Group 28 - Pressure Washer

Introduction

Group 28 is participating in a product dissection of a gas powered pressure washer for the University at Buffalo’s class MAE 277 taught by Erich Devendorf. The power washer itself is going to be broken down into separate sections allowing two groups to work on it simultaneously. Group 27 is working on the compression unit of the washer while Group 28 works on the engine separately.

Group 27's page can be found here: http://gicl.cs.drexel.edu/wiki/Group_27_-_Pressure_Washer

Having little experience in the field of engineering, the group sees this as a great opportunity to learn how to work together and perform an analysis on a product that is common in our world. By taking the engine apart and thoroughly documenting every part of the process, the group will learn skills required to advance our knowledge of how things work and gain significant engineering experience.

Image of a power washer courtesy of www.Snapon.com

Important

Some of the information that was once on this page has been moved to group 28's alternate page: http://gicl.cs.drexel.edu/wiki/User:MAE277_28_09

Within that page the following can be found: Roles of members, managment proposal, work proposal, causes for corrective action

Initial Product Assessment

1.) Pressure washers are used to clean surfaces of dirt and other debris using a stream of water at high pressure. Surfaces can include buildings, fences, roads and other structures that are not sensitive to high pressure water. For example most cars should not be washed with a pressure washer to avoid damaging the paint.

A wide range of pressure washers are available on the market for home use. These can be used to quickly clean house siding, patios, trailers and other outdoor equipment. Other models are designed for professional use. For example, some washers inject detergents into the water stream which allows users to remove unwanted graffiti. Other commercial uses include cleaning contaminants from air ducts and removing barnacles from the hulls and propellers of ships. The washer that our group has received appears to be for home use.

Pressure washer uses

A pressure washer has several functions. It must intake water from some source. It must also utilize power, in the form of electricity or some type of fuel, to increase the pressure of the incoming water. It then must give the user control over the flow of water. This is done with a hand held nozzle that can be turned on and off.

2.) Pressure washers use a motor which creates rotary motion of a crankshaft. This motor can be either powered electrically or by a fuel. The washer assigned to our group has a motor that runs on gasoline. The motor transforms the chemical energy of the fuel into rotational energy of the crankshaft. This in turn creates linear motion of a piston or plunger which does work on the water to increase its pressure. The high pressure water exits the washer through a nozzle which transforms some of the internal energy into kinetic energy by reducing the cross sectional area of the stream. To summarize, chemical energy of a fuel is converted to rotational energy which is used to do work on the water, increasing its internal energy, through the use of a piston. A fraction of this internal energy is transformed to kinetic energy in the nozzle. The high energy water is used to break up unwanted debris on a surface.

3.) Due to safety restrictions regarding running gasoline engines indoors on campus, we have not been able to run the power washer yet. The engine looks like it would run well; it has obvious signs of use such as having some dirt on it. There seems to be no visible problems; it looks like it is in good shape.

If there are any problems they would most likely come from a few main sources. There might not be the correct amount of oil or other fluids in the engine, which would cause overheating and wear. Another probable cause for problems would be the fuses. If a fuse is blown, the engine will not run. A third cause for problems could be any solid buildup in the intake or exhaust or in the tubes feeding the engine. This would cause the engine to not run at full potential if it ran at all.

4.) This product is fairly complex. The engine goes through a fairly complicated process to produce mechanical work. It takes the chemical energy from gasoline, then combusts it, causing a piston to move creating mechanical work to power a driveshaft. However, this process has been around for at least a hundred years and is well known and understood.

There are five main components in the engine:

- The engine block is a few pieces of metal that house all the other components of the engine.

- The piston/valves are where fuel and air is mixed and combusted to produce mechanical work.

- The intake is where the air gets taken from the environment and put into the engine for combustion.

- The exhaust is where the excess gases left over from the reaction in the cylinders exit the engine.

- The driveshaft, which is turned by the movement of the pistons, takes the mechanical work and applies its movement to the run the compressor.

Many of the components are not too complex; the engine block, intake, and exhaust have no moving parts; however the piston/valves undergo a very complex process. The valves allow air and fuel to enter the cylinder and the exhaust to exit. The piston moves back and forth due to the expansion and compression caused by the combustion of the fuel. The driveshaft takes the back and forth movement of the piston and turns it into rotational movement in the driveshaft. These reactions occur very quickly, causing thousands of rotations a minute.

