sign in sign up
<<
Home , Ball bearing, Compression ratio, Cylinder (engine), Cylinder head, Engine configuration

Design of a Variable Compression Internal Combustion A Major Qualifying Project Report Submitted to the faculty of Worcester Polytechnic Institute In partial fulfillment of the requirements for the Degree of Bachelor of Science In Mechanical Engineering

By: Liam Finnegan Quinton Schimmel

Submitted On: May 18, 2020

Project Advisor: Robert Daniello

2 Design of a Variable Compression Internal Combustion Engine Acknowledgements

We would like to primarily thank Professor Daniello for advising us on this project. He was always well-informed regarding the topics and provided helpful feedback in a timely manner. We would also like to thank Ian Anderson, a member of the Washburn Shops Laboratory Staff for his help with understanding the manufacturability and tolerances of the components we were designing.

3 Design of a Variable Compression Internal Combustion Engine Abstract

The purpose of this project is to design a single internal combustion engine to be used by the Mechanical Engineering Department at WPI to aid in class demonstrations. The engine must be reconfigurable for different operating parameters, and durable enough to withstand sub-optimal operating conditions. It must be able to function with a and that can be adjusted from 4:1 to 25:1 and able to operate using both and diesel . The design focuses on the components that are unique to this engine: Acme threading around the cylinder that allows the compression ratio to be varied while the engine is running, a unique , and a train that maintains consistent as the compression ratio is varied. The engine is designed with the intent to be manufactured by WPI’s shop. The result of this project is detailed drawings of the parts, enabling a future team to manufacture the engine.

4 Design of a Variable Compression Internal Combustion Engine Table of Contents Acknowledgements ...... 2 Abstract ...... 3 Table of Contents ...... 4 Table of Figures ...... 5 List of Tables ...... 5 Introduction ...... 6 Background ...... 8 Internal Combustion Engine Overview ...... 8 Ignition and Compression Ratio ...... 10 Engine Design ...... 12 Cooperative Research Engine ...... 15 Designs and Specifications ...... 18 Case ...... 21 Variable Compression Ratio and Cylinder Design ...... 23 Assembly and Crank Shaft ...... 27 Timing Assembly ...... 29 Valve Train and ...... 31 Conclusions and Recommendations ...... 33 Future Work ...... 34 Appendix A: Bill of Materials ...... 35 Appendix B: Drawings ...... 38 References ...... 56

5 Design of a Variable Compression Internal Combustion Engine Table of Figures Figure 1: Four- Cycle ...... 9 Figure 2: The Ideal ...... 10 Figure 3: Compression Ratio ...... 11 Figure 4: V-Configuration Engine ...... 13 Figure 5: Piston Diagram ...... 14 Figure 6: Overhead Valve Diagram ...... 15 Figure 7: Views of the Cooperative Fuel Research Engine ...... 16 Figure 8: Final Assembly ...... 19 Figure 9: Final Assembly Cross Section ...... 20 Figure 10: Crankcase Front View ...... 22 Figure 11: Crankcase Rear View ...... 23 Figure 12: Cylinder Height Lowest Configuration ...... 24 Figure 13: Cylinder Height Middle Configuration ...... 25 Figure 14: Cylinder Height Highest Configuration ...... 25 Figure 15: Vibration Reduction Springs ...... 26 Figure 16: Piston Assembly Front View ...... 28 Figure 17: Piston and Assembly...... 28 Figure 18: Timing Assembly ...... 30 Figure 19: Cylinder Head Top View ...... 31 Figure 20: Cylinder Head Bottom View ...... 32 Figure 21: Drawing of Entire Assembly ...... 38 Figure 22: Drawing of Crankcase ...... 39 Figure 23: Drawing of Cylinder Nut Brace ...... 40 Figure 24: Drawing of Timing Rod Brace ...... 41 Figure 25: Drawing of Cylinder ...... 42 Figure 26: Drawing of Crank Case Cover...... 43 Figure 27: Drawing of Timing Assembly Cover ...... 44 Figure 28: Drawing of Crankshaft ...... 45 Figure 29: Drawing of Crankshaft Counterweight and Wrist Pin...... 46 Figure 30: Drawing of Cylinder Nut ...... 47 Figure 31: Drawing of Cylinder Nut Shaft ...... 48 Figure 32: Drawing of Cylinder Head ...... 49 Figure 33: Drawing of Valve Cover ...... 50 Figure 34: Drawing of Connector Cover ...... 51 Figure 35: Drawing of Camshaft Connector...... 52 Figure 36: Drawing of Camshaft ...... 53 Figure 37: Drawing of Timing Rod ...... 54 Figure 38: Drawing of ...... 55

List of Tables Table 1: Cylinder Height Specifications ...... 27 Table 2: Bill of Materials ...... 35

6 Design of a Variable Compression Internal Combustion Engine Introduction

Physical objects and demonstrations as in-class teaching aids, when used effectively, improve student learning and curriculum retention (Crouch, Fagen, Callan, & Mazur, 2004). When students simply observe demonstrations, there is no noticeable improvement in learning; when students engage in class demonstrations by making predictions and discussing what they see, there is a significant improvement in information retention and understanding. A two year study in which lectures were supplemented with either practice problems, in-class demonstrations, or online discussions showed relevant classroom demonstrations to positively effect student learning (Staveley-O'Carroll, 2015).

