Valve Timing Graph

This report is written on the disassembly of GX160 stationary engine, the main objective was to study on its working mechanism, materials used in manufacturing and its working efficiency based on the engine design. Therefore in order for all the theoretical knowledge on the working of this engine to be understood well, it had to be done practical through disassembly of the engine. HONDA GX160T1 used as air compressor, lawn mower, Go-Kart, generators, pumps, agricultural equipment and small construction equipment as commercial, individual and household upon the requirement. The HONDA GX160T1 is selected to perform this lab report due to its wide range of use, easy to disassemble and assemble and compact in size. Therefore this will provide a deeper understanding of widely used 4-stroke, single cylinder, air cooled engine and its operation, (Starodetko, et al 2013).

1. Bore (B) = 64.2 mm
2. Stroke (S) = 42 mm

 III. Valve timing graph is attested at the end of the report

1. Valve Diameter (I) Inlet valve stem diameter = 3.2 mm (II) Exhaust valve stem diameter = 3.4 mm
2. Clearance volume (VC) = 20.10cc
3. Gasket thickness = 1.2 mm

VII. Length of con rod (r) = 86.2 mm

1. The displacement capacity can be explained as volume swept by a number of pistons located in an engine.

Mathematically representation is:

          Vd = π *      

 (Area of Piston) * Stroke * Number of Cylinders in the engine

        Vd = Nc (π/4)B2S    2-8  Vd = 147.5 cc  

1. The total combustion chamber volume includes clearance volume also the volume of gasket

VBDC = Vd + Vc  Vc

 (Clearance Volume) = volume of gasket + Combustion volume of cylinder head

 Volume of gasket = (π/4)B2*Thickness of gasket        

         = 4.12 cc

Therefore   

     Vc = 17cc + 4.12 cc       

       = 21.12 cc     

    VBDC = Vd + Vc             

      = 151.62cc

III. Compression ratio is the ratio of volume of combustion chamber of largest to smallest.

RC = (Vc + Vd) / Vc    2-12  

 = 151.62/21.12   

 = 7.18  

1. Ratio of conrod length to the crank offset

 R = r/a     2-6  Where

 r = Length of control = 88.1 mm

 a = Crank offset = Stroke / 2 = 21.5 mm   

R = 88.1 mm / 21.5 mm      

 = 4.09   

It is the ratio of bore over stroke; it is 1.53 in our engine. This is termed as an Over square engine. For a square engine the B/S is equal to 1 and for under square engine. The B/S is less than 1. Over square engines have typically less stroke length compared to bore, thereby the movement of the piston from TDC to BDC is less and affecting the friction. In our engine’s case, due to the less stroke length the friction is very low compared with a squared or under square engines, where stroke length is equal or more than the bore length, (Starodetko, et al 2013). 

Con Rod Length and Compression Ratio

I believe the commercial application of the Honda GX160T1 is more in the market due to adaptability for applications. This might be one of the factors that Honda decided to design this over square engine. The over square engines are good in developing peak torque at high speeds. If we increase in stoke length, this will result on the stroke ratio, typically also leads in increase of overall width of the engine. Due to its wide range of application all over the world, Honda must have considered this aspect and decided the GX160T1 should be over squared. 

 The mean speed of an engine is denoted by Up and the Maximum speed of the engine is denoted by Up.

 From the ratio of instantaneous speed over the average piston speed we can find the value of

     Maximum speed of the engine     = (π/2)*sinθ*[1 + {cosθ/(Sqrt(R2 – sin2θ))}]       2-5   

                                                                     W.Pulkrabek, 2004)

 Where, the average piston speed  

?p = 2SN                                                      2-2 (W.Pulkrabek, 2004)

S = stroke

 N= Rpm of engine  

Rating 1: 4kW at N = 4000 rpm   

?p = 2*0.043m *             

 = 5.73 m/s 

Rating 2: 11N-m at N = 2500 rpm

?p = 2*0.043m *                   

 = 3.6 m/s 

Now, to find out the maximum speed of engine we need to find the crank angle (θ), or the ratio of instantaneous speed to average speed of piston. R for the small engines has values of 3 to 4 Since our engine is small and compact we will consider R = 3 and find the instantaneous speed to average speed ratio in order to determine the Maximum speed of engine. The ratio can be found from Figure 2-2 from textbook a page number 41. The ratio seems to be roughly around 1.66 at crank angle of 70 (θ). We are considering the maximum ratio value from the figure 2-2 in order to determine maximum speed of engine, (Amano, 2010).     

Up/up= 1.66   

Rating 1:    

 4000 rpm at 4kW            

 = 1.66   

Up = 1.66* ?p         

 = 9.5m/s at crank angle

 θ =70 deg Rating 2:     

 2500 rpm at 11 N-m      

 = 1.66   

Up = 1.66 * ?p        

 = 5.98 m/s at crank angle θ =70 deg

Valve stem seal: It helps to distribute the pressure evenly and provide a tight seal for the valve stem. Inlet valve has it.

