Group 35 - Leaf Blower Engine

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Contents

Wholeengine.jpg


Executive Summary

The leaf blower engine discussed below underwent a multitude of dissection, analysis, and reconstruction. A seamless flow of inter-working component precision allows for this seemingly simple devise to function in a useful way. Our dissection of the product enforced our basic understanding of the engine. Through diligent dissection, the engine was completely stripped down to its individual key components. Each part was thoroughly examined and studied thereby completing our mental picture of the system as a whole. With an excellent understanding of the engine and its real world functionality, several constructive suggestions were informally proposed as design revisions. In accordance with our technical knowledge of the engine and the leaf blower system researched on its Homelite consumer website (see Reference), it is believed that our ideas for improvement could make for a more ideal product.

Request for Proposal

Request For Proposal

Preliminary Design Review

Causes for Corrective Action
Essentially our work proposal and management proposals have gone according to the plan. All of our group members have contributed evenly, including meeting regularly and working in a timely fashion. The work is divided evenly according to each group members’ strengths. As far as our disassembly process as described in our work proposal, we were mostly accurate. Some of the tools outlined were not required. “The tools required for this are flathead and Phillips head screw drivers of various sizes, metric sockets and wrench set, needle nose pliers, hex (torx) keys, and allen keys, all of various sizes.” What we used were the metric sockets and wrench set, need nose pliers and torx wrenches, and Phillips head screw driver. We didn’t use the allen keys, or the flat head screwdriver. The time we proposed it would require was a slightly over estimated. “The whole process of disassembly should not take longer than one to two hours, as it is a small engine.” The process was only around 45 minutes, for disassembly and reassembly.

Product Dissection Plan

Product: Homelite Serial #HP3400590 (Utility #08026C) 2-Stroke

System Parts Disassembly Description (Est. Time) Difficulty Tools Used
Exhaust System - Muffler Cover/Body,- Internal Packing,- Exhaust Gasket The exhaust is held on with two t25 torx bolts. The exhaust system itself was missing the internal packing used for sound muffling. (3 min) 1 T25 torx
Gas Tank Tank and the Cap Held on by crank case cover (4 short T25 torx bolts) 1 T25 torx
Air Filter Assembly Cover/Body,Air Filter,Gasket The air filter is directly mounted to the carburetor with two 10mm bolts. No air filter material found inside the casing. (5 min) 1 10mm wrench
Carburetor System Float Bowl,Primer,Main Body,Spacer The float bowl of the carburetor is held on with two Phillips head screws, as is the primer bulb. The spacer between the carburetor and the cylinder, and the carburetor itself is held on with two T25 torx bolts. (15 min) 1 Phillips head screw driver
Flywheel Cover Body Cover,Rope,Spring There was no pull start assembly/flywheel cover present. If it were present, it would be held on with 4 T25 torx bolts that were provided. (5 min) 1 T25 torx
Ignition System Spark Plug,Spark Plug Wire,Solenoid One T25 torx bolt held the magnetic solenoid to the crank. (3 min) 1 T25 torx
Flywheel Assembly Flywheel,Bushing,Key The flywheel is held by a large aluminum nut that is easy to unscrew, however a torque wrench is required to tight it back up. The bushing slides of the flywheel with ease.

(5 min)

1,1,1,5
Cylinder The top cylinder block is only held by 3 long screws which must be torque wrenched during assembly process.(5 min) 1 T25 torx
Base Gasket 1
Crank Shaft 1
Piston Assembly Piston,Piston Ring,Connecting Rod,Wrist Pin To remove the connecting rod from the piston, snap ring pliers are needed, which are not provided in the dissection lab. Also, the piston ring was absent. (10 min) 1,5,3,5,5
Block Assembly Main Block,Open Bearing,Sealed Bearing We left the crank in the crank case; we needed a small press to remove the bearings to retrieve the crank assembly, without rendering the bearings useless. 1,1,5,5

Note: Bold reference couldn’t be separated. Italics represent missing parts such as exhaust packing, exhaust gasket, flywheel cover, pull start cover/body/rope/spring, piston ring.
Tool Used Reference:
  1. 10 mm socket
  2. 10 mm wrench
  3. T25 torx wrench
  4. Phillips-head screw driver

Difficulty Reference:
  1. Easy
  2. Medium
  3. Hard
  4. Complex
  5. Impossible without specially designated tools