Teachers can use class demonstrations to help students visualize and learn new topics.

The mechanical engineering department at Worcester Polytechnic Institute already utilizes physical visual aids and demonstrations in their curriculum. Everyday objects are used in “Kinematics of

Mechanisms” to simulate a linkage mechanism. Students can use the objects to understand the motion of the linkage, and how governing equations apply to and dictate the motion. Additionally, toys and arbitrary objects are used in “Introduction to Engineering Design” to help students understand key principals of engineering design. Students analyze the objects to understand effective design techniques or to see how poor design choices reduce product functionality. The mechanical engineering department could benefit from having a working reciprocating internal combustion engine to demonstrate engineering principals and the governing dynamics of internal combustion .

The purpose of this project is to design a singly cylinder internal combustion engine to be used by the Mechanical Engineering Department at Worcester Polytechnic Institute to aid in-class demonstrations. To do this effectively the engine needs to have a compression ratio that can be varied by the user while the engine is operating, a valve train that maintains consistent valve timing as the compression ratio is altered, and a crank case that provides the user with the ability to add additional 7 Design of a Variable Compression Internal Combustion Engine components and instrumentation. The engine must be easily maintained and reconfigurable for different operating parameters, as well as durable enough to withstand sub-optimal operating conditions causing extreme loads. The design needs to ensure relatively simple manufacturing and assembly.

8 Design of a Variable Compression Internal Combustion Engine Background

Internal Combustion Engine Overview

A four-stroke internal combustion engine involves a piston that completes four separate strokes as the crankshaft rotates (Proctor & Cromer, Gasoline Engine, 2019). One stroke is complete when the piston has moved the full length of the cylinder in either direction, thus each cylinder completes one full four-stroke cycle every two crankshaft rotations. These four strokes, , compression, expansion, and exhaust, create the four-step cycle that allows the engine to produce power; in a two-stroke cycle

(common in engines) intake and exhaust occur simultaneously, allowing the cycle to be completed in half the time of a four-stroke engine at the same rpm. During the intake stroke, the intake valve opens as the piston is moving downward (How a 4-Stroke Engine Works, n.d.). This allows for an air-fuel mixture to enter the cylinder . After the cylinder is filled with the mixture, compression begins. The intake valve is closed and the piston travels upwards and compresses the mixture against the cylinder head. The third step is considered the power stroke, but is also commonly referred to as the combustion stroke. In spark-ignition engines the ignites the air-fuel mixture; in diesel engines, the mixture ignites spontaneously as a result of the extreme temperatures and pressure caused by compression (Proctor & Cromer, Diesel Engine, 2019). The heat created by the spark plug causes the gases to rapidly expand, which then forces the piston in a downward motion until it reaches the bottom of the cylinder bore and provides mechanical power output through the crankshaft. This leads to the fourth step, the exhaust stroke. The exhaust valve is opened as the piston begins its upward motion again. As the piston ascends, the spent combustion gases are forced through the exhaust valve. When the piston reaches the top of the cylinder bore, the exhaust valve closes and the intake valve reopens, and the process will repeat. 9 Design of a Variable Compression Internal Combustion Engine

Figure 1: Diesel Engine Four-Stroke Cycle (Proctor & Cromer, Diesel Engine, 2019)

Figure 1: Diesel Engine Four-Stroke Cycle depicts the four-stroke cycle in a diesel engine. The principal difference between diesel and spark ignition is the manner in which the fuel is ignited (and hence the fuel itself); the manner in which the piston and operate is the same for all four stroke engines. In a gasoline engine a spark plug is placed at the top of the cylinder, and ignites the air-fuel mixture near top of the compression stroke. Gasoline engines operate using spark ignition of the air-fuel mixture. The flame front propagates outward from the ignition point at the spark plug (Proctor &

Cromer, Gasoline Engine, 2019). As the mixture is burning, the piston is being pushed downwards by the expanding gasses, causing the mixture to dissipate away from the spark plug. This can result in pockets of unburned air-fuel mixture that reduces the efficiency of the engine. Diesel engines operate using spontaneous ignition of the fuel instead of a spark plug. Spontaneous ignition of the air-fuel mixture is caused by the extreme pressures and temperatures inside the cylinder with the appropriate fuel type

(Proctor & Cromer, Diesel Engine, 2019). Combustion happens throughout the air-fuel mixture simultaneously, causing detonation instead of deflagration. Diesel engines have higher compression ratios which results in a higher efficiency. 10 Design of a Variable Compression Internal Combustion Engine Ignition and Compression Ratio

An engine’s compression ratio is the ratio of the volume of the air-fuel mixture in the cylinder when the piston is at its lowest point (bottom dead center) and the volume when the piston is at its highest (top dead center), depicted in Figure 3 below. The compression ratio provides important insight into an engine’s performance (Lee, 2018). How the compression ratio affects the performance of the engine can be understood through the thermodynamics of the Otto cycle as seen in Figure 2. The Otto cycle is the four-stroke cycle described in the section above.