Mean and Maximum Speed of Engine

According to measurement the value of bore and stroke are respectively 67.4mm and 44.2mm. So it is the over square ratio. Therefore, firstly, this kind ratio can help engine save space. Secondly, it decreases loss of friction during piston working. Thirdly, it has a high compression ratio which is 9.76 (the stand compression is between 8-11). So, it can accelerate mixture gas to combust in combustion chamber. Fourth, with the short stroke, the condor length doesn’t too long so that it can decreases vibration of the piston during movement. Fifth, it has a high speed output, because when the stroke is short, the length from BDC to TDC for piston’s movement will become short, so the times of piston’s reciprocating movements will increase at the unit period time in the cylinder, (Amano, 2010).  

In addition, the output power is high (the output speed is proportional to the output power). So there will be a high output speed.

Another ration of bore to stroke for this 4kw engine is that we can use a turbocharger. The ratio of bore to stroke can be changed according to the actual situation on the premise of not changing the displacement volume. For example, this ratio can be changed to square ratio. Meanwhile, we need to install a turbocharger within inlet manifold and outlet manifold, which utilizes exhaust gases to drive a turbine (located in the exhaust manifold) so that turbine can drive the compressor (located in the inlet manifold), to compress air and send to combustion chamber. Thus, the air compression ratio is increased, and the combustion rate is increased, thereby, it will increase the output power.

Describe the piston and rings, showing your understanding of their function and materials used in their manufacture?

The piston ring is a kind of metal ring, which is embedded inside the piston groove. There are two kinds of rings according its function. They are the compression ring and the oil ring. It is a kind of metal elastic ring with outwardly expanding deformation.

There are three main kinds of functions of piston ring including Functions include: sealing, adjusting oil between cylinder and crankcase, heat conduction for piston, providing oil to the piston and cylinder for lubrication. The first function is that piston ring seals the combustion chamber, preventing the gas in combustion chamber from leaking so that there is enough pressure in it. The second one is that piston ring stops the oil from moving into combustion chamber. The third one is that the ring absorbs the heat that generated by piston to help piston radiation. The last one is that the oil from crankcase is used to lubricate the piston and the inner wall of the cylinder via the oil ring.

Functions of Components

The piston is a reciprocating mechanism in the cylinder. The main function of the piston is to withstand the combustion pressure in the cylinder and transmit this force to the crankshaft through the piston pin and connecting rod. In addition, the piston is also a component of the combustion chamber, (Amano, 2010). 

 Pistons are commonly made of a cast aluminum alloy for excellent and lightweight thermal conductivity. Thermal conductivity is the ability of a material to conduct and transfer heat. Aluminum expands when heated and proper clearance must be provided to maintain free piston movement in the cylinder bore. Insufficient clearance can cause the piston to seize in the cylinder. Excessive clearance can cause a loss of compression and an increase in piston noise.

Piston rings are commonly made from cast iron. Cast iron retains the integrity of its original shape under heat, load, and other dynamic forces. Piston rings seal the combustion chamber, conduct heat from the piston to the cylinder wall, and return oil to the crankcase. Piston ring size and configuration vary depending on engine design

These engines are rated at 4 kw at 4000 rmp and 11Nm at 2500 rmp. Explain why these figures are quoted at different RPM.

figure: 1

As the question show, 4kw means the rated power. 11NM means the maximum torque. When engine works at a low speed, the inlet valve open for a long time, at the same time, the piston moves slowly so engine cannot generate enough power to work fast. At the same time, the torque is also small. However, both torque and engine speed increase as the power increases during the low speed stage. As the engine speed continues to increase, the torque will reach the maximum value. But, the power has not reached the rated one (as shown in figure 1). When engine works at high speed, the high work speed (N) affects the volume of air that goes into the combustion chamber. Therefore, it decreases the torque. Another reason, when the power keeps same during work, the engine speed is inversely proportional to the torque as the equation show, Thereby, the speed at which rated power occurs is faster than the speed at which maximum torque occurs.

1. Describe, with drawing if necessary, how the governor system works. Why do you think this engine has such a governor?

The governator system works as a speed control system in the engine. The governator keeps the speed of the engine in control while adjusting on the amount of pressure or workload on the engine .the running of the engine could be control manually; the governator detects slight changes in speed adjustment and keep it in control, (Starodetko, et al 2013).

Piston and Piston Ring Material

The type of gubernator used in vehicle engines are always mechanical- hydraulic ,the load limiting type of a governator limits the fuel passage (regulates the fuel being pumped into the engine)to ensure that the fuel isn’t loaded in excess, it’s important to note that all this type of governators can perform the same work simultaneously .

