identical mpg results in identical load situations.
The fuel in your tank along with atmospheric air is the energy that propels your truck down the road. The energy in your diesel fuel is limited to 139,000 btu, slightly less for bio diesel, and all modern diesel engines will produce almost identical mpg results in identical load situations assuming they have the same set of circumstances, driving style, ECM settings, etc. It is determined by the laws of thermodynamics. For more in depth facts about fuel, check out Fuel Facts. (Link to Fuel facts under Facts that Affect MPG)
Engine Manufactures are under extreme pressure, not only from government but also to keep up with their competitors.
Example: The Detroit Diesel Dd15 is the result of $1.5 Billion; yes that’s $1,500,000,000 dollars and nearly five years of development.
So before you start trying to improve engine efficiency just remember this: The energy in one gallon of diesel will produce just a little over 20 hp per hour in nearly every after-cooled, turbo equipped over the road diesel engine on the market today. Regardless of what you hear at the truck stop lunch counter, rarely will you see over a 4 - 5% difference from one major engine manufacture to the next. This, I believe is the reason engine manufactures no longer make the BSFC (fuel consumption) rates of their engines available to the public. No engine designer has an advantage worth talking about. So remember, it’s not about the engine brand. It’s all about managing how that engines power is used.
There are fleets and owner/operators running many different models, Detriots, Volvos, Internationals, Cummins, Cats etc. and averaging in the high eights with some individuals as high as 10+ mpg.
To improve your mpg using engine modifications will prove to be very expensive and challenging with minimal return. In most cases running a gallon of fuel through your engine will return 20 to 22 hp per hr unless you’re doing some costly modifications and know what you are doing. And even then the return on investment will likely be less than many other fuel saving techniques available today.
It’s all pretty simple really.
Just remember, if your engine is producing 20 HP per hour per gallon of fuel it burns and you are burning fuel at a rate of 10 gallons per hour your engine is producing about 200 hp. Ten gallons per hour (gph) at 60 mph is 6 mpg and at 70 mph it’s 7 mpg. But, assuming your physical load has not changed, the increase in wind resistance will require an extra 60 or more hp. This will eat up another 3 to 4 gph in fuel. So, you will typically end up losing about 1 mpg with each 10 mph in increased speed unless you have a perfect tail wind in your favor. In other words, grab another gear to take advantage of a good tail wind and slow down in a side or head wind as explained in more detail in the “Driving for MPG” section of this site.
Because improving mpg by even 5 to 10% by modifying your engine will be costly and questionable I recommend you focus first on the most cost effective and largest factor, the driver, a 30% variable in fuel consumption. Then move on to aerodynamics etc. to reduce the load on your engine.
Less load = Less fuel
As you scrolled through the above “Rock-Solid Rules” you probably noticed that the biggest fuel saver is the driver, “The most efficient drivers get about 30% better fuel economy than the least efficient drivers.”
Kenworth’s chief engineer, Kevin Baney says, “Everyone drives a truck differently, and the fuel economy range between a fleet’s top driver and lowest performer can exceed 1 mpg,”
The first and most important thing to understand is we are all playing on a level playing field.
All modern diesel engines will produce almost identical mpg results in identical load situations.
The fuel in your tank along with atmospheric air is the energy that propels your truck down the road. The energy in your diesel fuel is limited to 139,000 btu, slightly less for bio diesel, and all modern diesel engines will produce almost identical mpg results in identical load situations assuming they have the same set of circumstances, driving style, ECM settings, etc. It is determined by the laws of thermodynamics. For more in depth facts about fuel, check out Fuel Facts. (Link to Fuel facts under Facts that Affect MPG)
Engine Manufactures are under extreme pressure, not only from government but also to keep up with their competitors.
Example: The Detroit Diesel Dd15 is the result of $1.5 Billion; yes that’s $1,500,000,000 dollars and nearly five years of development.
So before you start trying to improve engine efficiency just remember this: The energy in one gallon of diesel will produce just a little over 20 hp per hour in nearly every after-cooled, turbo equipped over the road diesel engine on the market today. Regardless of what you hear at the truck stop lunch counter, rarely will you see over a 4 - 5% difference from one major engine manufacture to the next. This, I believe is the reason engine manufactures no longer make the BSFC (fuel consumption) rates of their engines available to the public. No engine designer has an advantage worth talking about. So remember, it’s not about the engine brand. It’s all about managing how that engines power is used.
There are fleets and owner/operators running many different models, Detriots, Volvos, Internationals, Cummins, Cats etc. and averaging in the high eights with some individuals as high as 10+ mpg.
With that in mind check out what Cummins engine manufacture has to say in their paper titled:
“Secrets of Better Fuel Economy” The Physics of MPG.
They list these ten “Rock-Solid Rules”
Aerodynamics:
• Every 2% reduction in aerodynamic drag results in approximately 1% improvement in fuel economy.
• Above 55 mph, each 1 mph increase in vehicle speed decreases fuel economy by 0.1 mpg.
Tires:
• Worn tires provide better fuel economy than new tires, up to 7% better fuel economy.
• Used lug drive tires can get up to 0.4 mpg better than new lug tires.
• Ribbed tires on the drive axles provide 2–4% better fuel economy than lugged tires.
• Every 10 psi that a truck’s tires are underinflated reduces fuel economy by 1%.
• The break-in period for tires is between 35,000 and 50,000 miles.
• Tires make biggest difference in mpg below around 50 mph; aerodynamics is the most important factor over around 50 mph.
Power Management:
• The most efficient drivers get about 30% better fuel economy than the least efficient drivers.
Idling Waste:
• Idle time is costly. Every hour of idle time in a long-haul operation can decrease fuel efficiency by 1%.
Notice that every secret they list is about reducing the load on your engine and has nothing to do with engine design itself.
Cummins has done an excellent job of expanding these points in further detail in the paper here and it is definitely worth the read.To improve your mpg using engine modifications will prove to be very expensive and challenging with minimal return. In most cases running a gallon of fuel through your engine will return 20 to 22 hp per hr unless you’re doing some costly modifications and know what you are doing. And even then the return on investment will likely be less than many other fuel saving techniques available today.
It’s all pretty simple really.
Just remember, if your engine is producing 20 HP per hour per gallon of fuel it burns and you are burning fuel at a rate of 10 gallons per hour your engine is producing about 200 hp. Ten gallons per hour (gph) at 60 mph is 6 mpg and at 70 mph it’s 7 mpg. But, assuming your physical load has not changed, the increase in wind resistance will require an extra 60 or more hp. This will eat up another 3 to 4 gph in fuel. So, you will typically end up losing about 1 mpg with each 10 mph in increased speed unless you have a perfect tail wind in your favor. In other words, grab another gear to take advantage of a good tail wind and slow down in a side or head wind as explained in more detail in the “Driving for MPG” section of this site.
Because improving mpg by even 5 to 10% by modifying your engine will be costly and questionable I recommend you focus first on the most cost effective and largest factor, the driver, a 30% variable in fuel consumption. Then move on to aerodynamics etc. to reduce the load on your engine.
Less load = Less fuel
As you scrolled through the above “Rock-Solid Rules” you probably noticed that the biggest fuel saver is the driver, “The most efficient drivers get about 30% better fuel economy than the least efficient drivers.”
Kenworth’s chief engineer, Kevin Baney says, “Everyone drives a truck differently, and the fuel economy range between a fleet’s top driver and lowest performer can exceed 1 mpg,”