Figure 2: The Ideal Otto Cycle (Nasa, 2015)

The line between represents 3 and 4 represents combustion and the highest pressure reached during the cycle, and the line between represents 5 and 6 represents the lowest compression achieved when the piston is at bottom dead center (Nasa, 2015). The thermodynamic efficiency of an engine is how well it converts the energy caused by combustion to mechanical work, and is a function of 11 Design of a Variable Compression Internal Combustion Engine temperature. It is represented in the figure above by the area under the curve. The greater the temperature difference between steps 4 and 6, the greater the thermodynamic efficiency. Since pressure and temperature are linearly dependent, as the pressure in the air-fuel mixture increases, so does the temperature. Thus, as the compression ratio of the engine increases, so does the thermodynamic efficiency and consequently the power output. Additionally, the air-fuel mixture being compressed into a tighter space facilitates flame propagation, resulting in more complete combustion and improved (Proctor & Cromer, Gasoline Engine, 2019).

Figure 3: Compression Ratio (Lee, 2018)

Engine knock in spark ignition engines is unwanted, spontaneous, premature ignition of the air- fuel mixture at one or more locations in the . This results in the cylinder pressure rising too rapidly which creates a knocking sound. This deflagration, and potentially detonation, of the air-fuel mixture occurs while the piston is still traveling upward during the compression stroke, applying force that opposes the rotation of the engine (Lee, 2018). This causes decreased performance and efficiency, and can result in mechanical failures and potentially dangerous operation. A primary cause of engine knock is a compression ratio that is too high. In the ideal Otto cycle, the is assumed 12 Design of a Variable Compression Internal Combustion Engine to be pure air which is an ideal gas. Compressing the air-fuel mixture adiabatically increases its temperature according to the ideal gas law. This assumption of adiabatic compression is reasonable since the compression is so rapid. Since fuels have a temperature threshold where spontaneous ignition occurs (auto-ignition temperature), different fuels have a limit to how much they can be compressed before spontaneous ignition occurs and the combustion results in engine knock. Gasoline has an auto- ignition temperature of approximately 536 degrees Fahrenheit, which limits the compression ratio to less than 15:1 (Ukropina, 2014). Since gasoline engines use a spark plug to initiate deflagration, lower compression ratios can still generate high power output (Taylor, 1985). Diesel engines operate with compression ignition rather than spark ignition, so the heating from compression must cause spontaneous ignition of the air-fuel mixture for the engine to function. Engine knock in diesel engines is difficult to mitigate, and can occur at low engine speeds and power outputs, as well as when the compression ratio is too high (above 25:1).

Engine Design

Despite differences in ignition methodology, engine cycle, or (boxer, inline, opposed piston, or v configuration), most reciprocating internal combustion engines have similar designs and major assemblies (Proctor & Cromer, Gasoline Engine, 2019). The piston assembly sits inside the cylinder and rotates with the crankshaft. The crankshaft is connected to the accessories and the valve train, which rotates the camshaft. The ignition assembly, if required, is either electronically or mechanically synced to the rotation of the engine to provide current through the spark plug at the correct time: slightly before the piston reached top dead center on the compression stroke.

The cylinder block is the main housing for the engine (Proctor & Cromer, Gasoline Engine, 2019).

The crankcase along the bottom contains the crankshaft, and cylinders are bored throughout the engine in their designated orientation. In-line engines orient the cylinder in a single row that runs the length of 13 Design of a Variable Compression Internal Combustion Engine the , whereas a v-configuration places the cylinders along two sides of the engine. The two rows are angled away from each other, with the crankcase and crankshaft in the middle as shown in

Figure 4.

Figure 4: V-Configuration Engine (Leinback, 2013)

The combustion chamber is the region of the cylinder located above the piston assembly. Valves in the top of the cylinder control air-fuel mixture intake and exhaust. In spark-ignited engines, the spark plug is located in the top of cylinder, typically in the center of the cylinder between the valves. The combustion process is explained further on page 8 and 9.

The are attached to the crankshaft through the wrist pin. Piston rings around the outside of the piston create a seal against the cylinder wall and prevent air-fuel mixture and exhaust gasses from escaping and entering the crankcase, as seen in Figure 5 below. Oil lubricates the piston rings against the cylinder wall and the connection of the piston rod on the crankshaft to reduce wear and counteract that could reduce the engine’s mechanical efficiency. 14 Design of a Variable Compression Internal Combustion Engine

Figure 5: Piston Diagram (University of Windsor, n.d.)

The rotating crankshaft is connected to the , which is used to transfer the engine’s rotation to the ’s transmission (Proctor & Cromer, Gasoline Engine, 2019). It is also connected the valve train, the , as well as a number of accessories that operate cooling fans and provide power to electrical components. There is a 2:1 gear reduction between the crankshaft and the camshaft since both sets of valves have to open in the time it takes for the piston and crankshaft to complete one full cycle (two rotations). Depending on the engine’s design, the camshaft could be located above the cylinders, or in the crankcase. Some engines use a single camshaft to open and close all the valves.

Pushrods run from the camshaft to each valve, and a rocker is used to transfer the motion from the 15 Design of a Variable Compression Internal Combustion Engine pushrod to the valve (diagram). In a dual overhead camshaft engine, each row of cylinders has its own camshaft located above the cylinders. This configuration eliminates the need for pushrods, but increases the size needed for the cylinder heads.

Figure 6: Overhead Valve Diagram (, n.d.)