5.) The pressure washer that we are taking apart is composed of a few different materials, most of which are some form of metal to give it a strong and durable frame. The pressure washer is portable and has two rubber wheels. The washer also has a rubber hose to transport the water from the water tank to the nozzle at the end of the hose. The nozzle is made mostly of plastic. The rest of the pressure washer consists of the engine and compression unit which are made of metals which I would assume to be iron, steel, or aluminum. Our group is focusing on the dissection of the engine unit which is held together by steel nuts and bolts. The inside of the engine appears to be made of the same materials as the outside. Since the temperature inside the engine gets fairly high, a material other than metal would be more likely to melt at these temperatures.

6.) If I were the owner of a Snap-On pressure washer I would be happy with what I spent my money on. There are a lot of products available that are not very efficient when it comes to cleaning, but using pressurized water to clean guarantees it to work on almost everything. Not only is the pressure washer very effective but does not require much effort of the operator. The machine runs on anywhere between a 5-15hp engine and shoots a controlled force of water out of its hose that is aimed by the operator. The product does not require any experience or training to use correctly. The only maintenance required is to make sure that the washer has the proper amount of oil and gasoline. The only other thing to make sure of would be to check the hose for any cracks that would weaken the performance.

7.) There are many other cleaning products available, but in most cases a pressure washer will give you the best results and be the most time efficient. Depending on the surface you are looking to clean someone could choose to use abrasive scrubbers with varies soaps, none of which are as effective as a gas power pressure washer. The only disadvantage in using a pressure washer is that they are more expensive than alternative cleaning products. Due to different sizes and engine power, a gas powered pressure washer can range anywhere from $300 to $1000, which is worth it considering how effectively it cleans. The advantages of owning a pressure washer are that you can clean large surfaces, for example removing the mildew off an entire wooden deck in a matter of minutes. Also the only resources you need are gasoline and a water supply. Another advantage is that the design is very sturdy and built to last. The company also offers a lifetime warranty if anything does happen. The only disadvantage of the product is that it is expensive and not something that every household can afford. There are companies that allow you to rent a pressure washer if you are only looking to use it for a short time period.

Disassembly Procedure

This chart below provides a detailed guide to disassembling this power washer engine. To make documenting and reasembling easier, group 28 grouped all of the parts removed with bolts, nuts, and other small parts together with the main part that they came off of. For example the gas tank was removed with two nuts and a bolt so those items were grouped together so that they can be easily identified later.

Step #	Process	Tools Required**	Difficulty Level*	Image of Step
1	Remove the four bolts to detach the compressor from the engine.	10mm wrench	3
2	Remove the four bolts, nuts and washers from the bottom of the frame to detach the engine.	1/2 inch socket wrench	5
3	Remove two bolts from the bottom of the frame to detach the fuel pump.	8mm socket wrench	2
4	Detach the exhaust assembly located above the engine block next to the fuel tank by removing two nuts and washers. Then remove the metal gasket separating the engine and exhaust assembly.	1/2 inch socket wrench	4
5	Remove one wing nut to detach the intake cover. Remove a second wing nut to detach the filter. Next remove one flat head screw, one round head screw and two screw caps. Then slide off the air filter body, throttle body, and carburetor from the screws.	P1 Philips head screw driver; P2 Philips head screw driver; 10mm socket wrench	1
6	Remove two nuts and then one bolt from the underside of the large red gas tank. Then detach the fuel line from the tank.	10mm socket wrench; 5/16 inch wrench	2
7	Remove two bolts from the throttle assembly that is attached to the cylinder block near the intake. Then remove the nut with the rectangular bolt and cotter pin. Then detach the spring to pull off the assembly.	5/16 inch wrench; 10mm wrench; cotter pin puller	2
8	Remove the spark plug near the cylinder block.	13/16 inch spark plug socket wrench	2
9	Remove the electrical wiring connected the starter to the pull start assembly. Then remove the four bolts from the pull start assembly shroud. Remove the pull start assembly to expose the magneto and flywheel. The magneto is press-fit on the flywheel and was not removed for this reason.	5/15 inch wrench	3
10	Remove the electrical wiring and two bolts connected to the engine near the flywheel.	5/16 inch socket wrench	2
11	Remove the four bolts from the metal shroud covering the cylinder block.	5/16 inch socket wrench	2
12	Remove six bolts from the engine block on the side opposite the flywheel. Then pull off the cover to expose the gears.	10mm socket wrench	3
13	Remove two bolts to detach the cooling fins' cover	10mm socket wrench	2
14	Remove four bolts from the top of the cylinder block. Then pull off the top cover to expose the valve assembly. Then remove the metal head gasket.	12mm socket wrench	4
15	To disassemble the valve assembly, start with the intake valve. First remove the nut. Next slide off the spacer nut, then remove the rocker and pull out the push rod. Then detach the cap to remove the spring and valve from the internal screw. Repeat this process for the exhaust valve.	10mm socket wrench	1
16	With the flywheel side of the engine block facing down, pull up on the main cam gear located near the center of the engine block to remove it. Then slide out the inlet and outlet valves located on the inner wall of the engine block near the original position of the cam gear.	N/A	1
17	Remove the two bolts on the piston that lock it to the crankshaft. Then slide out the piston from the cylinder block.	10mm socket wrench	4
18	Some gears remain inside the engine around the crankshaft. They will not be removed due to an uncertainty in being able to reassemble them.	N/A	N/A

