UWE Bristol Engineering showcase 2015

Ryan Coulthard
MEng Mechanical Engineering
Project Supervisor
Neil Larsen
Small Engine Fuel Injection System Development
Project summary
An investigation has been undertaken into the development of fuel injection system for a small engine.
The chosen system incorporates both mechanical and electrical components; a throttle body and injector housing has been designed, manufactured and
fitted to the Honda GC 160, single cylinder four-stroke engine. The mass of air is measured by a mass-air flow sensor, which via a PIC microcontroller and in
conjunction with a known air-fuel ratio, can calculate the fuel needs of the system, and the relevant opening time for the fuel injector to satisfy the
requirements.
Housing Design
The housing for the fuel injector, throttle valve and mass-air flow sensor was developed successfully. After
defining the specification required, an iterative design process was used over two versions.
The fuel injector bracket had to hold the injector at the correct angle without allowing movement. There is a two
stage hole to fit the dimensions of the injector and a top section to hold it down.
The throttle butterfly valve is elliptical in shape so that it is unable to turn past the fully closed position, a spring
system is included to return to the full closed position after partial opening.
The sensor section has a larger internal bore to create room for the mass-air flow sensor. Like for the fuel injector
a bracket was created to keep the sensor in position and with the correct orientation.
Housing Manufacture
The housing was manufactured by 3D printing in ABS Plastic.
Mass-Air Flow Sensor
PIC Microcontroller
Mass-Air Flow Sensor
The mass-air flow sensor (Left) operates by a hot film process. The sensor
outputs a voltage ranging from 0-5v, the output voltage increases as air flow
increases. To get accurate results the sensor needed to be calibrated, this was
done by passing controllable and measurable air flow, up to 6.67x10 -3 m 3 /s,
through the manufactured housing with the sensor inside. The results were
graphically represented for the range of air requirements for the engine (Right).
The value for mass-air flow in conjunction with the mass air-fuel ration means
the mass of fuel required can be calculated.
PIC Microcontroller
The microcontrollers role is to analyse an input
voltage (output voltage from sensor) and output
an opening time for the fuel injector. At this stage
a choke was introduced to increase output time
by 10%. This was tested by having a controllable
input voltage and seeing if an LED would flash for
the correct relative time. This was a success and
a positive proof of concept with the choke button
also increasing opening time as planned.
Final Assembly
All parts were combined in their intended places
to ensure everything fit as planned. The housing
attached to the engine the sensor was powered
and the PIC received the output voltage.
Unfortunately the engine was not in an
operational condition to run and time was not
available to fix it in time. This meant the system
was never fully operational for its intended
purpose
Final Housing Design Assembly
Sensor Calibration Graph
Complete Final Assembly
Project Objectives
• The correct amount of fuel and air should be
supplied. Depending on the rotational speed of
the engine and the air-fuel ratio, the
requirements change.
• Ease of operation. It should be a simple system to
use; after the engine is started there should be
minimal human input to keep the engine
operating. .The system must be able to change
quantity of fuel injected to adapt to a change in
air mass flow.
• Small size and lightweight. This system is for a
small engine so the developed parts should not
impede on intended usage.
• Relatively cheap. The main reason that
carburettors are preferred in smaller engines is
because of the lower cost to use. The fuel
injection system should be of simple enough
design that its cost is not prohibitive
Project Conclusion
The vast majority of this investigation meets the
initial expectations. All aspects, mechanical and
electrical, have met their aims and specifications.
The only part not area that has not been fully
explored at the conclusion of Part A of the MEng
investigation is that a full demonstration of the
operation for the developed fuel injection system
was not achieved. Due to time constraints and the
engines condition only a complete assembly of the
constituent elements was accomplished.