Effect On The Cooling System Of Increasing Engine Engineering Essay

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The primary job of the cooling system is to keep the engine from overheating [Sk8]. In order to prevent the engine from over heating the engine should be cooled via a direct system. Usually, it consists of one or more radiators, to flow cool water around the engine block [Sk2]. The cooling system also has several other important jobs. The engine runs best at a fairly high temperature. When the engine is cold, it emits more pollution and is less efficient and also engine components wear out faster. So another important job of the cooling system is to allow the engine to heat up as quickly as possible, and then to keep the engine at a constant temperature [Sk8].

This system needs to be lightweight and meet the Formula Student rules [Sk2].

Design constraints

The Formula Student rules strictly specifies for the cooling system to only use plain water or water with a maximum volume ratio of 0.015:1 rust inhibitor. Antifreeze or other glycol-based fluids are not allowed [Sk1].

The required functioning heat for the Yamaha YZF-R6 engine is 860C. The recommended coolant volume is equals to 2.15 liters [Sk3].

Background research

The engine runs best when its coolant is about 200 degrees Fahrenheit (860 degrees Celsius) [Sk9]. It's at this regulated temperature that the engine is the most efficient mechanically and thermodynamically [Sk2]. The combustion chamber is hot enough to completely vaporize the fuel, providing better combustion and reducing emissions. At this temperature the oil used to lubricate the engine has a lower viscosity (it is thinner), so the engine parts move more freely and the engine wastes less power moving its own components around and Metal parts wear less [Sk9]. The heat generated by the combustion increases the engine's temperature, and the cooling system gathers this heat and sends it out in the surrounding environment [Sk2].

The ducts are containing the cooling fluid; they are the links between the engine and the radiator [Sk2].

Figure 1: Engine Cooling Components [Sk6]

To achieve the Engine cooling efficiently the cooling system is composed of

A cooling path casted within the engine

A water pump

A heat exchanger (Radiator)

A thermostat

A pressure valve

A fan

And ducts [Sk2]

Figure 2: Coolant Flow & Pumping [Sk10]

Cooling path casted within the engine

­­The cooling system of an engine has a lot of plumbing [Sk10]. The cooling path is casted within the engine and designed to run along the cylinder liners to collect the combustion heat and even the temperature in the engine [Sk2]. The pump sends the fluid into the engine block, where it makes its way through passages in the engine around the cylinders, and then it returns through the cylinder head of the engine. The thermostat is located where the fluid leaves the engine; the plumbing around the thermostat sends the fluid back to the pump directly if the thermostat is closed and If it is open, the fluid goes through the radiator first and then back to the pump [Sk10].The water pump is actuated by the engine; it is designed to circulate the cooling fluid in the entire cooling system. The heat exchanger (or radiator) realizes a heat transfer between two different environments (The cooling water and the external air) [Sk2]. There is also a separate circuit for the heating the system. This circuit takes fluid from the cylinder head and passes it through a heater core and then back to the pump [Sk10].

Thermostat

The thermostat is simply a valve that measures the temperature of the coolant and, it regulates the engine temperature by allowing or not allowing the cooling fluid to pass into the radiator. If coolant is hot enough, the thermostat opens to allow the coolant to flow through the radiator [Sk6].

Figure 3: Thermostats [Sk6]

­­The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the radiator [Sk12]. At low temperatures, the outlet to the radiator is completely blocked [Sk12] (The bypass system allows the coolant to keep moving through the engine to balance the temperature and avoid hot spots, because flow to the radiator is blocked, the engine will reach operating temperature sooner and, on a cold day, will allow the heater to begin supplying hot air to the interior more quickly [Sk6].) all of the coolant is re-circulated back through the engine. Once the temperature of the coolant rises to 180 and 195 F (82 - 91 C), the thermostat starts to open, allowing fluid to flow through the radiator. By the time the coolant reaches 200 to 218 F (93 - 103 C), the thermostat is open all the way [Sk12].