'*'A difficulty level of 1 refers to a simple task that can be easily completed with one attempt. A difficulty level of 5 refers to a task that is difficult and may require multiple attempts. The easiest task was unscrewing the wing nuts to remove the air filter which was taken off by hand. The more difficult tasks required a lot of force from the user or were in tight spaces where it is difficult to attain a good position for working. These levels of difficulty would be a 4 or 5. A 2 or 3 implies basic understanding of how the tool being used works and a non-strenuous amount of force.

'**' The tools are mentioned in what order they are used to remove which part in the same section. If a nut and bolt are removed in the process section, and in the tool section it reads: 10mm wrench and 15/16 socket, then the wrench was used to remove a 10mm nut and the bolt was used to remove a 15/16 socket. All fraction measurements imply SAE inches. All numbers reading "mm" are metric. The tools used include a metric and SAE set of 6 point sockets with a 1/4 inch and 3/8inch ratcheting socket wrench, a p2 and p1 Philips head screw driver, a cotter pin puller, and a metric and SAE set of wrenches.

Component Summary

Below are two charts depicting the parts and components associated with a small pressure washer engine. The compressor is not included in this group’s evaluation and can be found in group 27’s wiki page. The crankshaft of this engine powers the compressor. The charts are group into fasteners such as bolts, nuts, and washers and the major engine components follow. Below the charts are a few paragraphs on various major components that are related in either function form or both describing how they were designed to meet their function as well as the reason for the specified material used which can be found in the following charts.

Fasteners

Part #	Head Type	Quantity	Length (in)	Diameter (in)	Material	Coating	Complexity	Manufacturing Process	Image
1	hex washer	12	1/2"	3/16"	steel	zinc	2	cold forged
2	hex washer	4	2 3/8"	1/4”	steel	zinc	2	cold forged
3	hex washer	4	1 5/8”	1/4”	steel	zinc	2	cold forged
4	hex washer	2	1	3/16"	steel	zinc	2	cold forged
5	hex washer	4	7/8	1/4"	steel	zinc	2	cold forged
6	hex washer	2	5/8”	3/16"	steel	zinc	2	cold forged
7	hex washer	6	1 5/16”	1/4”	steel	zinc	2	cold forged
8	T bolt	1	7/8”	3/16”	steel	zinc	2	cold forged
9	flat	1	5/8”	p1 head	steel	zinc	2	cold forged
10	button	1	5/8”	p2 head	steel	zinc	2	cold forged
11	hex washer	1	1 1/4”	3/16"	steel	zinc	2	cold forged
12	lock nut	4	n/a	1/4”	steel	zinc	2	hot forged
13	washer	4	n/a	1/4”	steel	zinc	2	hot forged
14	flange nut	5	n/a	3/16”	steel	zinc	2	hot forged
15	flange nut	1	n/a	1/2”	steel	zinc	2	hot forged
16	hex nut	2	n/a	1/4”	steel	zinc	2	hot forged
17	split lock washer	2	n/a	1/4”	steel	zinc	2	hot forged
18	wing nut	3	n/a	3/16”	steel	n/a	2	hot forged
19	acorn nut	2	n/a	3/16”	stainless steel	zinc	2	hot forged
20	hex nut	2	n/a	3/16”	stainless steel	n/a	2	hot forged
21	spacer hex nut	2	n/a	3/16”	stainless steel	n/a	2	hot forged