FIG.2 cut view of a governator

Mechanical hydraulic type governator operates on the same principle  of any mechanical and hydraulic governator.the Woodward speed governator in the engine operates the fuel racks in order to ensure that the speed is constant, as highlighted earlier its oil supply comes from the engine lubricating system, hence loss of lube oil pressure will results in break in oil supply to the governor hence cause the governator to shut down the engine ,a built in device which works hand in hand with the governator causes the engine to shut down when there is no lubrication of oil pressure,( Lewis and Travare, 2011).  

The governator controls the fuel rack position through use of hydraulic piston and a set of mechanical flyweights, which are driven by the engine shafts located in the lower part of the engine. When the engine speeds the flyweights up and down, the weights of the piston moves in and out, the movements of this flyweights is due to the change of engine speed, which causes the move of the piston in the governator hydraulic system, this movement causes the movement of hydraulic fluid to a large hydraulic piston which is directly linked to the fuel rack. This motion increases or decreases the fuel depending on the speed of the engine.

As the engine operates simultaneously with the governator, oil is also supplied to the governator pump gears, these gears raise the oil pressure to a certain regulated value, and the value level is determined by the spring relief valve. Under all this condition of operation the specific amount of oil and fuel is duly maintained.

FIG.3 illustration of the working of the governator parts use of governator in engines

diesel engine speed is controlled only by the amount of fuel injected into the engine ,diesel engine does not have the capability of fuel limiting by itself, therefore it does not only require means of changing engine speed but also a means of maintaining a desired speed, hence the governator provides all this means, a governator is a speed sensitive device, hence its capable of maintaining a desired speed by controlling it, all gubernators used in diesel engines controls the engine speed by regulating the quantity of fuel delivered to the cylinders,( Eyabi, 2008).

Purpose of spring loaded lever

Camshaft is used to operate to operate valves, since the valve controls the flow of air they open and close in a controlled sequence of time. the spring loaded lever on the camshaft to assist in decompress or system of opening and closing of valves for intake and exit of gases In the engine, when the shaft is at rest or below the ideal RPM the weight are held by the springs and the decompressed shaft part will contact the exhaust valve for the release of the compression, (Lewis and Travare, 2011). 

Use of valve timing 

Valve timing is used to alter the valve lift-event, this process is usually used to improve on the performance, fuel saving and smoke emissions ,The GX160 stationary engine is designed to perform this process to improve on its efficiency and fuel  control, furthermore it works with the combination with variable valve lift system. Valves within the engine control the flow and release of the gases in and out of the combustion chamber. In order for the combustion engine to generate power there should be intake of air and release of exhaust gases, the opening and closing of air intake are controlled by valves, which are known as intake and exhaust gases respectively. Without variable valve timing the intake and exit of gases would have operated in the same manner at once regardless of the engine RPM speed. Variables valve timing enables the control of the engine at different RPM, hence helps in optimizing the engines performance and also prevents on emissions, (Starodetko, et al 2013).

Aspect of the engine

When it comes to engine manufacturing of small engines Honda designs engines which are fuel efficient ,durable and which are well oiled, furthermore the engine designed to operate in hard conditions ,this aspect of designed has resulted in high demand by the buyers .most of this engine are used for lawn ,water irrigation and also lighting in remote  places ,due to high demand Honda has also designed the engine specifications in order to be more affordable, most of the engines prices range from $500-$700 which is quite affordable considering the quality and durability.

Methods of manufacture

The GX160 stationary engine are designed with air cooling devices, it also has throttle, choke and ignition timing, all this functions can be controlled using the drive wires system. This method is quite different from others because mechanical cabling and wiring of the engines usually attracts rusts with time hence lowers the durability of the device. Unlike other engine devices which are controlled by the movement of the flywheel past ignition coil, Timing in the above engine is controlled by adjusting the current condition and engine speed, this means easier startup, fuel efficiency and high peak power.

Materials used in manufacturing

The GX160 stationary engine is built with high quality materials and purpose made components to ensure durability ,most of the engines comes with a 3 year warranty, it’s also manufactured with environmental friendly .the engine is fitted with exhaust devices which prevents it from emitting smoke.

References

Selvaraj, B., Sridhara, S. N., Indraprakash, G., Senthilkumar, A., & Pangaonkar, A. (2011). Effects of intake port geometry on the performance of an SI engine (No. 2011-32-0506). SAE Technical Paper.

Starodetko, K. E., Simand, S., Drobychevskj, T. B., Belyaev, V. J., Yurchuk, K. N., Vitsiaz, A. A., & Kuzmenkov, D. V. (2013). High Performance Characteristics of a Motorcycle Powered by a Four-Stroke Small 50cc-125cc Engine at the Expense of a Positive Displacement Air Compressor as a Supercharger(No. 2013-32-9015). SAE Technical Paper.

Amano, T. (2010). U.S. Patent Application No. 12/310,797.

Eyabi, P. B. (2008). U.S. Patent Application No. 11/518,980.

Lewis, S., & Travare, P. S. (2011). An Alternative Transportation Fuels Update: A Case Study of the Developing E85 Industry (No. SWUTC/11/167360-1). Texas Southern University.