CASE STUDY:- A Thermodynamic Analysis Of A Tractor EngineFor Use In India With Given Engine Performance Targets.

CASE STUDY:-  A Thermodynamic Analysis Of A Tractor Engine For Use In India With Given Engine Performance Targets.

A Brief Literature Review:

A tractor is an engineered vehicle specifically designed to deliver Power and traction/tractive effort to haul heavy equipments like agricultural and construction equipments.

  • The first "semi portable" engine for farm purpose was designed by Richard Trevithick 1812 which was meant for agricultural purpose. It was known as "Barn Engine". It was used to drive a threshing machine.
  • The first portable engine was designed by William Tuxford of Boston. He started manufacturing of engine which was built around a locomotive-style boiler with horizontal smoke tubes.A large flywheel was mounted on the crankshaft, and leather belt was used to transfer the drive to the equipment being driven.
  • In 1850, john Fowler used a Clayton & Shuttleworth portable engine to drive apparatus in the first public demonstrations of the application of cable haulage to cultivation.
  • In parallel with the early portable engine development, many engineers attempted to make them self-propelled – the fore-runners of the tractor engines. In most cases this was achieved by fitting a sprocket on the end of the crankshaft, and running a chain from this to a larger sprocket on the rear axle. These experiments met with mixed success.
  • The first proper tractor engine, in the form recognisable today, was developed in 1859 when British engineer Thomas Aveling. He modified a Clayton and Shuttleworth engine, which had to be hauled from job to job by horses, into a self-propelled one. The alteration was made by fitting a long driving chain between the crankshaft and the rear axle.

Available Tractor Configurations:

Tractors can be generally classified by number of axles or wheels with main categories:-

  • 2-wheel tractor/single-axle tractors. 
  • 4-wheel tractors (two-axle tractors). Among four-wheel tractors (two-axle tractors), most are two wheel drive(usually at the rear); but many are two-wheel drive with front wheel assist, four wheel drive (often with articulated steering), or track tractors (with steel or rubber tracks).

Tractor Market In India:

Indian is one of the largest producers of tractors in the world, manufacturing around 660,000 units per year. The main centers of tractor production are in the states of Karnataka, Maharashtra, Tamil Nadu and Gujarat, and the top domestic markets are in Maharashtra, Punjab, Haryana, Uttar Pradesh, Madhya Pradesh, and Andhra Pradesh. Indian tractors are also exported to other countries in Asia, Africa, Europe, and America.

Types And Uses Of Tractors In India:

  • The most commonly used tractors in Indian are four-wheeled, 31 HP to 40 HP tractors. These can be put to multiple agricultural uses, and, aside from their price, this is the main consideration that farmers make in their purchase. Aside from their use in farms, orchards, and gardens, these tractors can also be used to haul produce, goods, equipment, and any other loads from one destination to another.
  • Tractors are also used in construction activities, in garbage collection, and in many other non-agricultural activities.
  • Higher horsepower tractors between 41 HP and 50 HP are also a growing market segment in India, but, with their very expensive pricing, they are mainly employed on larger farms.

Current Scenerio:

Indian farmers have become more aware of the benefits of farm mechanization and the role of the tractor in reducing farm labour drudgery, making multiple crops possible in a single year, speeding up farm operations, and reducing overall farm expenses.

Government funding and subsidies, as well as the availability of nearly 95% credit from commercial banks, state land development banks, regional rural banks, and other financial institutions, have made it possible for a growing number of farmers with small-sized and medium-sized landholdings to purchase tractors. With the problem of rising labour scarcity due to increased migration to urban areas, better work opportunities in other sectors, and government employment schemes, having a tractor has become more or less of a necessity for many farmers. Without it, they wouldn’t have sufficient manpower to complete all the essential farming tasks.

Tractor Engine Models [In GT-Power]:

#CASE -1: 4-Cylinder Naturally Aspirated 4-Stroke Engine With SOHC.

 

ENGINE MODEL DESCRIPTION/CONFIGURATION:

  • 4-cylinder, naturally aspirated, 4-strokes engine with SOHC( single over head cam shaft).
  • Ambient inlet conditions: Pressure = 1bar, Temperature = 300K.

Cylinder Geometry:   

  • Bore = 100 mm.
  • Stroke = 100 mm.
  • Connecting Rod = 200 mm.
  • TDC Clearance height = 0.5 mm.
  • Compression Ratio = 17.0

Combustion Model:

  • Non-Predictive combustion model (DI WIEBE)
  • 2-zone combustion (temperature) methodology used instead of 1-zone combustion (temperature) methodology. 