Fasteners

The bolts and screws are made out of steel wire rod that is cut and shaped to the appropriate form in a cold forging process. This process can be used because the steel wire is not very hard and can be shaped easily using dies and rollers. The bolts are heated and cooled after their shape is made, to the specified hardness desired. This allows the bolts to obtain the ability to hold pieces of the engine together while under great loading forces which is due to steel’s high tensile strength. The bolts fit into cylindrical holes and are usually attached to a nut on the other side to secure that parts they are holding. The nuts and washers are made from a similar process, but are first heated for hot forging of the steel. This allows them to be cut and threads be tapped in the nuts. The washers are cut and shaped to form the correct size desired. The role of the nuts is to hold the bolt in place and the role of the washer is to distribute the force over a greater area. Wing nuts are designed to allow a hand to tighten and loosen them, where hex nuts usually require a tool. Several of the fasteners are coated with a form of zinc to protect against corrosion. The stainless steel is made with small amounts of chromium to increase resistance to corrosion and can be found in several nuts and bolts in this engine.

Engine Parts

Part #	Name	Quantity	Material	Function	Manufacturing Process	Complexity Rating*	Image
22	Valves	2	Steel	Allows intake of fresh air and release of exhaust fumes from the engine.	Forged-machined	2
23	Pushrod	2	Steel	Transmits motion of the camshaft to the valve springs	Forged-machined	2
24	Springs	2	Steel	Assist in the opening and closing of the valves	Forged-machined	2
25	Rocker arms	2	Steel	Assists in the transmission of the camshaft motion to the opening and closing of the valves	Forged-machined	2
26	Valve cap	1	Steel	Allows intake of fresh air and release of exhaust fumes from the engine.	Forged-machined	2
27	Spring Retainer	2	Steel	Allows intake of fresh air and release of exhaust fumes from the engine.	Forged-machined	2
28	Gasket	1	Layered Steel	Aids in creating an air tight seal within the cylinder.	Machine Pressed	2
29	Exhaust	1	Iron	Assists in the removal of exhaust from the engine	Cast Molded-Machined	5
30	Intake cover	1	Plastic	Prevents large debris from damaging the air filter	Injection Molding	2
31	Air filter	1	Aluminum/Foam	Filters out small debris from the air to improve engine efficiency	Formed-machined	2
32	Air filter base	1	Plastic	Holds the air filter in place	Injection Molding	2
33	Flywheel fan	1	Plastic	Aids in the removal of excess heat from the engine	Injection molding	2
34	Roll pin cage	1	Stainless steel	Connects the pull start to the crankshaft.	Formed-machined	2
35	Fuel Pump	1	Plastic/Rubber	Delivers fuel from the fuel tank to the engine.	Injection Molding	4
36	Throttle body	1	Plastic	Supports the throttle trigger	Injection molding	2
37	Spark plug	1	Ceramic/Steel	Ignites fuel within the cylinder to initiate combustion	Formed	3
38	Ignition wiring	1	Rubber/Copper	Deliver electrical current to the spark plug.	Formed/Die-Cast	1
39	Cylinder head	1	aluminum	Forms the bounding walls of the cylinder	Cast-machined	2
40	Pull start	1	Plastic	Allows users to transmit linear motion of the rope to angular motion of the flywheel.	Injection Molding	3
41	Cylinder Cover	1	Aluminum	Seals cylinder	Cast-machined	2
42	Case cover	1	aluminum	Supports one end of the crankshaft and seals the engine block.	Cast machined	2
43	Dipstick	2	Plastic	Allows users to measure the amount of oil within the engine block.	Injection Molding	2
44	Carburetor	1	Cast iron	Creates the proper mixture of fuel and air for efficient combustion.	Cast-machined	5
45	Camshaft	1	Cast iron	Allows proper timing for the opening and closing of the valves	Cast-machined	3
46	Flywheel	1	Cast iron	Provides rotational inertia on crankshaft to maintain a constant torque output.	Cast-machined	2
47	Crankshaft	1	Cast iron	Delivers rotational kinetic energy to the compressor when it is rotated by the piston.	Cast-machined/Hardened	3
48	Engine block	1	aluminum	Houses the main components of the engine including the pistor and crankshaft.	Cast-machined	3
49	Manifold plate	1	Aluminum	Prevent users from heat dissipated from the engine	Molded-machined	1
50	Gas tank	1	Aluminum	Stores the fuel needed to power the engine	Molded-machined	2
51	Throttle	1	Aluminum	Allows a user to control the power of the engine by altering the flow of fuel.	Molded-machined	3
52	Piston	1	Variable	Transmits energy from combustion to rotation of the crankshaft.	Cast-machined	3
52a	Pin	1	Aluminum	Transmits energy from combustion to rotation of the crankshaft.	Cast-machined	2
52b	Connecting rod	1	Cast iron	Transmits energy from combustion to rotation of the crankshaft.	Cast-machined	2
52c	Connecting rod	1	Cast iron	Transmits energy from combustion to rotation of the crankshaft.	Cast-machined	2
52d	Piston head	1	Cast iron	Transmits energy from combustion to rotation of the crankshaft.	Cast-machined	2