Cooperative Fuel Research Engine

The cooperative fuel research engine was designed by the Waukesha Motor Company in 1928 and was built and tested in 1929 (The Waukesha CFR Fuel Research Engine, 1980). The purpose behind designing the engine was to develop an improved gasoline knock-test method. The creation of the CFR engine established a higher standard of defining fuel quality. It allowed the automotive and petroleum industries to produce better quality products and paved the way for a significant advancement in fuels and engines.

In order to accommodate some of the issues that occurred during fuel testing, the design of the

CFR engine contained some unique modifications that were not common in other previous engines (The

Waukesha CFR Fuel Research Engine, 1980). The premier modification was the variable-compression 16 Design of a Variable Compression Internal Combustion Engine cylinder. This was done by relocating the valve assembly and turning it into an overhead valve type. The use of a compensating mechanism allowed the compression ratio to change between 3:1 and 30:1 by moving the piston within the cylinder without altering any valve adjustments. The connection between the cylinder and spark lever would give an accurate spark position regardless of the compression ratio.

The design also included a cast iron crankcase, a counterweighted crankshaft carried in large sleeve-like bearings, and a cast iron piston with five compression rings. All these features were included to ensure that the engine was durable and had a long life. Another interesting modification to the design was the installment of the knock meter. Knock is affected by compression ratio, spark timing, mixture and engine speed, which causes the fuel to burn unevenly and can be harmful to the engine. An electric knock meter was placed at the top of the unit control panel as a way to ensure that no irregularities were occurring during combustion, which helped streamline the fuel testing process.

Figure 7: Views of the Cooperative Fuel Research Engine (The Waukesha CFR Fuel Research Engine, 1980) 17 Design of a Variable Compression Internal Combustion Engine

The Waukesha CFR engine was recognized by the American Society of Mechanical Engineers for its ability to provide a more efficient gasoline-knock test method. There have been some small refinements to the original design since 1929, but the main design features remain the same. Almost a century later, the CFR engine is still in production, and has been the longest continually produced model in the company's history.

18 Design of a Variable Compression Internal Combustion Engine Designs and Specifications

The engine’s use as a demonstration tool for a teaching aid means that it needs to have functionality that is not normally found in production engines. The design of this MQP focused on the features that are unique to this engine. Primarily, the user needs to be able to manually alter the engine’s compression ratio while the engine is operating. The crank case must be designed to support this functionality, and the valve train needs to be able to maintain consistent valve timing as the compression ratio is altered. Since the compression ratio will be varied under operation, the engine needs to be durable enough to maintain safe operating conditions for the user, withstanding forces generated under extremely low and high compression ratios as well as engine knock. The crank case also needs to be designed to allow instruments and additional features to be easily added and removed from the engine, enabling the user to simulate and analyze any operating conditions. Figure 8 below depicts the assembled model of the four-stroke demonstration engine, and Figure 9 shows a cross section of the assembly. 19 Design of a Variable Compression Internal Combustion Engine

Figure 8: Final Assembly 20 Design of a Variable Compression Internal Combustion Engine

Figure 9: Final Assembly Cross Section

The crank case and rigid components are depicted in dark grey, rotating shafts the piston assembly are red, while the gears are orange and springs are green. The Acme nut is a dark yellow. All bearings, retaining rings, and bolts are blue, dark red, and faded yellow, respectively. The design only focuses on components and assemblies that are unique to this engine, so the intake manifold, ignition system, and are not modeled. These parts, along with all the bearings, retaining rings, gears, and bolts will be purchased from a retailer when assembling the engine. A detailed bill of materials in the appendix describes which parts should be manufactured and which should be purchased. 21 Design of a Variable Compression Internal Combustion Engine

When the four-stroke engine is configured to operate using gasoline, the spark plug at the top of the cylinder ignites the air-fuel mixture. As described in pages 8 to 9, the pressure forces the piston down causing the crankshaft to rotate. The large diameter bevel gear at the end of the crankshaft transfers the motion to the timing assembly along the left side of the engine in Figure 9 with a 2:1 gear increase. The bevel gear at the top of the timing shaft transfers the rotational motion to the valve train, where the open and close the valves. The Acme nut around the outside of the cylinder can be used to raise and lower the cylinder with respect to the crankcase, which changes the compression ratio of the engine. The top bevel gear on the timing shaft slides up and down the shaft with the cylinder head, keeping the crankshaft connected to the valve train at all times, without affecting the rotation of the camshafts with respect to the crankshaft to ensure consistent valve timing is maintained. The sections below describe the sub-assemblies in more detail.

Crank Case

The crank case (Figure 10 and Figure 11) is designed to be able to support the entire upper assembly, and is robust enough to withstand extreme operating conditions. Hole patters on the sides and bottom provide a means of attaching additional components and instrumentation to the engine, and allow the engine to be mounted rigidly to a table or testing apparatus. 22 Design of a Variable Compression Internal Combustion Engine

Figure 10: Crankcase Front View

The two-part brace on top of the crankcase holds the Acme nut in place while allowing rotational motion. An oil fill hole is located next to the braces, and holes for oil drain as well as an oil temperature and oil level sight gauges are drilled from the side into the bottom on the crankcase. Hole patterns on the front and back of the crankcase provide places to attach covers, as well as a brace to support the timing assembly (Figure 11). 23 Design of a Variable Compression Internal Combustion Engine

Figure 11: Crankcase Rear View

Bearings (blue) reduce wear on the crankcase while also holding the crankshaft in place, and retaining rings prevent any unwanted lateral motion.

