Fuel efficiency of John Deere 5075M versus John Deere 5085M

[Redneck in training]

Another thing that affects efficiency is cooling. Large volume cylinders have smaller surface relative to diplacement to cool. Therefore they have less energy lost by cooling. Specific fuel consumption of the Vartsila diesel is less than half of the specific consumption of the JD diesel. Needless to say the Vartsila burns heavy oil that might have somewhat greater energy content than road diesel fuel.

 

[buickanddeere]

Correct. For example a 300cu" six cylinder engine looses more heat to the cooling system than 300cu" two cylinder engine. That heat could have instead been used to expand the gasses in the combustion chamber and make more pressure.
The 300cu" six however can be built to have higher volumetric efficiency at elevated rpms.

 

[MHarryE]

If more cylinder for the same displacement meant better efficiency a Ferrari V-12 would be fantastic compared to the same displacement in fewer cylinders. Many things enter in like friction - add the circumference of all cylinders, extra rod and main bearings.

With Tier 4 interim and final, one way companies are holding down costs and improving fuel economy is by reducing the number of cylinders. Lower swept area, fewer parts, all reduce cost, reduce parasitic losses. Until the last decade there was not a lot of technology improvement in diesels. In the mid-60's it was add a turbo to get more oxygen into the cylinders and crank up the fuel with no significant difference in injection systems. There were gains due to getting more power from the same displacement but a small increment.

The injector pressure of our old 1939 TD-6 International was 740-750 psi. The injector pressure of my Kubota L5740 is 2000 - 213- psi, not a huge difference over 70 years. A good Tier 4 final engine will be over 30,000 psi. Diesel doesn't vaporize like gasoline - the high pressure breaks the injected fuel into droplets; higher pressure, finer droplets, more fuel burned, less unburned fuel going out the stack.

GPH at full power is not a very good indicator. If it meant anything our L5740 would be the most efficient tractor on our farm but in fact it is the least efficient except at light duty chores for which it is designed. Our John Deere 7720 is most efficient when it comes to full power work. Like comparing the 5075 and 5085 at max power. The 5085 uses more fuel because it is producing more power. The significant item is pounds per hp-hr. If you are using these tractors with a 6 foot finish mower the 5075 will use less fuel but if you are using both tractors at the power limit of the 5075, the 5085 will use less fuel.

 

[Redneck in training]

Correct. For example a 300cu" six cylinder engine looses more heat to the cooling system than 300cu" two cylinder engine. That heat could have instead been used to expand the gasses in the combustion chamber and make more pressure.
The 300cu" six however can be built to have higher volumetric efficiency at elevated rpms.

The problem is mechanical limits of reciprocating mass and medium piston speed. Power of combustion engine is proportional to mass flow of air (oxygen) through the engine. Multiply 2 liters times 20000 rpm times filling efficiency times specific mas of air. Then add proportional amount of fuel etc. F1 2 liter engine produces about 800 HP at 25000 rpm but I doubt it is too efficient. F1 car does about 2 mpg. To increase power you can either increase volume or rpm. Vartsila diesel runs max about 100 rpm due to large reciprocating mass but it is the most volumetric efficient engine. Vartsila is turbo charged. Vartsila has 4.28 HP/ liter while F1 engine has about 400 HP/liter. Another thing is engine life. I am guessing Vartsila will run in excess of 10000 hours before overhaul. I doubt F1 engine will make 10 hours.

 

[Redneck in training]

If more cylinder for the same displacement meant better efficiency a Ferrari V-12 would be fantastic compared to the same displacement in fewer cylinders. Many things enter in like friction - add the circumference of all cylinders, extra rod and main bearings.

I used to know a guy (about 35 years ago) who inherited Ferrari that he wanted to sell. When people interested in the car asked to start it he asked for gas money. The car would do about 6 mpg at normal driving and 1.5 mpg at high speed.