GDI System-2 by iaemedu


									         INTERNATIONAL JOURNAL OF and Technology (IJMET), ISSN 0976
 International Journal of Mechanical Engineering MECHANICAL ENGINEERING –
 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME
                               AND TECHNOLOGY (IJMET)

ISSN 0976 – 6340 (Print)
ISSN 0976 – 6359 (Online)
Volume 3, Issue 2, May-August (2012), pp. 346-353
© IAEME:                                           ©IAEME
Journal Impact Factor (2011): 1.2083 (Calculated by GISI)


                                  K. D. Sapate1, Dr. Miss. A. N. Tikekar2
                     Research Scholar, Trinity College of Engineering & Research, Pune.
                      Ex. Assistant Professor, Walchand College of Engineering, Sangli.


         Two-stroke engines are becoming obsolete due to stringent emission norms but it has
 advantages of low manufacturing cost, ease of maintenance, simple, compact, etc. A project of
 electronically controlled gasoline direct injection (GDI) system has been undertaken. In the
 Phase – I, the GDI system has been designed, developed, and tested for its operation. GDI will
 be best option for bringing back this two-stroke technology. Fuel injection system basically
 refers to introduction of fuel into the engine cylinders separately from scavenging air. It is full
 recognized that fuel short-circuiting can be completely eliminated if fuel is injected into the
 cylinder directly after the exhaust port closed. Key to the success lies in to the development of
 high performance injection system. Number of researchers had made attempt to introduce
 mechanically/ electronically controlled fuel injection system adopted by making necessary
 engine modifications.
         The proposed fuel injection system has to provide precise fuel metering, fine atomization
 and good distribution of fuel. Fuel injection period will be controlled by microcontroller
 depending upon operating conditions of the engine, which has sensed by the input sensors. A
 program has been designed in assembly language to control the system. The designed GDI
 system can be found suitable for various applications like grass cutter, mopeds, small generator
 sets etc. The phase -II includes practical simulations of the developed GDI programmes on
 engine set up and measuring the performance. However this second phase is not included in the
 scope of this paper.

 KEYWORDS: Two- stroke petrol engine, GDI, carburetor, ECU.

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

         Two-stroke engines have been in used for sometimes in automotive and stationary
applications since early 1900. The advantages of two-stroke engines are i) lighter, ii) simpler and
iii) less expensive to manufacture. Two-stroke engines also have the potential to pack almost
twice the power into the same space because there are twice as many power strokes per
revolution. The combination of lightweight and twice the power gives two-stroke engines a great
power-to weight ratio compared to many four-stroke engine designs. However due to the short-
circuiting of the fuel before combustion, this has resulted in deterioration in overall performances
especially poor combustion efficiency and high white smoke emission problem. Coupled with
the improvement in the four-stroke engine technology, the former has overcomes the latter in
being the choice for mobile platform applications.
         In order to keep the requirements of the modern two-stroke engines, Vieilledent Edmond
[1]studied and found that the best solution is electronic direct injection, in which injection
duration of about a few milliseconds at high frequencies (from 150 to 200 Hz) is possible. By
adopting the capacitive discharge system energy can be stored slowly for discharging in a very
short time. Author has experimented with this system by using electromagnetic injector and
found that the specific fuel consumption has decreased by 30% compared to indirect mode.
There is not much change in power obtained. The unburned HC emission level has decreased by
a great level.
         Glower and Masaon[2] experimented on small capacity two-stroke scooter engine with
conventional carburettor mode and injection mode along with potentially simple and low cost
stratified charging concept. It is observed that both type of engine produced similar bmep level.
They made a comparative study of engine performance with reference to power and engine
emission and found that performance in both carburettor and injection mode showing significant
hydrocarbon emission reduction, which is about 24% at 4000 rpm to 36% at 6500 rpm.
        Nuti and Pardini from Piaggio [3] made the analysis ranging from conventional crankcase
scavenged engines with mechanically controlled direct solid fuel injection to solutions with
separate scavenging pump with electronic injection units, and from low-pressure injection to air
assisted fuel injection with stratified charge. In the IAPAC (Injection Assisted Par Air Comprise)
low-pressure air spilled from the engine crankcase is enriched with fuel through an electronically
controlled valve. The process does not require an external air pump because the compressed air
used to atomize the fuel is supplied at no expense by the crankcase to a surge tank through reed
valves. An engine crankshaft through a chain drives the valve. Authors compared new develop
IAPAC engine performance with carburetor engine. The IAPAC engine has shown advantage
(35%) and HC reduction (75%) over a wide range of engine operating conditions.
        Giichi, Sato and Iwasa [4]experimented on fuel direct injection system applied to a two-
stroke engine for the purpose of reducing exhaust gas emissions especially exhaust
hydrocarbons. It was observed that fuel injection only, as an alternative to the carburettor, was
not an adequate means for exhaust gas purification. Therefore, a combined throttle and spark
timing control device and a thermal reactor were also adopted. On an automotive injection
engine with a swept volume of 21.7 In3, these changes succeeded in reducing hydrocarbons to 5
ppm and carbon monoxide to 0.21% in the Japanese four-mode test the durability of the thermal
reactor is not yet adequate.

