interim report - group #3

8/7/2019 Interim Report - Group #3

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GROUP #3

Interim Report

Direct Injection EngineMitchell Tracy

Blair Kent

Tianya Shao

Irene Wang

Ahmad Chaaban

Clayton Bell

12/21/2010


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Executive Summary

At the end of September 2010, group number three set out to convert a four stroke

engine into a direct injection two stroke engine with central oil. There are a number

of benefits received by conduction this conversion; the most notable benefits

include: lowered release of unwanted emissions when compared with a standard

two stroke engine, a decrease in fuel consumption when compared against a

standard two stroke engine, and an increase in power to weight, or displacement,

ratio when compared to a standard four stroke engine.

The decrease in emissions is a result of the newly converted two stroke engine

having a more efficient process where fuel is not allowed to escape the chamberduring the cycle, as it is on a regular two stroke. The major reason for the decrease

in emissions however; is the absence of oil mixed in with the fuel supply. The oil is

regularly used in two stroke engines to lubricate the cylinder and has an undesirable

byproduct of having oil combusted and released to the atmosphere as gases. Using

central oil and fuel injection the new engine is able to end these two unwanted

aspects of a two stroke engine. By making the engine combust every stroke, as

opposed to every second stroke like a four stroke engine, it is effectively doubling

the power to displacement ratio the engine sees. This is very desirable in many

situations where you have space constraints or weight constraints.

Many alterations must be done to successfully convert the engine into a two stroke

fuel injected engine with central oil, and all of these are currently underway. The

exhaust port has to be made to open twice as often, a new air intake port will need

to be constructed, and an opening for the fuel injector will be created. These

problems are all being solved with mechanical solutions. It is also necessary to make

the fuel injector fire at the correct time; to do this installing an engine position

sensor and connect it to a microcontroller, which will interpret the sensors signal

and in turn, send the fuel injector a signal of its own directing it when, and for how

long, to inject its fuel, is crucial. The above electrical facets will require circuit

building and coding to complete their aims.

Construction of the project is well underway; each aspect of the engine conversion

has a plan which is being acted upon to complete the engine conversion on

schedule.


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Contents

Executive Summary ................................................................................................... ii

List of Figures ............................................................................................................ 4

List of Tables ............................................................................................................. 4

Project Overview ....................................................................................................... 5

Exhaust ..................................................................................................................... 7

Air Intake................................................................................................................... 8

Fuel Injector ............................................................................................................ 10

Electrical ................................................................................................................. 11

Schedule ................................................................................................................. 14

Budget .................................................................................................................... 14

Summary ................................................................................................................. 16

Appendix A ......................................................................................................................18


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ListofFigures

Figure 1 .................................................................................................................................6

Figure 2 .................................................................................................................................7

Figure 3 .................................................................................................................................8

Figure 4 .................................................................................................................................9

Figure 5 ............................................................................................................................... 12

Figure 6 ............................................................................................................................... 14

ListofTables

Table 1 ................................................................................................................................ 15


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Project Overview

The earth is a finite world; a world where resources are limited and where seemingly

inconsequential changes have drastic consequences when carried to the extremes

that the harmonious actions of billions of people often produces. In this world, it is

becoming more and more essential to design more efficient systems; not only for

social and environmental reasons, but increasingly for economic reasons as well.

The need for a system to consume less while producing the same, if not more,

output, is universal. There is also the need to produce less unwanted byproducts;

because they are, in effect, inefficiencies.

Group three is converting a four stroke engine into a two stroke, fuel injected enginewith central oil to meet the needs of earths societies and races.

By adding fuel injection to a two stroke engine a number of the inefficiencies, of a

normal two stroke cycle, are being reduced or eliminated. A regular two stroke

engine has a mixture of fuel, oil and air. This mixture, as seen in Figure 1, is allowed

to enter the chamber at the same time as the exhaust port is open. This looks to,

and actually does, allow un-combusted fuel and oil to leave the exhaust before ever

having the opportunity to be combusted. This wastefulness is corrected by group

threes new design and by injecting the fuel into the chamber at a point in the cycle

when no ports are open.


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Figure 1

The usual two stroke design must mix oil in with its fuel to lubricate the piston. This

oil, once burned, is a major source of pollution and the new design will address this

by using central oil for lubrication. Central oil is a system which basically has an oil

reservoir at the bottom of the cylinder which gets splashed around and lubricates

the cylinder walls and the crankshaft. By using this method of lubrication instead of

mixing the oil with the fuel oil is no longer being burned with the fuel, decreasing

the pollution by a large amount.