Variable Compression Ratio and Cylinder Design

The demonstration engine designed in this MQP uses a similar method to the CFR engine to change the compression ratio: changing the cylinder height with respect to the piston assembly. The cylinder sits inside a large nut that the user is able to rotate. Large diameter external Acme threading

(not depicted) around the outside of the cylinder and corresponding internal threads on the inside of 24 Design of a Variable Compression Internal Combustion Engine the nut moves the cylinder with respect to the nut when it is rotated. The external thread is on the 3.5 inch outer wall of the cylinder. It has 2 threads per inch, and a maximum pitch diameter of 3.235

(Engineers Edge, n.d.). Fixing the nut to the crank case (but still allowing for rotation) lets the cylinder’s height change with respect to the crank case and piston assembly. The user can then change the compression ratio of the engine by rotating the nut. A removable handle enables the user to easily rotate the nut without the manufacturer having to attach a gear assembly to the top or side of the crank case.

Figure 12: Cylinder Height Lowest Configuration 25 Design of a Variable Compression Internal Combustion Engine

Figure 13: Cylinder Height Middle Configuration

Figure 14: Cylinder Height Highest Configuration 26 Design of a Variable Compression Internal Combustion Engine

Figure 12 above shows the cylinder in the lowest position, Figure 13 shows the cylinder in the middle, and Figure 14 shows the cylinder in its highest configuration.

A large diameter disc spring below the Acme nut provides enough upwards pressure to hold the nut against the brace and reduce vibrations caused by the friction between the piston rings and the internal cylinder walls; A secondary spring around the outside of the cylinder contacting the top of the nut keeps the Acme threads in constant contact so that the cylinder does not slip (both springs in green in Figure 15 below). The compression ratio of the engine is approximately 25:1 when the cylinder is at its lowest point and 4:1 when the cylinder is at its highest.

Figure 15: Vibration Reduction Springs 27 Design of a Variable Compression Internal Combustion Engine

Table 1 below summarizes the specifications of the cylinder assembly.

Table 1: Cylinder Height Specifications

Cylinder Position Bottom position Middle position Top position

Cylinder Height 0 0.4375 0.875 inches

Piston Clearance at Top 0.125 inches 0.5625 inches 1 inch

Dead Center

Piston Clearance at 3.125 inches 3.5625 inches 4 inches

Bottom Dead Center

Compression Ratio 25:1 6.33:1 4:1

Piston Assembly and Crank Shaft

The piston assembly is similar to that of a conventional reciprocating internal combustion engine, and should be purchased from a retailer as outlined in Appendix A: Bill of Materials since this assembly should be purchased, the CAD models are visual representations and not meant to be directly machined. The crankshaft transfers its rotational motion into linear motion through the piston rod and piston. Since the cylinder translates when the user alters the compression ratio, the piston assembly is in a fixed location within the crank case (Figure 16 and Figure 17 below). 28 Design of a Variable Compression Internal Combustion Engine

Figure 16: Piston Assembly Front View

Figure 17: Piston and Crankshaft Assembly 29 Design of a Variable Compression Internal Combustion Engine

Retaining rings around the outside of the crankshaft prevent linear motion, and a keyway cut into the end of the shaft allow a no-slip connection to a bevel gear in the timing assembly. The crankshaft has a 1-inch diameter to be able to withstand extreme forces and features a 3 inch stroke.

Timing Assembly

In a typical reciprocating internal combustion engine, the valve train is rigidly attached to the crankshaft through a timing chain. Since the valve train sits in the cylinder head (located on top of the cylinder), the height of the valve train will change whenever the user raises or lowers the cylinder; a timing chain cannot be used to connect the crank shaft to the valve train. A timing assembly that uses keyed shafts and a series of gears allows the valve train to stay connected to the piston assembly at all cylinder heights, as depicted in Figure 18 below. This is necessary since changing the compression ratio independently from the valve timing with alter the performance of the engine – refer to pages 9 to 12. 30 Design of a Variable Compression Internal Combustion Engine

Figure 18: Timing Assembly

Keyways along the primary shaft create no-slip connections with the bevel gears, and ball bearings and retention rings hold the assembly in place against the lateral force created by bevel gears.

The gears are modeled from McMaster-Carr. The 4 inch bevel gear is connected at 90 degrees to a 2 inch bevel gear that rotates the primary shaft, providing the 2 to 1 gear ratio needed for correct timing.

The 1 inch bevel gear that connects to the valve train is allowed to slide up and down with the cylinder head so that the connection between the crankshaft and the camshafts are preserved when the user changes the compression ratio. 31 Design of a Variable Compression Internal Combustion Engine Valve Train and Cylinder Head

The valve train is similar to that of a conventional single cylinder engine. An overhead camshaft design eliminates the need to use pushrods, and allows for easy access to the valve train for maintenance and adjustments, shown in Figure 19 and Figure 20 below. The spark plug located at the top of the cylinder and in the center of the chamber. Easy access through the cylinder head allows for easy maintenance, and provides the user with the ability to change or remove the spark plug to configure the engine to operate using gasoline or diesel fuels, or any other liquid combustible.