 

Non-Predictive Combustion Model (DI WIEBE)

  • The non predictive combustion model used is  DI WIEBE
  • Direct injection diesel Wiebe model.
  • In this model, heat input is taken as constant not affected by any other external measures like rail pressure, injected fuel mass..etc. It uses "3-term Wiebe" functions.These Wiebe curves approximates the "typical" shape of DI compression ignition, single main injection burn rate.
  • The purpose of using "3-term Wiebe" function is to model the pre-mix and diffusion portion of the combustion process.

 

 

Heat Transfer Model: Woschni GT.

Engine Performance Targets:

  • Power = 75 hp @2200 rpm (Rated RPM).
  • Max torque  = 20% more than rated Torque.
  • BSFC targets = min 210g/KWh    max 225g/KWh.
  • Consider rated A/F ratio as 25 and intermediate A/F ratio as 22.
  • Consider rated speed as 2200 rpm and intermediate speed as 1300 rpm

Results (Plots) #Case:1

 

Cylinder Result Data:

Variable Unit cylinder-1 cylinder-2 cylinder-3 cylinder-4
Burned Mass Percent at Combustion Start(EGR+Resid) % 7.859 7.936 8.851 30.06
Effective Fuel-Air Ratio at EVO NoUnit 0.04546 0.04546 0.04546 0.04546
IMEP720 - Net Indicated Mean Effective Pressure bar 5.460 5.283 5.080 0.8383
Indicated Efficiency % 34.21 34.00 33.71 9.203
Maximum Pressure bar 43.67 42.38 41.81 36.70
Volumetric Efficiency (Manifold), Air fraction 0.7047 0.6860 0.6652 0.4019

Engine Result Data:-

Variable Unit Value
Engine Speed (cycle average) RPM 1300
IMEP720 - Net Indicated Mean Effective Pressure bar 4.165
BMEP - Brake Mean Effective Pressure bar 3.153
Volumetric Efficiency, Air fraction 0.6145
Volumetric Efficiency (Manifold), Air fraction 0.6145

 

 

 

Observations:

  • From the results, it is clear that power is down by (-76%) from the target value for the max power condition and also  for the max torque condition the power is less than by (-24%) from the max. power conditions.
  • The torque achieved for max. torque condition at which the tractor has to be designed is (+29%) higher  tthan the rated torque.
  • BSFC is 443.6g/KWh which is (+111.23%) higher than than min. target value and (101.36%)  higher than the max. terget BSFC for rated rpm.
  • Whereas, for "Max Torque Condition" BSFC is 369g/KWh which is (+68%) higher than the required target value.

From the above simulation we can say that in order to achieve above mention targets with the following constrains, this engine configuration is not good enough to meet the required targets.

 

#CASE -2: 4-Cylinder Turbocharged 4-Stroke Engine with Intercooler. 

ENGINE MODEL DESCRIPTION/CONFIGURATION:

  • 4-cylinder, turbocharged, 4-strokes engine with DOHC( Double over head cam shaft).
  • Ambient inlet conditions: Pressure = 1bar, Temperature = 300K.

#CASE 2.1:

Compressor Outlet Condition:

  • Pressure =2.4 bar
  • Temperature = 500K

Cylinder Geometry:   

  • Bore = 100 mm.
  • Stroke = 100 mm.
  • Connecting Rod = 200 mm.
  • TDC Clearance height = 1 mm.
  • Compression Ratio = 17.0

Heat Transfer Model: Woschni GT.

Combustion Model:

  • Non-Predictive combustion model (DI WIEBE)
  • 2-zone combustion (temperature) methodology used instead of 1-zone combustion (temperature) methodology (similar as above).