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

        Arout [5] experimented on single cylinder two-stroke S.I. Engine in carburetor mode and
in cylinder injection mode for up to 80% throttle opening. The engine was modified and fitted
with an in-cylinder injector on the head. Fuel is supplied through injector with the help of high-
pressure pump. It was observed that there is a significant reduction in bsfc, unburnt HC and CO
emissions, also the power output of the engine showed an improvement.
        Orbital engine company (OBC) has developed a promising “combustion process” with
the associated electronic control, fuel system and other engine hardware to improve two-stroke
SI engine performance to comply with stringent future emission standards. Two main features
are evident, namely, timed pneumatic direct injection into the combustion chamber and high
level of stratification to eliminate irregular combustion and misfire under partial load.
         Two concepts have been developed. The first consists of an injector in which the fuel is
supplied by a standard magnetic injector, typical of automotive low–pressure type as the main
injector, pressurized air (5to10bar) that is generated by a mechanically driven external
compressor also is supplied. The main coil is then energized and injection begins. Through
modulation of current, the composition of the mixture plume is modulated to ensure good
stratification but in the constraint of an easily ignitable mixture near the spark plug. The second
system is a simplified version particularly suitable for small engine is explained. No air
compressor is provided, and gas is charged into the injector chamber during the compression
stroke, however, the control is electronic.

        Electronic control is being used for effectively controlling the air-fuel mixture and
exhaust emissions. The basic principle of fuel injection is that, at a constant differential pressure,
the amount of fuel injected should be directly proportional to the electronically controlled
injector open time. It will reduce fuel consumption and emission. To place the problem and its
solution in perspective, consider the time allotted for events of the cycle for an engine running at
6000rpm i.e. 100 revolutions per second. The time available for injection mixture formation and
combustion is about 2ms to 3ms which is very small. To achieve special distribution of the fuel
spray velocities must be of the order of 100 meters per second. To vaporize quickly, the droplet
size must be less than 10 to 20 microns at or very soon after leaving the nozzle. The air motion
after closure is relatively small and of the order of piston speed or about 20 meters per second.
The air motion after closure is relatively small and of the order of piston speed or about 20
meters per second. Another constraint the space available for mounting injector is very less. The
air motion after closure is relatively small and of the order of piston speed or about 20 meters per
second. Another constraint the space available for mounting injector is very less. Considering all
above points the electronic fuel injection has been designed. The data required at various
engine operating conditions is obtained by running the engine at full operating range and
accordingly data was collected with reference to different engine parameters like torque, power
and bsfc by connecting carburetor mode engine to eddy current dynamometer. The look up table
for fuel consumption on speed and load basis is formulated for every 500 rpm and is stored in the
microcontroller memory.
       Figure 1 show the schematic layout of the overall fuel injection system developed for the
prototype engine. This is a direct fuel-injection system will be developed as a mean of further