Figure 19: Cylinder Head Top View

32 Design of a Variable Compression Internal Combustion Engine

Figure 20: Cylinder Head Bottom View

The timing assembly is connected to the valve train through the ball on the left side of

Figure 19. The bevel gear on the timing assembly is secured inside the bearing, which slides the gear up and down the timing shaft when the compression ratio is changed. A matching bevel gear connects to the timing gear at a 90 degree angle. Since the piston assembly is centered in the cylinder, the crankshaft and thus the unique timing assembly needed for the variable compression mechanism are also centered in the engine. Utilizing a dual-overhead camshaft setup (refer to pages 12 to 15), each camshaft is equally offset from the center of the engine, so an additional shaft is required to translate the motion to the camshafts. 1 inch gears on the additional shaft and one of the camshafts resolves this problem without changing the gear ratio between the crankshaft and the valve train. 1.25 inch gears connect the camshaft at a 180 degree offset so that the valves are opened and closed in a four-stroke cycle.

33 Design of a Variable Compression Internal Combustion Engine Conclusions and Recommendations

Through this Major Qualifying Project, we were able to design a fully functional reciprocating internal combustion engine to be manufactured and used by the mechanical engineering department at

Worcester Polytechnic Institute for in-class demonstrations. The engine features the ability for the user to easily reconfigure the engine for different operating parameters. The crank case, variable compression cylinder mechanism, piston assembly, crankshaft assembly, timing assembly, and cylinder head and valve train are all designed uniquely to provide durability, effective operation, and simple adjustments. The covers can be made from any material, such as a clear acrylic or plexiglass so that the inner operations of the engine can be observed.

The engine is designed to be mostly manufactured with the use of WPI’s machine shop; a few parts have to be purchased separately. The bearings, retaining rings, valves and valve springs, spark plug and ignition assembly, , bolts, and instrumentation such as an oil temperature gauge will have to be ordered from retailers. The appendices, beginning on page 35, feature schematics of every part to be machined as well as a list of the parts that need to be ordered. The 3D models were designed with tolerances per the Machinists Handbook (Pohanish, McCauley, & Hussain, 2016), however, special care should be taken to dimensions and tolerancing when machining close-fit parts to ensure correct fitment and operation.

34 Design of a Variable Compression Internal Combustion Engine Future Work

This project was undertaken with the intention of designing, manufacturing, assembling, and testing the demonstration engine. Because of the circumstances, the project was never able to be manufactured or assembled. A future team is needed to use this report to assemble the engine to be used by the mechanical engineering department at WPI. The information provided throughout, as well as the bill of materials and the drawings in the appendices are intended to be used for the purpose of manufacturing the engine. Refer to Appendix A: Bill of Materials for information regarding purchased and manufactured parts. Some of the gears to be purchased from McMaster do not have keyways machined into them. This will have to be done to ensure that the gears spin on their shafts without slipping. Keyways have been designed into every shaft, and their measurements are shown in Appendix

B: Drawings – use these measurements as reference when machining keyways into the gears.

Appendix A: Bill of Materials

Note that parts to be purchased and not manufactured are marked as such in the bill of materials below. Many of these items have been included in the model exactly as their purchased counterparts would fit into the assembly, and CAD models of them can be assumed to be accurate. This pertains to all gears, ball bearings, the disc spring, and internal and external retaining rings.

Links to these parts have been placed in the bill of materials and should be used to purchase the items to ensure the components fit together. Some of the purchased items are up to the discretion of the future team assembling the engine to select and purchase. The CAD models of these parts are visual representations only, and not intended to be completely accurate. Additional design needs to be completed to alter the engine to fit the purchased parts once selected: valves (and cylinder head to match), valve springs, cylinder spring, bolts, and the piston assembly (and combustion chamber shape).

Table 2: Bill of Materials

Quantity Type Assembly Name Manufactured Purchased Material Relevant Link 1 Part Main Assembly Crankcase X Aluminum Figure 22: Drawing of Crankcase on page 39 2 Part Main Assembly Crankcase Cylinder Nut Brace X Brass Figure 23: Drawing of Cylinder Nut Brace on page 40 1 Part Main Assembly Crankcase Timing Rod Brace X Aluminum Figure 24: Drawing of Timing Rod Brace on page 41 2 Part Main Assembly Internal Retaining Ring – 2 inch Shaft ID X Steel 2 inch Internal Retaining Ring - McMaster 2 Main Assembly Part Ball Bearing – 1 inch Shaft OD X Steel 1 inch Ball Bearing - McMaster

1 Part Main Assembly Disc Spring – 3.5 inch ID X Steel 3.5 inch Disc Spring - McMaster 1 Sub-Assembly Main Assembly Cylinder Nut Sub-assembly 1 Sub-Assembly Main Assembly Crankshaft Sub-assembly 1 Part Main Assembly Cylinder X Cast Iron Figure 25: Drawing of Cylinder on page 42 1 Sub-Assembly Main Assembly Piston Sub-assembly 1 Sub-Assembly Main Assembly Cylinder Head Sub-assembly 19 Part Main Assembly Hex Bolt – ¼-20X0 Thread, ¾ inch X 1 Part Main Assembly Crankcase Cover X Any Figure 26: Drawing of Crank Case Cover on page 43 Main Assembly Hex Socket Screw – 3/8-16X0 Thread, 1 Part X 3/4 inch 1 Part Main Assembly Hex Bolt – ¼-20X1 Thread, 1 inch X Main Assembly Hex Socket Screw – ¼-20X0 Thread, 0.5 4 Part X inch 1 Part Main Assembly Timing Cover X Any Figure 27: Drawing of Timing Assembly Cover on page 44 Main Assembly Hex Socket Screw – NO5-40X0 Thread, 1 Part X 3/16 inch 36 Design of a Variable Compression Internal Combustion Engine