Coordination Review

Component Summary

Part Name Quantity Material Function Manufacturing Process Model/Part Number Applied Force Complexity Functional or Cosmetic Image
Exhaust 1 Aluminum exit point for the burnt gases from the engine and also lower the sound output Metal Stamping not provided N/A 2 Functional
Exhaust.JPG
Gas tank with cap 1 Plastic Holds gasoline and delivers it to the carburetor Injection Molding not provided N/A 2 Functional
Tank.JPG
Air filter 1 Plastic Provide clean air to the carburetor Die Casting not provided N/A 1 Functional
Filter.JPG
Carburetor 1 Aluminum Supply fuel and air mixture to the engine Investment Casting not provided N/A 5 Functional
Carb.JPG
Fly wheel 1 Aluminum Produce electricity for the engine Die Casting not provided Centripetal 3 Functional
Fly wheel.JPG
Ignition system 1 Combination of Metal and Plastic Convert the electricity generated from the fly wheel to a spark for the spark plug. assembled by hand not provided N/A 5 Functional
Ignition.JPG
Cylinder 1 Aluminum The cylinder is a where the combustion takes place of the air and gas mixture, from the pressure provided by the piston and the spark provided by the ignition system. Die Casting 06825 Compressive 3 Functional
Cylinder.JPG
Gaskets 1 Paper Provide sealing for different components. There are gaskets between the cylinder and block, the carburetor and the cylinder, and exhaust stamped not provided n/a 1 Functional
Gaskets.JPG
Piston 1 Aluminum Reciprocate up and down inside the cylinder providing pressure for the combustion process Die Casting not provided Compressive 3 Functional
Piston.JPG
Connecting rod 1 Aluminum Connects the piston to the crank and provides the up and down motion Die Casting not provided Tensile 3 Functional
Connecting rod.JPG
Block 1 Aluminum Houses the main engine components. All of the other components either bolt to or go inside the block Die Casting not provided Compressive 4 Functional
Block.JPG
Bearings 2 Steel Provide less resistance in the spinning shafts of the crank not provided Centripetal 3 Functional
Bearing123.JPG
Bolts 25 Steel Attach different components of the engine to one another Die Casting not provided Shear and Compressive 2 Functional
Hardware.JPG




Design Revisions

1. A slight increase in engine displacement would be increase power, resulting in a more powerful leaf blower. With more blowing power, the user will be more satisfied in the product because of it's increased efficiency. This would be done in the beginning of the design process, and would not be overly expensive addition. The slight increase in cost would be made up for an increase in sales due to a more capable leaf blower.

  • Advantages: Increased power

Increased efficiency Higher sales

  • Disadvantages: Higher initial cost



2. A higher quality exhaust would not only be a good improvement for the user, but any one in the vicinity of the leaf blower. The current exhaust system is a simple aluminum shell, that is supposed to have a packing material inside, however ours is missing. To replace this with a tubed exhaust with a silencer would greatly decrease the sound output of the motor. The addition of a higher quality exhaust could be fairly expensive in comparison to the current design, due to the current design being so primitive, but having a more muffled engine is in the interest of users and neighbors alike.

  • Advantages: Decrease sound output

More satisfied customer Higher sales

  • Disadvantages: Higher initial cost

Increased complexity (capacity to result in decreased reliability)

3. There is a plastic spacer between the carburetor and the cylinder. It could easily be eliminated by making a slight design revision in the carburetor. Doing this would decrease production costs because the part would no longer be necessary. Having a less complex product, is in the interest of the manufacturer because it eases in the manufacturing and design process, and also cuts down on cost.

  • Advantages: Fewer parts

Less Complexity Higher sales

  • Disadvantages: Design revisions on carburetor has potential to be costly



Engineering Analysis

Problem Statement

In a leaf blower engine the piston should support a maximum temperature, compression and a maximum pressure. If the piston ring is broken in some way the gas volume will change and a significant compression loss will be there. Determining that compression loss.


Diagram:

Basic2strokengine.jpg
The combustion chamber is where our initial volume and clearance volume is calculated. Our engine is a Homelite two stroke with a displacement of 26 cc which can be converted to .026 liters. Clearance volume is when the piston is at the top of the stroke.

Assumptions

  • The initial volume to be V_i=400CMF. (cubic feet per minute) http://www.cpohomelite.com/products/zr08550.html
  • The leaf blower engine is 26cc.
  • If there is a compression lose, the clearance volume would be higher than the usual.
  • Calculations are based only according to the above diagram, which is considering only the piston system.
  • Compression ration 10:1 = V_i: V_C


Governing Equations:

C_r=((V_i+V_C ))/V_C


C_r=(((π/4×d×l)+V_C ))/V_C


  • C_r= compression ratio
  • V_i= initial volume
  • V_C= clearance volume
  • d= diameter of the cylinder
  • l= length of the piston



Calculations


10=((400CMF+V_C ))/V_C

V_C=44.44 CMF



V_i V_c C_r
400 45 9.89
400 50 9.00
400 60 7.67
400 70 6.71
400 80 6.00
400 90 5.44
400 100 5.00

Solution Check
All the values are calculated in CMF(cubic feet per minute¬), and the compression ratio has no units considering a ratio has no units. Then values which I got for my answers are reasonable according to the equation I used, because all of these numbers are within reasonable limits, so it seems our calculations are accurate.

