An Experimental Study for Emission of Four Stroke Carbureted and Fuel Injection Motorcycle Engine

Abstract

Anti-pollution laws in many countries impose a limit on the volume of poisonous gases which may be emitted from a vehicle's exhaust. The aim of this study is to compare the emission characteristic of a carbureted and fuel injection system of a four-stroke motorcycle engine. For this objective, a carbureted engine of Honda Wave 125 cc was converted into a fuel injection system. Emissions of CO, CO2 and hydrocarbon (HC) were measured in the lab. The test was conducted at three different speeds: 2000, 4000 and 6000 RPM; and at two loads: 5Nm and 10Nm. Upon conversion of the motorcycle engine, the results show improvement in term of reduction of emissions of all three gasses. Emission at a 5 Nm load improved by 62.6%, 29.75% and 11.33% for CO, HC and CO2 respectively. The results also showed a similar trend at a 10 Nm load, where the emissions improved to 75.86%, 30.1% and 47.71% for CO, CO2 and HC respectively. The results show that fuel injection is evidently a better system as it delivers lower emissions.

Full text

Journal of Advanced Research in Fluid Mechanics and Thermal Sciences 62, Issue 2 (2019) 256-264
256
Journal of Advanced Research in Fluid
Mechanics and Thermal Sciences
Journal homepage: www.akademiabaru.com/arfmts.html
ISSN: 2289-7879
An Experimental Study for Emission of Four Stroke
Carbureted and Fuel Injection Motorcycle Engine
Adnan Katijan1,*, Mohd Faruq Abdul Latif1, Qamar Fairuz Zahmani1, Shahid Zaman2, Khairuldean
Abdul Kadir3, Ibham Veza3
1
Faculty of Engineering Technology, Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia
2
Depratment of Mechanical Engineering, Institute of Space Technology, P.O.Box 2750, Islamabad 44000, Pakistan
3
Faculty of Mechanical Engineering, Universiti Teknologi Malaysia, 81310, Johor Baharu, Johor Malaysia
ARTICLE INFO
ABSTRACT
Article history:
Received 13 May 2019
Received in revised form 21 September 2019
Accepted 12 October 2019
Available online 27 October 2019
Anti-pollution laws in many countries impose a limit on the volume of poisonous gases
which may be emitted from a vehicle’s exhaust. The aim of this study is to compare the
emission characteristic of a carbureted and fuel injection system of a four-stroke
motorcycle engine. For this objective, a carbureted engine of Honda Wave 125 cc was
converted into a fuel injection system. Emissions of CO, CO2 and hydrocarbon (HC)
were measured in the lab. The test was conducted at three different speeds: 2000,
4000 and 6000 RPM; and at two loads: 5Nm and 10Nm. Upon conversion of the
motorcycle engine, the results show improvement in term of reduction of emissions of
all three gasses. Emission at a 5 Nm load improved by 62.6%, 29.75% and 11.33% for
CO, HC and CO2 respectively. The results also showed a similar trend at a 10 Nm load,
where the emissions improved to 75.86%, 30.1% and 47.71% for CO, CO2 and HC
respectively. The results show that fuel injection is evidently a better system as it
delivers lower emissions.
Keywords:
Carbureted engine; Fuel injection
system; CO2; Hydrocarbon (HC)
Copyright © 2019 PENERBIT AKADEMIA BARU - All rights reserved
1. Introduction
Green technology is the rage these days and many scholars want to contribute towards the
advancement of this technology. One area of concern is air pollution which is something people want
to avoid, with scholars working towards the improvement of air quality. Normally, emission comes
from propulsion systems such as a vehicle engine.
People are now concerned about pollution produced by engines, and as a consequence new
regulation have been put in place. Car and engine manufacturers are obliged to follow these
regulations to avoid being fined by the authorities. A small gasoline engine is defined as an internal
combustion engine (ICE) which has a small combustion chamber whose capacity is measured in cubic
centimeters (cc) ranging from 50 cc to 150 cc. Automobiles in this category include motorcycles,
* Corresponding author.
E-mail address: adnankatijan@utem.edu.my (Adnan Katijan)
Open
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which are popular worldwide as a means of transportation, particularly ones run by a carburetor
system, due to their mobility, convenience, economy and their versatility on different roads. The laws
limiting the volume of poisonous gas emissions make the use of small fuel injection systems a
plausible solution.
The emission legislation of Euro 6C [1], that became effective in Europe in the year 2017
motivated industry players to improve their products, with EFI being one of the technologies that
satisfy the Euro 6C legislation. Earlier, on 2014, the Global Technical Regulation under the United
Nations’ World Forum for Harmonization of Vehicle Regulations was established for eradicating air
pollution [2].
There is no doubt that motorcycles are a major means of transport in Malaysia, as well as in
Southeast Asia. It is estimated that 60% to 75% of all road vehicles in Asia including India, Indonesia,
Taiwan, Thailand and China are motorcycles [3]. Most motorcycles in South East Asia still have
carburetors as the main engine system. Carburetor is unable to hold the mixture of fuel and air close
to the stoichiometric thereby causing the production of more emissions even when a catalytic
converter is installed in the exhaust system. Therefore, it has lower efficiency and high emission
values thereby making it impossible to comply with the prevailing emission legislations [4]. Another
technology such as fuel injection is more advanced compared to this technology.
1.1 Carbureted and Fuel Injection System
The carburetor and fuel injection system has a basic common working theory where performance
is measured in terms of the amount of fuel and fresh air entering the engine cylinders. Both systems
feed fuel and air into the engine. Basic components in the cylinders of both systems are pistons and
combustion chamber wherein the reaction between fuel and air occurs during combustion, thereby
releasing energy. However, there are many differences between the carburetor and fuel injection
with the main difference being the method which fuel is injected. For an engine with a fuel
injection system, the fuel is introduced into the internal combustion engine by using an injector [5].
A fuel injector comprises of a valve-nozzle combination which introduces a spray fuel into the air
flow. The amount of fuel that is injected is calibrated either by solenoid actuation (electronically
controlled) or cam actuation (mechanically controlled) [6]. On the other hand, for carburetor system,
suction is created by an air intake air which accelerates through a venturi tube and draws fresh air
into the combustion chamber.
There are many types of fuel injection such as throttle body injection (TBI), port fuel injection
(PFI), sequential port fuel injection (SPFI) and direct injection (DI). Nowadays, most automotive
engines use port fuel injection, with the increased use of direct fuel injection [7, 8]. Even though a DI
system is more advanced compared to PFI, this study considers the PFI system due to its benefits
over the DI system. The most outstanding benefit of the PFI system is its low capital investment which
differs greatly from the high cost of the GDI, which is also highly complex and strenuous to implement
on a commercial engine. Meanwhile, GDI system has been found to emit higher numbers of
particulates than PFI system [9]. In comparison to a carbureted engine, the injection system requires
a high fuel pressure system. Carburetor operates at a fuel pressure of 0.04 MPa – 0.05 MPa, which is
much smaller compared to PFI which runs between 0.25 MPa to 0.45 MPa while GDI runs between 4
MPa to 13 MPa [4, 10, 11]. Higher pressure means better atomization and penetration of the fuel
which facilitates better mixing before spark occurrence thereby reducing the amount of emission
produced [12].