Figure 4: Open & Closed position of a Thermostat [Sk12]

The heart of a thermostat is a sealed copper cup that contains wax and a metal pellet.  As the thermostat heats up, the hot wax expands, (begins to melt at around 180 F, different thermostats open at different temperatures, but 180 F is a common one [Sk12].) pushing a piston against spring pressure to open the valve and allow coolant to circulate [Sk6].

Since the 1970s, thermostats have been calibrated to keep the temperature of the coolant above 192 to 195 degrees.  Prior to that, 180 degree thermostats were the norm.  It was found that if the engine is allowed to run at these hotter temperatures, emissions are reduced, moisture condensation inside the engine is quickly burned off extending engine life, and combustion is more complete which improves fuel economy [Sk6].

The thermostat is usually located in the front, top part of the engine in a water outlet housing that also serves as the connection point for the upper radiator hose.  The thermostat housing attaches to the engine, usually with two bolts and a gasket to seal it against leaks.  The gasket is usually made of a heavy paper or a rubber O ring is used.  In some applications, there is no gasket or rubber seal.  Instead, a thin bead of special silicone sealer is squeezed from a tube to form a seal [Sk6].

The cooling system uses pressure to further raise the boiling point of the coolant. The boiling temperature of coolant is higher if system is pressurized. Most cars have a pressure limit of 14 to 15 pounds per square inch (psi), which raises the boiling point another 450 F (250 C) so the coolant can withstand the high temperatures [Sk11]. The pressure valve is fitted on top of the radiator where an air pocket is constantly present. It regulates the pressure in the system by releasing air. The fan is fitted against the radiator. It provides an extra air flow when the radiator can't dissipate the required heat (i.e. stationary vehicle) [Sk2].

The radiator cap actually increases the boiling point of the coolant by about 450 F (250 C). The cap is actually a pressure release valve, and on cars it is usually set to 15 psi [11]. The boiling point of water increases when the water is placed under pressure [Sk11].

Figure 5: Pressure Cap [Sk11]

When the fluid in the cooling system heats up, it expands, causing the pressure to build up. The cap is the only place where this pressure can escape, so the setting of the spring on the cap determines the maximum pressure in the cooling system. When the pressure reaches 15 psi, the pressure pushes the valve open, allowing coolant to escape from the cooling system. This coolant flows through the overflow tube into the bottom of the overflow tank and the arrangement keeps air out of the system. When the radiator cools back down, a vacuum is created in the cooling system that pulls open another spring loaded valve, sucking water back in from the bottom of the overflow tank to replace the water that was expelled [Sk11].

Effect on the Cooling System of Increasing Engine Horsepower

It's helpful to understand that, during operation, internal combustion engines convert the energy of fuel into mechanical work and heat. Approximately one-third of the fuel energy goes into the mechanical work of the moving vehicle, one-third into exhaust heat, and one-third into heat transferred by the engine cooling system to the ambient air [Sk5].

Equation 1 [Sk5]

This means that heat load to the cooling system at rated power is proximately equal to the rated power of the engine expressed in BTUs per minute (HP X 42.4 = BTU/minute). From this we can see that if an engine is modified to increase its horsepower, the load to the cooling system will also increase. In fact, the heat load to the cooling system will increase by about the same percentage as the increase in engine horsepower [Sk5].

Heat Load to the cooling system

The heat load to the cooling system is related to the flow through the radiator and the temperature drop through the radiator by the following expression:

Equation 2 [Sk5]

Where is the heat load BTU/min., is the mass flow rate of the coolant in BTU per pound per degree C, is the temperature drop through the radiator in degrees C, and is specific heat of the coolant.

For a given heat load and coolant flow rate, the coolant temperature drop through the radiator will be constant, and nothing can be done to the design of radiator that can change temperature drop. Adding rows or fins or face area or whatever will not change the temperature drop through the radiator [Sk5].