1 Part Main Assembly Ball Bearing – ¾ inch Shaft OD X Steel 0.75 inch Ball Bearing - McMaster 1 Sub-Assembly Main Assembly Timing Rod Sub-assembly 1 Part Main Assembly Bevel Gear – 1 inch Shaft OD X Steel 1 inch Ball Bearing - McMaster 1 Part Main Assembly Cylinder Spring X 1 Part Cylinder Nut Cylinder Nut X Brass Figure 30: Drawing of Cylinder Nut on page 47 1 Part Cylinder Nut Cylinder Nut Shaft X Any Figure 31: Drawing of Cylinder Nut Shaft on page 48 1 Part Crankshaft Crankshaft X Steel Figure 28: Drawing of Crankshaft on page 45 Figure 29: Drawing of Crankshaft Counterweight and Wrist 1 Part Crankshaft Crankshaft Counterweight X Steel Pin on page 46 External Retaining Ring – 1 inch Shaft 2 Part Crankshaft X Steel 1 inch External Retaining Ring - McMaster OD 1 Part Crankshaft Bevel Gear – 2 inch Shaft OD X Steel 2 inch Bevel Gear - McMaster 1 Part Piston Piston Head X Summit Racing 1 Part Piston Piston Pin X Summit Racing 1 Part Piston Piston Rod X Summit Racing 1 Part Piston Ball Bearing – ¾ inch Shaft OD X Steel 0.75 inch Ball Bearing - McMaster 3 Part Piston Piston Rings X Summit Racing 1 Part Cylinder Head Cylinder Head X Aluminum Figure 32: Drawing of Cylinder Head on page 49 4 Part Cylinder Head Valve X Summit Racing 1 Part Cylinder Head Ball Bearing – ¾ inch Shaft OD X Steel 0.75 inch Ball Bearing - McMaster 1 Part Cylinder Head Valve Cover X Aluminum Figure 33: Drawing of Valve Cover on page 50 Part Cylinder Head Hex Socket Screw – NO5-40X0 Thread, ½ 3 X inch Part Cylinder Head Hex Socket Screw – NO4-40X0 Thread, ½ 5 X inch 1 Part Cylinder Head Connector Cover X Any Figure 34: Drawing of Camshaft Connector Cover on page 51 1 Part Cylinder Head Spark Plug X N/A Spark Plug - NGK 4 Part Cylinder Head Valve Spring X Summit Racing 1 Part Cylinder Head Ball Bearing – ¼ inch Shaft OD X Steel 0.25 inch Ball Bearing – McMaster Part Cylinder Head Internal Retaining Ring – 7/8 inch Shaft 2 X Steel 0.875 inch Internal Retaining Ring - McMaster ID 1 Part Cylinder Head Ball Bearing – 3/8 inch Shaft OD X Steel 0.375 inch Ball Bearing - McMaster 1 Sub-Assembly Cylinder Head Cam Connector Sub-assembly Aluminum 4 Part Cylinder Head Ball Bearing – 1/2 inch Shaft OD X Steel 0.5 inch Ball Bearing - McMaster 2 Sub-Assembly Cylinder Head Camshaft Sub-assembly Aluminum 1 Part Cylinder Head Gear – 1 inch X Steel 1 inch Gear - McMaster Cam 1 Part Cam Connector X Aluminum Figure 35: Drawing of Camshaft Connector on page 52 Connector Cam External Retaining Ring – 3/8 inch Shaft 3 Part X Steel 0.375 inch External Retaining Ring - McMaster Connector OD Cam 1 Part Bevel Gear – 1 inch X Steel 1 inch Bevel Gear - McMaster Connector 37 Design of a Variable Compression Internal Combustion Engine

Cam 1 Part Gear – 1 inch X Steel 1 inch Gear - McMaster Connector 1 Part Camshaft Camshaft X Aluminum Figure 36: Drawing of Camshaft on page 53 1 Part Camshaft Gear – 1.25 inch X 1.25 inch Gear - McMaster 1 Part Timing Rod Timing Rod X Aluminum Figure 37: Drawing of Timing Rod on page 54 External Retaining Ring – ¾ inch Shaft 2 Part Timing Rod X Steel 0.75 inch External Retaining Ring - McMaster OD 1 Part Timing Rod Bevel Gear – 4 inch X Steel 4 inch Bevel Gear - McMaster

38 Design of a Variable Compression Internal Combustion Engine Appendix B: Drawings

Figure 21: Drawing of Entire Assembly 39 Design of a Variable Compression Internal Combustion Engine

Figure 22: Drawing of Crankcase 40 Design of a Variable Compression Internal Combustion Engine

Figure 23: Drawing of Cylinder Nut Brace 41 Design of a Variable Compression Internal Combustion Engine

Figure 24: Drawing of Timing Rod Brace 42 Design of a Variable Compression Internal Combustion Engine