To accomplish the goal of converting a four stroke engine into a two stroke fuel

injected engine with central oil alteration of a number of things simultaneouslyon

the regular four stroke engine was needed. Because the 4 stroke engine is being

made to combust twice as often there is exhaust in the cylinder twice as often. This

exhaust has to leave the cylinder in order to make room for new air and fuel to enter

and keep the cycle running. In order to make it possible for the exhaust to leave the

exhaust port will need to be opened twice as often. Another hurdle that had to be

overcome was ensuring clean air is in the cylinder to facilitate the chemical reaction

of combustion. The air also needed to enter the system twice as often due to having

twice as many combustions as usual. A fuel injector must be installed in order to

insert fuel into the system. It also had to be timed accurately to deliver the fuel, in

the right amount, at the right time. An electrical sensor was also required to instruct

the fuel injector when to introduce the fuel. A circuit needed to be designed to


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transfer the signal from the sensor to the fuel injector and a microcontroller was

introduced to calculate the exact time that the fuel injector must fire.

As the previous paragraph explains, there are many components to this ambitious

project. Each component is of vital importance to the overall performance of the

engine and each compliments each other. With this in mind group three split up

into sub-groups which focused on particular parts of the project individually; while

constantly cooperating with other sub-groups to ensure integration and unity in the

project as a whole.

Exhaust

Making the exhaust port open twice as often is a very well defined outcome;

however, it is not as straightforward as it sounds. There are essentially two ways of

accomplishing this; the first is to design a new camshaft (as seen in Figure 2) where

you add another lobe on the camshaft exactly opposite to the existing exhaust lobe.

The new lobe will open the exhaust port the same way as the existing lobe just in a

different part of the cycle.

Figure 2

The second way of making the exhaust port open twice as often is to change the rate

at which the camshaft rotates. This can be accomplished by a number of methods,

but the most straightforward is to change the gear ratio of the gears which drive the

camshaft from the crankshaft. By making a new gear with half the diameter the

camshaft will have twice the rotations per time; directly making the exhaust valve

open twice as often. It was decided to change the gear ratio to accomplish the


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above-stated goal. This decision was made through talking with the machine shop

and being told that they could not manufacture a new camshaft or alter the existing

one.

In order to make the camshaft spin twice at twice the rate a gear with half the

diameter was required; unfortunately the gears connected to the camshaft with bolt

holes at a radius larger than the required radius of the new gear. An adaptor

cylinder was designed to connect the new gear with the camshaft. To date, a CAD

drawing of the new gear and the adaptor cylinder has been assembled and will be

submitted to the machine shop for production soon. Once the part is manufactured

replacement of the current gear with the new part can be achieved. This is a

requisite to manually rotate the engines crankshaft to test if it opens the exhaust

port properly.

Air Intake

The original four stoke engine had an intake port at the top of the chamber which

would allow air and fuel to enter the chamber (an example is shown in Figure 3). As

a result of the changes group three is making on the engine this system will no

longer work with the new engine cycles and cannot be adapted easily to be made to

work.

Figure 3

Clean air must enter the chamber every cycle before the fuel injector inputs the fuel

for combustion. After deciding that adapting the existing air intake system would

not fit theprojectsneeds,the only other option was to create a new air intake port.


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The new port, in order to keep it simple and effective, is to be drilled into the side of

the cylinder. The new port will be low enough so that for the majority of the stroke

the port is covered by the piston and no air can enter or exit the chamber. A good

visualization is provided below, as Figure 4.

Figure 4

Group three has calculated the exact height require to allow air to enter the cylinder

at the correct time in the engines stroke (these calculations can be seen in Appendix

C). Flow calculations have also been completed and are in Appendix C; these

calculations were used to figure out the diameter of port needed in order to have

enough flow to push out the exhaust gases, through the open exhaust port, and to

have the correct amount of clean air in the chamber for combustion. The port must

capable of delivering 100cc of air at an engine speed of 3000 rpm. The port will also

feature a simple valve to control the flow of air through it; this will be used to

change the air flow rates when the engine is running at different RPMs. In order to

gauge how much air is being put into the cylinder an airflow sensor will be placed on

the inside of the air intake port. Once this port is drilledalteration can only occur by

making it larger. As a consequence the first drilling may result in a smaller than

optimal port diameter; by testing the combustion efficiency it can be determined if

more air is needed in the reaction and he port diameter can be altered as needed.


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Fuel Injector

The whole project is centered on installing a fuel injector and claiming the benefits

from the alterations to the engine that must be made to have the fuel injector work

properly. The fuel injector must breach the inner surface of the cylinder and mustbe near the top of the chamber so the piston does not contact the tip of the fuel

injector during its stroke. After taking apart the engine and looking at the physical

places the fuel injector can be placed group three had two options; the first option

was to attach the fuel injector in the same place as the old fuel intake port was

previously, the second option was to drill a hole through the side of the cylinder,

near the top, and attach it with some mechanism. The first option proved undoable.