• Complexity rating is on a scale of 1-5 with 5 being the most complex. A part with only one component that has an extremely simple shape and a uniform material is assigned a rating of 1. An example of this would be the manifold cover. A part with multiple components and materials that required several manufacturing processes is assigned a rating of 5. An example of this would be the carburetor. Screws are assigned a two because they are relatively simple but the threading gives it a more complex manufacturing process.

Below is a description of the major componets in greater detail and gow they correlate to one another. Their process of manufacture is further discussed as well as the choice of material.

Valve/pushrod/spring/rocker arm/valve cap/spring retainer These parts make up the pieces of the valve assembly. They are all made of steel because of its durability and strength. The parts have been forged out of steel and shaped or pressed into their forms by machinery. The components are designed to receive force from the rotating camshaft and actuate the valves to allow gases to either escape or enter. Because of this they must be able to be subjected to forces repeatedly under high stress and temperature, which steel is able to do.

Gasket Layered steel allows the gasket to create a seal between two parts of the engine that cannot allow spaces to form between them. Although casting yields fairly precise parts any gaps between mating parts will be nullified if a gasket is placed between them. Steel allows for easy fabrication and when layered in this form will create a tight seal under high pressure and temperatures.

Exhaust Iron is used in the exhaust because it is inexpensive and can be casted easily. The exhaust is designed to allow gases to pass through it in such a way that they do not harm the user either from their heat or direct inhalation. Iron can be molded easily and is very resistant to wear and will continue to function for a long time under abuse.

Intake cover/air filter/filter base The air intake can be made of plastic because its function only deals with allowing air to flow into the engine and nothing strenuous. This allows it to be easily made and connected together with bolts to insure it stays intact during use. The filter itself is made of foam to separate any unwanted particles from the air as it enters the cylinder. flywheel /flywheel fan/roll pin cage/pull start assembly/ignition wiring/spark plug These parts are designed so that they can function together in starting and maintaining the engine. The pull start contains a rip cord with a plastic handle for easy gripping and has the ability to be easily replaced if it breaks. The cord is wrapped around a small clutch spring system that fits onto the roll pin cage which is already attached to the flywheel. The roll pin cage is made of stainless steel to insure it does not corrode as easily and so it is strong as it connects the pull start to the crankshaft and allows the engine to start moving. On the flywheel is cooling fans which need only be made of plastic as they circulate air. The flywheel is constructed as durable and heavy cast iron to insure its continuing function as it is always moving during operation. The flywheel is formed so that it has magnets on it that allow it to induce a current in the ignition wiring. The wiring itself is drawn through dies to the specified diameter and pulled through rubber tubes so it can be attached to the spark plug. The plug is made of insulating ceramic and has steel, bolt like threading, so that it may be securely fastened to the cylinder head.

Throttle body/throttle The throttle body is designed as plastic because it only acts as a support structure for the throttle and choke levers. The throttle is made of a much stronger, lighter, aluminum. The use of aluminum is to allow minimal material usage and to use a material that hold well under tension because of the spring system used in the throttle. engine block/cylinder head/case cover The engine block is made of cast iron because of its strength and resistance to wear under high pressures and heats associated with engines. The engine clearly made in a cast as the lines where the cast was split is visible along the cylinder head’s cooling fins. While cylinder head was cast in the same mold as the engine block in this engine, it may be attached another way in other models. The casing cover is made separately out of cast iron and bolted on to the engine block so that it allows access to the internal mechanism such as the crankshaft and piston connecting rod. The case cover is lined with a rubber gasket to insure that the oil within does not leak out.