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

improving the engine operational efficiency and is very much in line with the trend of small
engine development program i.e. incorporating an effective fuel dispensing system. Here the fuel
is pressurized by an electrical pump, which is driven by battery. A pressure relief valve is
attached to the high-pressure fuel line to maintain the fuel pressure at 2 to 3.0 bar.
        The sensing units provide signals to microcontroller. A Central Processing Unit (CPU)
interprets these conditions in order to calculate the amount of fuel, among numerous other tasks.
The desired "fuel flow rate" depends on several conditions, with the engine's "air flow rate"
being the fundamental factor. The pulse is applied once per engine cycle, which permits
pressurized fuel to flow from the fuel supply line, through the open injector, into the engine.

Fig.1: Schematic Diagram of Direct Gasoline Fuel Injection System for a Two Stroke SI Engine

        The fuel injector is an electro-mechanical device which meters, atomizes and directly
supplies fuel into the cylinder based on signals from the controller. The injector is installed with
an insulator/seal on the cylinder block/head to isolate the injector from heat and to prevent
pressure leakage of the cylinder. The fuel delivery pipe serves to secure delivery of fuel to the
injector. In a direct fuel injection engine, the fuel must be injected in a short period of time and at
pressures at least 40 times higher than in port fuel injection. As soon as the injector receive
signals from the microcontroller, its needle valve is opened by electrically operated solenoid
valve and fuel injection start with desired spray pattern. An electric solenoid valve in the injector
opens and closes the valve. Fuel sprays out as long as the valve opens. Each opening and
closing of the injector valve is an injector impulse.

       The electronic circuit diagram is shown in Fig.2. The microcontroller AT89C52 is
connected to different auxiliary circuits. Power supply unit is connected to microcontroller to the

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

pin 40. Out of two input sensors, the speed/RPM sensor circuit is connected to pin 12 and throttle
position sensor (TPS) is connected to Port (P1) of microcontroller. Pulse calculations are carried
out by microcontroller based on input signal, look up tables and software program fed to it. The
output pulse signal is given to injector circuit, which is connected to pin 25 of microcontroller.

                Fig. 2: Circuit Diagram of Direct Gasoline Fuel Injection System

Input Sensors:

   The fuel quantity to be injected depends upon many engine input parameters like engine
speed, engine load, manifold absolute pressure, oxygen contents of exhaust gases, throttle
position sensor, engine temperature etc. Following important two engine parameters are
considered for experimentation and they are explained as under.

Throttle Position Sensor (TPS):
        There is a Throttle Position Sensor potentiometer (pot) on the end of the throttle shaft,
and a voltage output (0-5) given to ADC0804 that varies depending upon the position of that
pot. Calibration of the potentiometer is done (0 - 5 volt) with respect to full opening and closing
of throttle valve is carried out before mounting the sensor on the throttle. Intermediate position is
sensed and fed to the microcontroller with respective voltage.

Speed and Crankshaft Position Sensor:

       Engine rpm measurement and exact injection of fuel with reference to crank position is
sensed by speed sensor. A LED (Light Emitting Diode) light source is positioned opposite to a
phototransistor, a chopper plate, in the form of a disc, is attached to the crankshaft shaft. A slot