The shape and contours of the fuel intake port were not suitable for implementing

an attachment of the fuel injector. The second option, to drill a new hole, was

hindered by heat transfer fins which cover the side of cylinder. These fins wereground off to a flat surface to allow for the hole to be drilled in. The way to attach

the injector is still being formulated. Options include attaching an adaptor plate to

the fuel injector and welding it onto the side of the cylinder, making an adaptor

plate which has a thread and corresponds to a thread drilled into the hole on the

cylinder, and bolting the adaptor plate onto the side of the cylinder.

Once the fuel injector is mounted testing will be able to commence. Testing will

occur by connecting the fuel injector to the microcontroller and electric circuit to tell

it when to inject fuel.


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Electrical

The electrical components of this project are all involved with timing. Timing is a

major issue since even at a relatively low RPM the entire engine cycle time is in the

millisecond range. When you take the time constraint into account the electrical

systems must react in the microsecond range in order to complete their tasks in

time to enable the engine to function. The piston turns its crankshaft and the

crankshaft completes a full rotation in the same amount of time it takes the piston

to complete a full cycle. By attaching a sensor to send a signal when the crankshaft

is at a certain point in its rotation, deduction of the pistons corresponding location in

its cycle will be possible. This information is invaluable and will be used to identify

when to inject the fuel for combustion. By attaching a microcontroller to the sensorit can be programed to receive the sensors signal and output a response to the fuel

injector which, having received the response from the microcontroller injects fuel to

the chamber just in time for it to be compressed and combusted when the spark

plug fires.

A microcontroller was chosen instead of designing a solid circuit to output instantly,

when the sensor has been activated, to the injector because of the data

accumulation and manipulation ability a microcontroller provides. A programmable

microcontroller also gives some leeway when physically placing the sensor; if the

sensor is not in exactly the right spot the program can be altered to account for the

timing difference. If, however, just a circuit is used the misplacement of the sensor

would result in a misfiring of the fuel injector. The microcontroller that was chosen

is the Arduino Mega 2560, a picture of the Arduino is shown below in Figure 5. The

Arduino was chosen because of its general use relatively low expense and low

complexity. The other microcontroller being considered was the MPC 555, this

microcontroller turned out to be much too expensive and complex for the projects

needs.


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Figure 5

The electrical signal the fuel injector intake needs to be around 3.8 Amps of currentin order to be recognized; however, the microcontroller outputs a 40 to 50 milliamp

signal. In order to convert the microcontroller output into an acceptable current for

the fuel injector an operational amplifier will be utilized. The microcontroller

receives an input from the sensor. The sensor works by changing its resistance and a

comparator circuit has been designed which will turn this resistance change into a

readable voltage signal. The microcontroller will be programmed to take the voltage

signal and read the signal as information regarding where the piston is in its cycle.

A solenoid driver, which contains a transistor as its main component, was initially

mentioned by Dr. Dunford as a way of controlling the solenoid within the fuel

injector. Another option to achieve the same results, which was suggested by

someone with practical experience, was to use a single transistor to drive the

solenoid. A solenoid driver is a much more advanced tool than is required for this

task and a transistor is capable of achieving the same result. Another factor in

choosing the transistor over the solenoid driver is the transistor only costs 1 dollar

compared to a premade solenoid driver which costs 15 dollars. Transistors require

more circuitry to be designed as they cannot dissipate the energy that is put out by

the solenoid when it is turned off and an electromagnetic field is created by the

solenoid closing. If the transistor turns out to be insufficient for driving the solenoid,

a solenoid driver can be installed anytime since the circuit connecting

microcontroller and the solenoid is not complicated.

With a RPM of 3000, a complete engine cycle takes 20 milliseconds, that gives a

small window to accurately sense where the piston is and inject fuel into the


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chamber. Once all the electrical circuits and programming is in place it will be

possible to test the functionality by using a wave generator to measure the delay

between the sensor output and the microcontroller output. Completing this test is a

crucial step in the progress of the project. If this test does not get completed thereis no way to confirm the electrical mechanical system will work within the time

scales required.


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Schedule

Figure 6, shows a Gantt chart of group threes current schedule. This schedule is

malleable and is continuously being updated as progress gets fast-tracked or

delayed. Currently group three is on schedule and has completed all the tasks

labeled as completed on the Gantt chart below.

Figure 6

Budget

Table 1, is the projected budget to complete this project. The Fuel Injector, Fuel

Pump, and Microcontroller have all been purchased. Every other item in the table

has been priced and is ready to order.

Table 1.

Fuel Injector (Purchased) $100

Fuel Pump (Purchased) $30

Microcontroller (Purchased) $70

Other Electronics $30

Engine Position Sensor $30

Mass Airflow Sensor $100

Gasket Set $10

Total $340


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Group three has a total available budget of $500; if no unforeseen items are needed

the project should be completed from for $340, leaving a difference of $160 unused.