Piston/connecting rod/pin/crankshaft/camshaft These parts are designed together as they interact directly with one another. The purpose of using aluminum for the cylinder head is because of its high strength to pressure and temperature and its lightweight composition. The head is attached to the connecting rod with an aluminum pin to allow for smooth rotation and increased strength against pressure from the rod to the head. The connecting rod itself is made from cast iron as it is more capable of transferring to downward force to the crankshaft with reliability. The crankshaft is hardened cast iron and must be constructed in this way as to allow the greatest transfer of linear force to rotational without deformity. The camshaft is also made of hardened cast iron to best withstand the forces applied on it from the internal gears without deformity.

engine block/cylinder head/case cover The engine block is made of aluminum because of its strength, resistance to wear under high pressures and heats associated with engines, and its low weight. The engine looks like it was made in a cast because the lines where the cast was split is visible along the cylinder head’s cooling fins. The engine was then machined to provide holes to secure bolts (which were then tapped) and some parts such as where the cylinder head is attached was made smoother. The cylinder head is cast out of aluminum and then machined so that it could be attached with bolts to the engine block. The casing cover is cast out of aluminum , as the other parts, to keep the weight of the engine down while not compromising strength. It is bolted to the engine block so that it allows access to the internal mechanism such as the crankshaft and piston connecting rod. The case cover is lined with a rubber gasket to insure that the oil within does not leak out.

Design Revisions

This section goes through possible changes that can be made to improve the power washer. The objective is to improve efficiency, power, ease of use, and increased safety standards all within the intitial target range.

1:The cylinder casing on the engine block is covered with ridges to increase the rate of heat dissipation. On this part of the engine there is also an aluminum plate covering part of the casing. It is most likely there to prevent the user from getting burned by the heat generated by the engine. However, due to its location, it hinders engine cooling due to the fact that it covers the ridges in place to dissipate heat. Keeping the engine from overheating is an important process to keep the engine running smoothly. To improve its design, the plate could have holes in it or be changed into some sort of mesh or grate. These changes would make the guard less likely to block heat dissipation while still performing its duty of keeping the user away from the hot cylinder casing.

2:The power washer is currently started by a pull start. A worthwhile change would be to make it start electrically. A pull start motor can be very physically demanding to use, especially if the user is weaker, older, or out of shape. In addition to this, if the motor hasn’t been used recently or has not been well maintained, a pull start motor can be very difficult to start, even with a very able bodied user. An electric starter for the motor would solve these problems. A push of a button would be all that is needed to start the motor. However, the addition of an electric starter would increase cost but overall would not hurt sales, due to the convenience of the electric starter.

3:Pressure washers have a wide range of uses that include indoor applications. These include cleaning cement floors inside a factory or jetting clogged sewers. In these cases, the pressure washer is being used in a confined space that may not have proper air ventilation. If a fresh air supply is not delivered to the engine of the washer, reduced performance and even engine damage can occur. This could be avoided by adding an oxygen sensor to the washing unit that can shutdown the engine when oxygen levels become too low. An oxygen sensor could also improve the safety of the product. Low oxygen levels would indicate a lack of ventilation which could mean that carbon monoxide levels are dangerously high. Users would not have to worry as much about this problem if an oxygen sensor were added to the design. A higher safety measure would be to also add a carbon monoxide sensor as a backup. If these two sensors were added to the product, the price would increase by about $40 depending on the quality of the sensors. The higher total price would seemingly be justified by the added safety features and the decreased chance of engine damage and performance reduction.

Solid Modeled Assembly

due to technical errors models are not yet available online.

For the solid modeled images we chose to model the piston and connecting rod as well as other related parts. The list of the parts that were modeled includes the piston, pin, connecting rod, connecting rod cap, and one of the bolts that connect the cap to the connecting rod. These parts were chosen as they are the main components of an internal combustion engine but also have unique features that not all engines have. An example of these features would be the fin on the connecting rod cap or the angle at which the cap and rod meet. The program that these images were created in was SolidWorks 2008. This program was chosen because it was most readily available to the group and is also the program we were most familiar with.

Engineering Analysis

Objective: The objective of this question is to solve a specific engineering analysis problem based on a chosen failure in our assigned projects. Below an engine has stopped igniting its air-fuel mixture that allow combustion. The cause can be determined by examining the spark plug and the air-fuel mixture as seen below.

Assumptions:

Air contains 21% oxygen molecules*

Air Fuel Ratio (AFR) of 14.7:1

The engine normally runs on 14.7 grams of air and 1 gram of pure octane per cycle

Octane is 114g/mol, formula C_8 H_18*

Oxygen is 32g/mol, formula O_2 *

Cold type NGK BKR7E-11 spark plug1

One cylinder, 4 cycle engine

The ignition system is based on a spark plug, magnetic flywheel, and electrical coil system

Octane rating based on the Research Octane Number (RON) rating system.