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME

or hole on the disc allows the light to pass to the phototransistor at the instant when the slot is
aligned with the LED and at this point it signals the position of the shaft. Although this
description suggests a visual light radiation, the system often uses light frequencies beyond the
visible range of naked eye. Voltage is applied to the LED, which is set to give a phototransistor
output. The output is sufficient after amplification to suit the microcontroller. In this, the typical
output voltages will be 2.4 V (high level) and 0.2 V (low level). This type of sensor gives a
square-wave, this makes it compatible with the requirements of a digital system.
        The microcontroller has its input and output in binary form, whereas in our system the
physical quantities measured are in analog form, hence there is a need of interfacing systems of
conversion of analog signal to digital form in-between sensors / actuators and the
microcontroller, the interface system includes:
•       Throttle Position Interface Board
•       Speed Interface Board
•       Injector Interface Board
•       Power Supply to the Entire Board
Software programme is designed with respect to the signals taken from various sensors as input
to microcontroller. Processing is done for different operating conditions. The output of the
program from microcontroller is to control the fuel injection quantity. The details of the program
like flow chart, coding and decoding is not included in this paper.
        Referring to different engine parameters the system is simulated for responses in effective
fuel control and distribution system using special Graphical User Interface (GUI) based software
(Proteous). It gives variation of fuel quantity with respect to the changes in input parameters like
engine speed and load which can be visually observed as shown in figure 3, Channel 1 indicates
the pulse output and Channel 2 indicates engine rpm. The data obtained is confirmed with
calculations based on carburetor mode performance of the engine.



                    Fig 3: Circuit testing showing injector output at 3000 rpm.

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May August (2012), © IAEME


        In the first phase of experimentation, development of electronic circuit for fuel injection
system is completed. It has been observed that with the developed GDI system, it is possible to
control precise quantity of fuel at all operating range of engine. Therefore, the quantity of fuel
which would waste in scavenging in case of carburetor mode can be reduced. Figure 4 shows the
expected test results of the attained power over the speed range for carburetor mode and injection
mode, low range and high speed range. The incorporation of the fuel injection system will show
improvement in the engine output, particularly for high speed range. The reason may be due to
atomization and vaporization of air fuel mixture while passing through the injector which improves
combustion efficiency. As trapping efficiency is more in this mode, mixture of air fuel retained is more,
which produces more power as compare to carburetor mode.

                   Fig. 4 : Brake power vs. Speed in Carburetor and GDI mode

        Figure 5 shows the graphs of expected brake specific fuel consumption BSFC vs. speed.
                                 mode BSFC would be reduced by about 18 % over range of speed
It is observed that in injection m
from1500 rpm to 4000 rpm.

                         Fig. 5 BSFC vs. Speed Carburetor and GDI mode

International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –
6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 2, May-August (2012), © IAEME


       Even though it is often declared that the two-stroke engine will be legislated out of
existence due to its excessive emissions and high fuel consumption, but the present research has
shown that the re-engineering and retrofitting with a microcontroller will definitely make the
two-stroke engines march along with four- stroke engines.

   1. Vieilledent Edmond, “Low Pressure Electronic Fuel Injection System For Two-Stroke
      Engines”, SAE 780767
   2. Mason Brain Stephen Glower and Brain Mason. , “Evaluation of a Low Emission
      Concept on a 50 cc Two-Stroke Engine”, SAE 951783.
   3. Nuti Macro and Pardini Roberta, “Twenty years of Piaggio Direct fuel Injection Research
      to Mass Produced Solution for Small 2 Stroke S.I. engines”, SAE 980760.
   4. Yamagishi Giichi, Sato Tadanori and Iwasa Hiriyoshi Giichi Yamagishi,, ‘A Study of
      Two-Stroke Cycle Fuel Injection Engines for Exhaust Gas Purification.’, The Automotive
      Engineering Congress and Exposition. Detroit, Michigan, January1972, Paper no.720195.
   5. Arout M.M.Wani, M.K. Gagendre Babu T.J. Bhatti and Vijay Sharma ‘Experimental
      investigation on two-stroke cycle, spark ignition Gasoline direct injection engine’. SAE.
   6. N. John Beck, W.P.Johnson, R.P.Barkhimer and S.H.Patterson of BKM Inc “Electronic
      Fuel Injection for two-stroke Cycle Gasoline Engines”. Paper 8612242 presented at the
      International offway & Powerplant congress & Exposion, Miwaukee, Wisconsin,
      September, !986.
   7. S.Scott Goldsborough and P. Van Blaringan, “ Optimizing the Scavenging System for a
      Two-Stroke Cycle, Free Piston Engine for High Efficiency and Low Emissions: A
      Computational Approach” SAE Paper No.: 2003-01-0001, 2003.


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