Temperature Differential

In the cooling system heat transfer is governed by a single major factor-the heat load to the cooling system.  Under "steady-state" conditions, the heat load to the cooling system will be transferred to the cooling air by the radiator no matter how good or how poor the radiator [Sk5].

The difference between the radiator average core temperature and the temperature of the cooling air is the driving force behind the transfer of heat from the coolant to the cooling air.  When an engine starts and is run up to rated load, the coolant begins to heat up. Initially, the coolant and metal in the engine absorb the heat being produced and continue to do so until the temperature of these parts exceeds the cooling air temperature.  At this point, heat transfer to the cooling air commences.  The coolant temperature continues to rise until it reaches a temperature at which the difference between the radiator average core temperature and the incoming cooling air is great enough to transfer the entire heat load to the air. This then becomes a "steady-state" condition [Sk5].

BMM 6 Design

The selection of the radiator would be based on its availability and its cooling efficiency. The cooling efficiency depends directly on the surface in contact with the air.

Figure 6: Cooling Hoses & Connectors [Sk4]

There are currently two different radiators available in the workshop. The first one is the standard Yamaha YZF-R6 2005 radiator (Figure 7). It has a curved shape to fit in the bike package while providing the correct amount of cooling. The R6 radiator core dimensions are 320mm x 258mm x 24mm (width x height x depth) [Sk3].

Figure 7: Standard R6 2005 [Sk2]

The second one is made by Titan-lite Motorsport based in the West Midlands (Figure 8) This company is well known in the motorsport world to produce radiator and oil coolers. This radiator has a flat shape unlike the standard one. The Titan-lite radiator core dimensions are 265mm x 200mm x 24mm (width x height x depth)

Figure 8: Titan-lite Radiator [Sk2]

The following table is a set of data collected from last year's analysis [Sk2].

Radiator

Weight

(kg)

Coolant

(litres)

Coolant weight

(kg)

Total weight

(kg)

Standard R6

1.3

0.75

0.75

2.05

Titan-lite

1.3

0.4

0.4

1.7

To evaluate the efficiency a calculation to determine the core's density is made. The standard R6 has a core volume of 1.98 litres. Assuming that all the coolant volume is situated in the core we can say that the density factor is

Equation 3 [Sk2]

Equation 4 [Sk2]

The Titan-lite has a core volume of 1.27 liters. Using the same assumption as above the density factor is

Equation 5 [Sk2]

The Titan-lite radiator has a less dense core in terms of cooling fluid. This means that more fins can be added around the tubes to provide more heat exchange surface. Based on this assumption the Titan-lite radiator is bound to offer a better cooling over the standard R6 radiator. Although, using a test rig to compare both radiators would give practical results regarding their cooling efficiency [Sk2].

The radiator is placed on the right hand side of the car. The right side-pod will accommodate the heat exchanger and provide the required air mass flow. Right side placing provides the shortest inlet of the coolant to the pump. The exact location is defined by the side-pod responsible team member depending on his flow calculations.

The FAN

The fan used in BM-6 is carried over BM-5's design which has a 9inch (225mm) fan diameter. The fan technology is a 'pull fan' that is placed behind the radiator and 'pulls' the air through it.

Figure 9: Fan [Sk2]

This fan position allows a less turbulent air flow to come into the radiator which provides a good heat exchange with the fins. The downside is that the fan will work in hot air (low density) so to pull cold air in the radiator it will need give out a higher air mass flow rate compared to what is required at the radiator [Sk2].

Hoses

The hoses used to transfer the coolant from the engine to the radiator need to be selected carefully. Their length, internal diameter and geometry (curvature) will introduce pressure loss in the cooling system. This pressure loss will be reflected on the water pump and indirectly on the engine. The engine needs to maintain its efficiency as high as possible.