AFR_stoich=14.7 is the air to fuel ratio for an ideal, pure octane fuel mixture.*

Governing Formulas:

Air to fuel ratio equation*: AFR=(mass_air)/〖mass〗_fuel

Lambda equation for air fuel mixture*: λ=AFR/(AFR_stoich )

mass_air*.21=mass_oxygen

Various stoichiometric equations

Solution:

AFR=(mass_air)/〖mass〗_fuel =14.7g/1g=14.7

λ=AFR/(AFR_stoich )=14.7/14.7=1

mass_air*.21=mass_oxygen=14.7*.21=3g

3g/(32g/mol)=.094mol of oxygen

(1g/114g)/mol=.0087mol of octane

To make stoicism calculations more simplified, mol of oxygen and octane are dived by .0087 which gives:

Realistic combustion of octane and oxygen resulting fromλ~1 .

C_8 H_18+〖11O〗_2 □(→┴yields ) 〖6CO〗_2+〖9H〗_2 O+CO+C

Complete combustion of octane and oxygen (Ideal):

C_8 H_18+〖12.5O〗_2 □(→┴yields ) 〖8CO〗_2+〖9H〗_2 O

Low air intake combustion Resulting from a λ<1:

〖2C〗_8 H_18+〖9O〗_2 □(→┴yields ) 16C+〖18H〗_2 O

Discussion: While this engine can be malfunctioning from a number of air to fuel ratio related issues, it can be narrowed down by observing the spark plug. The spark plug can act as a window to what is going on in the engine. By removing the spark plug in this scenario, and looking at the tip of the plug, a significant amount of carbon fouling can be seen causing the engine to stop igniting its air-fuel mixture. A spark plug is designed to receive a current of electricity at a particular time in the engine’s cycle to ignite the air-fuel mixture and cause combustion, allowing the piston to transfer this energy to be used. The spark plug does this by creating a large voltage difference at its firing end, which causes a spark across what is called the gap. The air-fuel mixture fills this gap and allows a large spark to be created igniting the mixture. Ideally the equation for combustion of octane and oxygen should yield only carbon dioxide and water molecules along with energy. This reaction is represented by the complete combustion equation above. When the mixture becomes too rich (an excess of fuel to air in the AFR ratio causing a λ<1) the cylinder is not able to burn all of its fuel as is shown in the low air combustion equation. This means that carbon begins building up along the firing end of the spark plug. When the engine is running properly, as in the realistic equation for combustion, the small amount of carbon on the firing tip is burnt off. What occurs with excess carbon is delayed firing times and eventually the spark plug will no longer be able to burn off the excess carbon, ceasing to fire. This is what is known as carbon fouling and can be a great indicator as to what is happening inside the engine. To correct this problem the spark plug must be cleaned of its excess carbon. A possible way to do this is to run the engine at higher speeds which would cause greater temperatures in the cylinder allowing the spark plug to become clean. The problem with this is it assumes the spark plug still has the ability to fire within the cylinder. If no firing can occur, than a new spark plug must be acquired. Also, the ratio of air to fuel being sent into the cylinder must be adjusted to a more balanced one according to the engine’s specifications, which can be found in its manual from the manufacturer.

• Denotes information based upon information found on www.Wikipedia.com

1 Denotes information based upon information found on www.ngksparkplugs.com

Product Reassembly Plan

Below is a step by step process on how to reassemble the pressure washer engine that was taken apart in the sections above. By maintaining the organization as suggested in the disassembly section, all major parts below should have the proper bolts, nuts, and other small parts associated with its reassembly already together. By doing this a bolt from the throttle would not be used as a fastener for the engine block and only the size tool needed is listed, not the qualities of the bolt, nut, etc.

