1. Off-Road Equipment Management TSM 262: Spring 2016
LECTURE 5: Tractor Performance II
Off-Road Equipment Engineering
Dept of Agricultural and Biological Engineering

2. Homework and Lab

3. Class Objectives Students should be able to:
Analyze the relationships between engine speed, torque, power, and fuel consumption for diesel engines used in off-road applications
Estimate average fuel consumption for a tractor or combine
Understand the “shift up and throttle back” process for achieving better fuel economy
Understand the basic working principles of an engine
Analyze the pulling performance and tractive efficiency of a tractor

4. Brake Thermal Efficiency
How is brake thermal efficiency calculated?
From fuel
PPTO = Power measured at PTO [kW]
FC = Fuel consumption [kg/h]
HV = Gross calorific value for fuel [kJ/kg]
HV - diesel fuel = 45,500 kJ/kg
HV - biodiesel = 38,000 kJ/kg
HV – ethanol = 29,000 kJ/kg

5. Example Problem
Engine manufacturers strive to achieve 40% or higher brake thermal efficiency. If an engine runs on diesel fuel with a gross calorific value of 45,500 kJ/kg, what SFC should the manufacturer be targeting?
What happens to SFC when burning biodiesel or ethanol?

6. Engine Performance Map
Add contours of constant SFC and constant power to load-speed graph

7. “Shift Up & Throttle Back” Concept

8. “Shift Up & Throttle Back” Concept
When tractor is operating at less than full load, operator is advised to shift up to a higher gear and reduce engine speed to retain original ground speed
How does this improve fuel economy?
At Pb = 20 kW:
BSFC > 400 full speed
BSFC = rev/min
Savings in fuel = ( )/400
= 27.5% !!

9. Map Examples
Ford 2.5L DI engine
Ford 2.5L DI turbocharged engine

10. Estimation of Average Fuel Consumption
Annual average fuel requirements for tractors or other diesel engine driven machinery may be used in calculating overall machinery costs for particular enterprise
Fuel requirement for particular operation should be based on actual power required
If available, make use of data from Nebraska tests:

11. Estimation of Average Fuel Consumption
Method of estimation given in ASAE Standard D497.7
Equation for predicting SFC (specific fuel consumption in L/kWh) based on Nebraska tractor test data
Applies to diesel tractor and combine engines
Standard includes:
Fraction of equivalent PTO power available
Partial throttle multiplier that accounts for adjustments in engine speed
Why are these two factors included?

12. Estimation of Average Fuel Consumption
SFC (L/kWh) for Diesel:
X = equivalent PTO Power required by operation ÷ maximum available from PTO
nPT = partial throttle engine speed, rpm
nFT = full throttle engine speed, rpm

13. Shift up-throttle back
Vary X
Vary N
X = Equivalent PTO Power required by operation/Rated PTO Power
N = Partial throttle engine speed/full throttle engine speed

14. Example Problem
An AGCO Allis 9775 tractor fitted with a Cummins engine has a rated PTO power of 152 kW at 2200 r/min and its maximum high idle speed is 2430 r/min. While cultivating a field on average the tractor uses the equivalent PTO power of 80 kW with the throttle setting at 2000 r/min
Calculate the SFC in L/kWh

15. Solution Given Solution Rated PTO power = 152 kW
Rated speed = 2200 r/min
High idle speed = 2450 r/min
For cultivating tractor uses only 50 kW
Throttle setting at 2000 r/min
Solution
X = 50/152 = 0.33
N=2000/2450 = 0.82
PTM = 1-(N-1)(0.45*X-0.877)
PTM =1-(0.82-1)(0.45* )= 0.869
SFC =( /X)*PTM=( /0.33)*0.869
SFC =0.444 L/kWh

16. Another Part of the Problem
Compare this SFC with the SFC that the tractor would obtain if the throttle remained at the full setting, i.e. N = 1
SFC =( /X)*PTM
SFC =( /0.33)*1 = L/kWh
Improvement with reduced throttle setting
% reduction in SFC = 100*( )/0.511 =13%

17. Shift up-throttle back
Vary X
Vary N
X = Equivalent PTO Power required by operation/Rated PTO Power
N = Partial throttle engine speed/full throttle engine speed

18. Brief Introduction to Engines
Engines covered in detail in TSM 464
Four-stroke engine
Intake
Compression
Power
Exhaust

19. Engines Many types & sizes of IC engines
Most common type of tractor engine has vertical cylinders arranged side by side or in line
V engines have been used as well

20. Engine Structure

21. Engine Example: John Deere
Diesel, Industrial, Power Tech Series, 6068T, 185 HP
Identify components?
Turbocharger
Electric Starter
Oil filter
Alternator
Fan
Fuel filter

22. Tractor Pulling Performance
How effective are tractors in using engine power to pull implements?
Depends on:
Configuration of tractor
2WD vs MFWD vs 4WD vs Track
Firmness of ground
Soft vs firm vs concrete
Can be described by Tractive Efficiency

23. Tractive Efficiencies

24. Power Flow from Fuel to Soil40
COMBUSTION 32 80
GROSS FLYWHEEL
Percentages 92
25-26
NET FLYWHEEL
77-80 91
82-85
84-88 99
89-91
TRANSMISSION INPUT
Tractive Efficiency
tractor type
conc
Firm
Tilled
Soft 87 72 67 55
2WD 76 64
MFWD 88 77 75 70
4WD 74
Track
85-90
90-92
AXLE
PTO 96
See table
DRAWBAR

25. Example Problem
A farmer has a 6 m wide offset disk harrow that he uses for primary tillage. This harrow requires a drawbar pull force of 46 kN while traveling in the field at 8 km/h on average. Assuming that a MFWD (mechanical front wheel drive) tractor will be used to pull the implement and that the soil condition is firm on average, calculate the following:
Drawbar power,
Equivalent PTO power for tractor to be able to pull implement at the given speed

26. Example Problem: Solution
Given:
Drawbar force=46 kN
Speed=8 km/h
Tractor: MFWD and soil is firm
(a) Pdb=Drawbar force x travel speed
Pdb=46 [kN] x 8 [km/h] x 1000/3600 kW
Pdb= 102 kW
(b) etractive= Pdb /PPTO
PPTO= Pdb / etractive
PPTO=102/0.76=134 kW
Equivalent PTO power required is 134 kW to pull this implement
For a given implement, how do we determine the drawbar pull?