Budget

Item

Type

Unit Cost

Quantity

Source Detail

Cooling Path Casted within Engine

Casting Process

£ 00.00

 

Present within engine

Water Pump

Part

£ 00.00

 

Present within engine

Thermostat

Part

£ 00.00

 

Present within engine

Ducts/Hoses

Parts

£ 70.00

2

 

Fan

Part

£ 145.00

1

 

Filler Neck

Part

£ 80.00

1

 

Radiator

Part

£ 250.00

1

 

Welding

Process

£ 30.00

2 Hours

 

Fan Switches/ Thermostatic kit

Parts

£100.00

 

 

Hose connectors/Clips/Cap/fittings

Part Fittings

£ 110.00

22

 

These are the parts essential for the complete cooling system as per our team's requirements.

Part List [Sk4]

S. No.

Part name

quantity

S. No.

Part name

quantity

Radiator

14

Water jacket joint

1

1

Coolant Reservoir Hose

1

15

Water Pump Outlet Pipe

1

2

Throttle Body Hose

2

16

Water Pump Inlet Hose

1

3

Radiator Outlet Hose

1

Thermostat

4

Radiator Inlet Hose

1

4

Radiator Inlet Hose

1

5

Oil cooler Outlet Hose

1

17

Water Pump Outlet Hose

1

6

Thermo Switch Coupler

1

18

Carburetor outlet Hose

1

7

Radiator Fan Motor Coupler

1

19

Thermostat cover

1

8

Radiator

1

20

Thermostat

1

9

Radiator Fan

1

Water Pump

Oil Cooler

16

Water Pump Inlet Hose

1

5

Oil cooler Outlet Hose

1

17

Water Pump Outlet Hose

1

10

Bolt

1

21

Water Pump Hose

1

11

Washer

1

22

Clutch Wire and Holder

1

12

Oil Cooler

1

23

Water Pump

1

13

Oil Cooler Inlet Hose

1

Few Rules to be kept in Mind while designing cooling system will help.

Anything you can do to increase the coolant flow rate, within limits described, will improve heat transfer and cooling performance [Sk5]. Anything you do to restrict or reduce the coolant flow rate will hurt cooling performance [Sk5].

Anything you can do to improve airflow through the radiator core will help [Sk5].  Anything that blocks or slows airflow, either before or after the radiator, will hurt [Sk5].

Increasing the face area of the radiator by making the radiator larger will help [Sk5].  Relocating other heat exchangers that were in front of the radiator in order to expose more radiator face area to ambient cooling air will also help [Sk5].

Increasing the fin count may help, but it may hurt [Sk5].  Increasing the count above 16 fins per inch will almost always hurt [Sk5].

A plate fin radiator and a serpentine fin radiator of the same fin count, tube size, tube rows, face area, core depth, etc., will have the same heat transfer performance [Sk5].  However, serpentine fin radiators can be made with higher fin counts, sometimes resulting in improved performance [Sk5].

Louvered fins provide greatly improved heat transfer with some increase in cooling air restriction [Sk5].  Changing from a non-louvered radiator to a louvered radiator core almost always improves heat transfer performance [Sk5].

Adding a row of tubes may help, but it may hurt by increasing cooling air restriction and reducing the coolant flow rate in the tubes [Sk5].  If the cooling airflow has been increased over the original installation, adding a row or two will probably help in this situation. Increasing the number of rows beyond 4 in a louvered fin core will almost always hurt [Sk5].

Adding two rows of tubes without increasing the coolant flow rate (Bigger pump or turning the old pump faster) will probably reduce performance because of low coolant flow rate in the tubes [Sk5].  Reducing the tube size or going to dimple tubes may help [Sk5]. Increasing the coolant flow rate will surely help [Sk5].

For maximum heat transfer performance in warm climates, use water as a coolant with an additive to provide a corrosion inhibitor and water pump lubricant [Sk5].  For winter service, use 50/50 water to ethylene glycol coolant solution that includes corrosion inhibitors and a pump lubricant [Sk5].

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