1) Piston Assembly

a) Connect the piston to the connecting rod by inserting the piston pin

b) The connecting is rod connected to the crank shaft by 2 10mm bolts and its bottom half

i) Point: make sure the fin on the bottom part of the connecting rod faces downward

2) Cylinder head with valve assembly

a) Place valves back into cylinder head

b) Place springs on top of valves

c) Put spring retainer on spring

d) Caps on top of valves

e) Rocker arm-round side down on imbedded bolts

f) Spacer nut on bolt pushed into rocker arm nut end up

g) Small hex nut placed last to hold spacer nut in place

h) Place pushrods in the two slots at the bottom of the machined surface of the engine block so that :they can be actuated later by the cams

i) Align head gasket so that it will not cover any holes when placed between cylinder head and engine block

j) Slide cylinder head with valves over pushrods to be secured to the engine block

k) 4 12mm bolts secure the head to the engine block.

l) Taking the cylinder cover place on top of the cylinder head and secure with its 4 5/16” bolts.

2) Engine block

a) Slide camshaft such that its main cam gear aligns with the internal gear of the crankshaft.

b) Bolt case cover to engine block using 6 10mm bolts

3) Flywheel-ignition

a) The flywheel was not removed so it should be easy to locate.

b) While holding the plastic cooling fins place the roll pin cage such that the central hole is not :covered.

c) Slide these parts onto the bolt that sticks out of the flywheel

d) Using a 21mm wrench attaches the accompanying nut to the flywheel bolt over the roll pin cage :and cooling fins.

e) Facing the flywheel such that the cylinder head is on the left, replace the spark plug by hand in :the cylinder head.

f) Attach the ignition wiring on the outside of the engine block to the left of the flywheel and right of :two visible extruding bolts. This is done with 2 bolts using 5/16 wrench

g) The other end of the ignition wiring gets capped onto the spark plug

h) There is a metal plate that is bolted under the cylinder head with 3 5/16 bolts. Secure the plate to :a hole below the exhaust outlet and one right below the cylinder head cap. The last one is used :with the pull start assembly.

i) Attach pull start assembly using 4 5/16” bolts such that it aligns over the roll pin cage. One goes :through the metal plate in the previous step.

4) Carburetor and Choke base

a) Slide carburetor onto two extruding bolts to the right of the flywheel.

b) Slide choke base on next

c) Secure with two acorn nuts by hand

5) Throttle Assembly

a) Point this requires looking at the adjacent picture for clarification

b) There are two larger metal pieces. The one on the left in the image is to be attached first.

c) The cotter pin is pushed into a groove on a small black rod that comes out of the engine block :top.

d) Above this pin rests the more slender portion of the throttle.

e) A t-bolt is slid horizontally through that part of the throttle and is held in place by a flange hex nut.

f) The larger portion is bolted to the block and to the cylinder head (next to the spark plug) with 2 5/16’’ bolts.

g) A metal rod attaches from the piece on the right to a small black piece on the carburetor

h) The smaller spring attaches in the same manner and can be seen more clearly in the pictures.

6) Gas tank

a) The carburetor has a tube which can be thread into the bottom of the gas tank

b) After threading the tube in, the engine can be placed on top of the engine as seen in the picture.

c) The tank has two bolt threads already on it that are secured to the tank with 2 10mm nuts. A bolt :(8mm) on the opposite side next to the throttle completes this step.

7) Exhaust

a) With the exhaust is a gasket that slides over the two bolt threads extruding from the exhaust.

b) The actual exhaust assembly is slid over these bolt threads and secured with two hex nuts (1/2”)

8) Air Intake

a) Secure base of air intake above carburetor using the button and flat head screws

b) Next place air filter over base. Secure with wing nut.

c) Place cover over the filter and secure with another wing nut.

9) Engine to frame

a) Align engine such that the four holes on the base line of with the holes on the frame.

b) Secure by putting 4 1/2” bolts through the engine into the frame with 4 10mm bolts securing the :bolts in place

10) Fuel pump

a) Attach the fuel pump to the base of the pressure washer 2 8mm bolts

b) Attach single end hose line to open port in gas tank

c) Attach double end hose line to hole in carburetor and the other hole it lines up with.

d) Finish connecting loose wires by the on/off switch, matching colored wire together.

Challenges:

The piston must be oriented correctly to be reassembled within the cylinder. The problem with the piston is that it has four ways that it can be put into the cylinder, only one of which is the correct way. The correct way is to place the piston and connecting rod base in the cylinder, such that the base’s fin and overall piston is angled downward, toward the bottom of the engine block. The group assessed the positioning of the crankshaft and gears within the block and decided this was the only possible method that would insure proper function of the engine.

The throttle provided much difficulty when reassembling. This was because of the various small components such as the springs and connecting rods that held it together had several possible arrangements. The group closely analyzed the design of the throttle and with the aid from a picture from disassembly, was able to properly reassemble the throttle.