Discussion of Results
  • Then calculated values show that, when the clearance volume is increased it directly affect the decreasing of the compression.
  • As to the above calculation we can see that if the piston ring is damage somehow, it will affect the efficiency of whole system.
  • As I increase the clearance volume calculations shows that it drop down to 10:5= V_i: V_C .
  • This is a two stroke engine and those won’t last longer as other engine types, because of that regular maintain is a must if needed to keep it running.
  • If maintaining process is ignored then users will encounter situations as above mentioned.
  • Regular maintaining will keep the engine perfect condition and it will deliver better performance.

Failure Modes and Effects Analysis (FMEA)
  • Probability – The loss of compression is one of the highest causes of horsepower loss in any internal combustion engine. The probability of failing is strongly dependant on the age of that particular combustion engine and how hard it was used.
  • Severity – The compression loss strongly affects the performance of the engine; if the compression is low enough, the engine wouldn’t start therefore failures are common. However if the compression fails, the engine would still be able to perform, but not at its peak.
  • Prevention – To check for the compression in each cylinder, use Cylinder Compression Tester and compare the values to the initial manufacturer specifications. If the compression is low, then the problem could be fixed by replacing piston rings and or boring the cylinder banks to eliminate scratches and replacing with the correct size rings after boring.

Critical Design Review

Product Reassembly Plan

Initially the leaf blower engine was not operational due to the lack of missing star up assembly and the piston ring as well as other systems were not inspected to be operational such as spark plug from the ignition system due to the missing components. After the reassembly was complete, the engine was not able to perform, however it's in the operational status. No major differences were recorded except for the use of the torque wrench that was used to tighten the bolts around certain areas such as engine block and cylinder block to specifications. Moreover, no other tools or difficulties were found during the reassembly.

Product: Homelite Serial #HP3400590 (Utility #08026C) 2-Stroke

System Parts Reassembly Description (Est. Time) Difficulty Tools Used Image
Block Assembly Main Block,Open Bearing,Sealed Bearing Begin with main block and insert the base gasket onto the top being sure to align the holes. 1,5,5 no assembly required
Block35.JPG
Crank Shaft No reassembly required. The crank shaft is already installed inside the main block. 1 already assembled
Crank35.JPG
Piston Assembly Piston,Piston Ring,Connecting Rod,Wrist Pin Place the connecting rod with the piston attached onto the crank shaft. Do this by aligning the hole on the lower end of the connecting rod onto the round crank shaft. 1,5,3,5 already assembled
Piston35.JPG
Cylinder Place the cylinder over the piston and bolt to the main block and base gasket using the 3 long bolts which must be torque wrenched during assembly process.(5 min) 1 T25 Torx
Cylinder35.JPG
Carburetor System Float Bowl,Primer,Main Body,Spacer The carburetor was not completely disassembled. The float bowl of the carburetor is held on with two Phillips head screws, as is the primer bulb. Include the black spacer between the cylinder and the carburetor which is held on with two T25 torx bolts. Also place the gasket between the carburetor itself and the cylinder. 1 T25 Torx, Phillips head screw driver
Carb35.JPG
Flywheel Assembly Flywheel,Bushing,Key Bolt the flywheel to the crank shaft using an aluminum bushel and the nut provided. The flywheel must be aligned with the key way on the crank shaft as shown in the image. 1,1,5 10mm wrench
Flywheel35.JPG
Ignition System Spark Plug,Spark Plug Wire,Solenoid Screw a single T25 torx bolt which holds the magnetic solenoid to the cylinder. Press the spark plug cap onto the spark plug. 1 T25 Torx
Ignition35.JPG
Flywheel Cover Body Cover,Rope,Spring There was no pull start assembly/flywheel cover present. If it were present, it would be held on with 4 T25 torx bolts that were provided. 1 T25 torx
Flywheel35.JPG
Air Filter Assembly Cover/Body,Air Filter,Gasket The air filter is directly mounted to the carburetor with two 10mm bolts. No air filter material found inside the casing. Include the gasket between the aif filter assembly and the carburetor. 1 10mm wrench
Filter35.JPG
Gas Tank Tank and the Cap Use 4 T25 torx bolts to hold the gas tank to the block. Also make sure that the small, black, rubber stoppers are intact to the gas tank to hold it more securely in place. 1 T25 Torx
Tank.JPG
Exhaust System - Muffler Cover/Body,- Internal Packing,- Exhaust Gasket The exhaust is bolted to the cylinder using two T25 Torx bolts. The exhaust system itself was missing the internal packing used for sound dampening. 1 T25 Torx
Exhaust.JPG

Note: Bold reference couldn’t be separated. Italics represent missing parts such as exhaust packing, exhaust gasket, flywheel cover, pull start cover/body/rope/spring, piston ring.
Difficulty Reference:
  1. Easy
  2. Medium
  3. Hard
  4. Complex
  5. Impossible without specially designated tools

Delivery


Slide 2.jpg Slide 3.jpg Slide 4.jpg Slide 5.jpg

References

http://www.cpohomelite.com/products/zr08550.html