Figure 25: Drawing of Cylinder

43 Design of a Variable Compression Internal Combustion Engine

Figure 26: Drawing of Crank Case Cover 44 Design of a Variable Compression Internal Combustion Engine

Figure 27: Drawing of Timing Assembly Cover 45 Design of a Variable Compression Internal Combustion Engine

Figure 28: Drawing of Crankshaft 46 Design of a Variable Compression Internal Combustion Engine

Figure 29: Drawing of Crankshaft Counterweight and Wrist Pin 47 Design of a Variable Compression Internal Combustion Engine

Figure 30: Drawing of Cylinder Nut 48 Design of a Variable Compression Internal Combustion Engine

Figure 31: Drawing of Cylinder Nut Shaft 49 Design of a Variable Compression Internal Combustion Engine

Figure 32: Drawing of Cylinder Head 50 Design of a Variable Compression Internal Combustion Engine

Figure 33: Drawing of Valve Cover 51 Design of a Variable Compression Internal Combustion Engine

Figure 34: Drawing of Camshaft Connector Cover 52 Design of a Variable Compression Internal Combustion Engine

Figure 35: Drawing of Camshaft Connector 53 Design of a Variable Compression Internal Combustion Engine

Figure 36: Drawing of Camshaft 54 Design of a Variable Compression Internal Combustion Engine

Figure 37: Drawing of Timing Rod 55 Design of a Variable Compression Internal Combustion Engine

Figure 38: Drawing of Piston Rod

References

Crouch, C., Fagen, A. P., Callan, J. P., & Mazur, E. (2004). Classroom Demonstrations: Learning Tools or

Entertainment? American Journal of Physics(72). American Association of Physics Teachers.

doi:10.1119/1.1707018

Delprete, C., Pregno, F., & Rosso, C. (2009). Internal Combustion Engine Design a Proactical

Computational Methodology. SAE International Journal of Engines, 2, 263-270.

Engineers Edge. (n.d.). External ACME Thread General Purpose Sixe Table Chart. Retrieved from

Engineers Edge: https://www.engineersedge.com/hardware/external_acme_thread_13360.htm

Honda. (n.d.). OverHead Valve Engines (OHV). Retrieved from Honda Engines: http://www.honda-

engines-eu.com/ohv

How a 4-Stroke Engine Works. (n.d.). Retrieved from Briggs and Stratton:

https://www.briggsandstratton.com/na/en_us/support/videos/browse/4-stroke-theory.html

Lee, K. (2018, 4 11). Here's What 'Compression Ratio' Actually Means and Why it Matters. Retrieved

from Jalopnik: https://jalopnik.com/heres-what-compression-ratio-actually-means-and-why-it-

1819723873

Leinback, C. (2013, 11 16). Quora. Retrieved from Quora: https://www.quora.com/What-different-

types-of-car-motors-engines-are-there-Which-would-you-say-you-like-the-most-and-why-Are-

there-any-interesting-motors-engines-in-development

Nasa. (2015, 5 5). Ideal Otto Cycle. Retrieved from Nasa: https://www.grc.nasa.gov/WWW/k-

12/airplane/otto.html 57 Design of a Variable Compression Internal Combustion Engine

Pohanish, R. P., McCauley, C., & Hussain, M. I. (2016). Machinery's Handbook Pocket Edition: A Reference

Book for the Mechanical Engineer, Designer, Manufacturing Engineer, Draftsman, Toolmaker,

and Machinist. South Norwalk, Connecticut, United States: Industrial Press, Inc.

Proctor, C. L., & Cromer, O. C. (2019). Diesel Engine. Encyclopedia Britannica.

Proctor, C. L., & Cromer, O. C. (2019). Gasoline Engine. Encyclopedia Britannica.

Staveley-O'Carroll, J. (2015, September). The Impact of Classroom Demonstrations and Online

Discussions on Student Achievement. International REview of Economics Education, pp. 46-58.

Taylor, C. F. (1985). Internal-Combustion Engine in Theory and Practice, Volume 2- Combustion, Fuels,

Materials, Design (2nd Editino, Revised). MIT Press.

The Ideal Gas Law. (2019, 6 5). Retrieved from Chemistry - LibreTexts:

https://chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/

Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Physical_Properties_of_Matter/

States_of_Matter/Properties_of_Gases/Gas_Laws/The_Ideal_Gas_Law

The Waukesha CFR Fuel Research Engine. (1980, June). Waukesha. Retrieved from

https://www.asme.org/wwwasmeorg/media/resourcefiles/aboutasme/who%20we%20are/engi

neering%20history/landmarks/50-cooperative-fuel-research-engine-1928.pdf

Ukropina, C. (2014, 12 11). and Gasoline Flash Point. Retrieved from Stanford University:

http://large.stanford.edu/courses/2014/ph240/ukropina2/

University of Windsor. (n.d.). Piston and Piston WIngs. Retrieved from Washington Edu:

https://courses.washington.edu/engr100/Section_Wei/engine/UofWindsorManual/Piston%20a

nd%20Piston%20Rings.htm 58 Design of a Variable Compression Internal Combustion Engine Basshuysen, R., & Schafer, F. (2016). Internal Combustion Engine Handbook - Basics, Components,

System, and Perspectives. SAE International.