 

 

Engine Performance Targets:

  • Power = 75 hp @2200 rpm (Rated RPM).
  • Max torque  = 20% more than rated Torque.
  • BSFC targets = min 210g/KWh    max 225g/KWh.
  • Consider rated A/F ratio as 25 and intermediate A/F ratio as 22.
  • Consider rated speed as 2200 rpm and intermediate speed as 1300 rpm

Results (Plots)#case2.1:

Cylinder result data:

Variable Unit cylinder-1 cylinder-2 cylinder-3 cylinder-4
Burned Mass Percent at Combustion Start(EGR+Resid) % 4.696 4.874 4.634 4.573
Effective Fuel-Air Ratio at EVO NoUnit 0.04545 0.04545 0.04545 0.04545
IMEP720 - Net Indicated Mean Effective Pressure bar 15.58 15.55 15.71 15.81
Indicated Efficiency % 40.30 40.26 40.34 40.38
Maximum Pressure bar 114.6 114.7 115.1 115.6
Volumetric Efficiency (Manifold), Air fraction 1.707 1.705 1.719 1.730

Engine Result data:

Variable Unit Value
Engine Speed (cycle average) RPM 1300
IMEP720 - Net Indicated Mean Effective Pressure bar 15.66
BMEP - Brake Mean Effective Pressure bar 14.28
Volumetric Efficiency, Air fraction 1.715
Volumetric Efficiency (Manifold), Air fraction 1.715

#CASE 2.2

Compressor Outlet Condition:

  • Pressure =2.4 bar
  • Temperature = 500K

Downsizing The Engine 

Cylinder Geometry:   

  • Bore = 86 mm.
  • Stroke = 86 mm.
  • Connecting Rod = 129 mm.
  • TDC Clearance height = 1 mm.
  • Compression Ratio = 17.0

Heat Transfer Model: Woschni GT.

Combustion Model:

  • Non-Predictive combustion model (DI WIEBE)
  • 2-zone combustion (temperature) methodology used instead of 1-zone combustion (temperature) methodology (similar as above).
  • The DI WIEBE combustion graph showing the "Burn Rate vs Crank Angle" for the given engine model.

Results (Plots)#case2.2:

Cylinder result data:

Variable Unit cylinder-1 cylinder-2 cylinder-3 cylinder-4
Burned Mass Percent at Combustion Start(EGR+Resid) % 1.281 1.658 1.538 24.46
Effective Fuel-Air Ratio at EVO NoUnit 0.04546 0.04545 0.04545 0.04546
IMEP720 - Net Indicated Mean Effective Pressure bar 21.87 21.06 21.32 7.526
Indicated Efficiency % 41.42 41.41 41.50 24.90
Maximum Pressure bar 150.5 144.2 145.2 127.2
Volumetric Efficiency (Manifold), Air fraction 2.368 2.269 2.296 1.334

Engine result data:

Variable Unit Value
Engine Speed (cycle average) RPM 1300
IMEP720 - Net Indicated Mean Effective Pressure bar 17.94
BMEP - Brake Mean Effective Pressure bar 16.49
Volumetric Efficiency, Air fraction 2.067
Volumetric Efficiency (Manifold), Air fraction 2.067

Observations #case2.1:

  • From the results of "case 2.1" we see that power is up by (+31%) from the target value for the "max power condition". 
  • The torque achieved for max. torque condition at which the tractor has to be designed is (+13%) higher than the rated torque and (+278.2 Nm) more than the previous case (#case 1).
  • BSFC is 231.7g/KWh which is (+10.33%) higher than than min. target value and (+5.31%)  higher than the max. terget BSFC for rated rpm.
  • Whereas, for "Max Torque Condition" BSFC is 227g/KWh which is just (+3.181%) higher than the max target value.

Similarly # case 2.2:

  • we see that power is up by (+17%) from the target value for the max power condition. 
  • The torque achieved for max. torque condition at which the tractor has to be designed is (+9.5%) higher than the rated torque and (+233 Nm) more than the previous case (#case 1).
  • BSFC is 214g/KWh which is (+1.90%) higher than than min. target value and (-2.72%)  lesser than the max. terget BSFC for rated rpm.
  • Whereas, for "Max Torque Condition" BSFC is 217g/KWh which is  (-1.36%) lesser than the max target value.
  • Apart from that if we compare "case 2.1" and "case2.2", we find that both the power and tractive force is  lower for the case 2.2 as due to downsizing of the engine but it also helped in  improving the BSFC for the same putting it into the permissible target range.

So comparing all the above critical parameters of  the above cases (case1, case 2.1, case2.2), we can say that a 4-cylinder turbo charged engine is suitable for high power/ torque application and with good fuel economy, makes it even more favourable as the cost of fuel plays an important role in sustainability.

However a downsized turbocharged engine can provide much better fuel economy at relatively moderate tractive power needed for all the heavy hauling and due to smaller size it reduces the overall cost.


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