Group 28 gate 3

This page is very long as it contains the full component list, design revision selections, CAD drawings of the piston assembly, and an engineering analysis section of possible engine failures.

Group 28 main page:

http://gicl.cs.drexel.edu/wiki/Group_28_-_Pressure_Washer

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	Aluminum	Creates the proper mixture of fuel and air for efficient combustion.	Formed	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.

Component Discussion

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.

Carburator The Carb is designed to premix the air and fuel before it is sent into the cylinder for ignition. It works on the principle of a vacuum sucking fuel from the fuel line by air moving past the opening. The amount of fuel and air being mixed, therefore controlling the power output of the engine, is controlled by opening and closing a valve actuated by the throttle. Another feature of this carburator is the choke valve. The choke valve is designed such that it can be closed to allow more fuel to be drawn into the carb for a richer air fuel mixture. This allows the engine to run from a cold start. The materials need not have high yeild strength because the pressure and forces acting on it are not that large. The valves and other metal are most likely aluminum because aluminum is easily shaped and is lightweight.

To see a short clip of our carburator click the link below:

http://www.youtube.com/user/dreilly3#p/a/u/0/4aRy4Jjuwjg

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

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.

Pin	Connecting Rod	Piston Head	Rod Base	Actual Assembly

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 found on www.Wikipedia.com

1 Denotes information found on www.ngksparkplugs.com