It has been possible to stay so far under budget because one of the group members

already had an unused four stroke engine to donate, and he was also able to usepersonal contacts to obtain a vastly discounted fuel injector.


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Summary

The process of converting a four stroke engine into a two stroke engine with fuel

injection and central oil is well underway. Group three is making progress towards

its final objective and is currently on schedule. Each component of the project is

underway simultaneously, with different sub-groups working on different

components and collaborating together to complete the ambitious aims set forth.

The exhaust system is well understood and is purely a mechanical problem and is

receiving a mechanical solution. By changing the gear ratio it is possible to make the

camshaft spin twice as fast. Doubling the angular velocity of the camshaft has a

consequence of opening the exhaust port twice as often. Since the camshaft is

directed by the crankshaft which is spun by the piston the timing is only dependenton the accuracy of manufacturing of the new gear.

The air intake port has been designed using fluid mechanics equations and has been

calculated to input a desired amount of air to vacate the exhaust gases and to

provide the chamber with clean air to be combusted. The placement of this port is

crucial to the both of these tasks. Having the piston covering the intake port for the

majority of the engine stroke has the consequence of blocking all clean air from

entering; when the piston reaches the bottom of its stroke it exposes the intake port

and allows clean air to enter the cylinder. While the physical drilling of the port is a

simple affair, it is crucial that it be placed at the correct height. If the location is

wrong it will no longer be conceivable to patch and drill another hole.

Mounting the fuel injector is another important development in the engine

conversion. Because another physical hole must be drilled, it is crucial to get it right

the first time. The exact location is not as important as the air intake port but it

must be fastened and sealed so it cannot let any pressure escape during combustion

and must not shake loose due to the vibrations of the engine when it is in operation.

A microcontroller has already been purchased, a sensor has been selected and is

ready for order and the amplification circuit is designed. The electrical aspect of the

project is progressing in parallel with the project as a whole. The electrical

components are responsible for the timing of the fuel pump and are a crucial piece

in this project. Because a microcontroller is being used it is possible to tweak the

timing once everything has been installed and this admission seems a likely scenario;


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which is one of the major reasons to design the electrical system around a

microcontroller instead of a standard circuit. Once all the pieces are together

testing can begin and response times and signal timing can be played around with.

On schedule and under budget group three continually strives to meet the challenge

placed before it. As group three goes into the Christmas break it will continue to

make advances towards the final product, a two stroke engine with fuel injector and

central oil.


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AppendixA

Simple circuit for TIP 122 Transistor

3D view of TIP 122 Transistor

Here are some assumptions I made:

Input voltage (VB) =3.3V (from our microcontroller datasheet)

IB = 0.04A

IC =3.8A

If we assume VCC = 5V, VBE =0.7V

Then we can simplify the calculations:


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VB = (VCCR2)/(R1+R2); 0.66= R2/(R1+R2)

= IC/IB = 3.8/0.04 = 95

IE = IB +IC = 0.04+3.8 =3.84A

IC = (VCC VE )/RC ; VE = IERE

R2 = (VE + VBE)/(10IB)

R1 =( VCC (VE +VBE))/(11IB)

RE =VE /IE

Then we can find the values for the resistors.

The two capacitors are used to prevent current from flowing into input device.

Calculations for TIP 122 Transistor Circuit

Assumption Formula

VB 3.3V (VCCR2)/(R1+R2)

VCC 5V

VBE 0.7V

VE IERE

IB 0.04A

IC 3.8A (VCC VE )/RC

IE IB +IC

R2 (VE + VBE)/(10IB)

R1 ( VCC (VE +VBE))/(11IB)

RE VE /IE

RC (VCC VE )/ IC

(HFE) IC/IB


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Appendix B

Piston Displacement vs. Time


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Appendix C

For an air intake at bottom of stroke with same opening characteristics as exhaust, need todetermine size of hole.

With angle of 65 degrees at bottom of stroke.

L = r + x - 2 r x cos (angle)

L = rod length of 107mm

R = radius of crank = engine stroke = 24mm

Angle is between 147.5-212.5 degrees (measured from the top of stroke)

This equation will define the top and bottom of stroke and the difference between the

position at bottom and the position at 147.5 or 212.5 degrees.

Diameter of hole = 3.56mm

Source :

http://upload.wikimedia.org/wikipedia/commons/3/36/Piston_motion_geometry.png

Approximations of pressure required.


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A = pi (diameter of hole)/4

v=Q/A and Bernoulli eq. v/2 + gz + P/p = constant

v = velocity

Q = volumetric flow rate

A = cross section of intake

z = height difference = 0

P = pressure difference

p = density = 1.3 kg/cubic meter

Q = V/t varies with rpm and desired throttle

V=volume of air to be delivered into cylinder, ratio of 14.4 by mass to fuel put in. At max

throttle V = 110cc, t = 65/360 * (Rev/min / 60)

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