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1.2 Exhaust Gas Emission
In the experiment carried out in this study, exhaust pollutants (emissions) of the engine, including
carbon monoxide (CO), carbon dioxide (CO2), and unburned hydrocarbon (HC) were investigated at
different engine speeds and loads. Carbon dioxide is directly related to the combustion of fuel and
larger amounts of CO2 in exhaust result in better fuel combustion [13]. However, the maximum
acceptable amount of CO2 in gasoline is 12.62% (value from stoichiometric calculation) [14] . The HC
is mostly caused by an unburned fuel–air mixture. Carbon monoxide (CO) is a by-product of the
combustion of rich fuel–air mixture, which is as a result of inadequate oxygen to fully burn all the
carbon in the fuel converting it into CO2. Lower HC and CO in gas emission from the exhaust indicate
that the engine is in good condition.
A number of studies by previous researches show that a carburetor system produces high
emission compared to a fuel injection system. In studying the amount of pollutants emitted by a
carbureted engine, an experiment was conducted on 60 carbureted motorcycles [15]. Different
engine sizes were tested on a chassis dynamometer for various mileages. The result showed that on
average, the carbureted engine produces seven times the allowable limit of CO emission set by the
Euro-3 certification. Stahman and Rose [16], in their emission study of the differences between
carbureted and fuel injected engines found that the use of fuel injection engines could help reduce
CO emissions by 50 to 60 percent, while HC emissions could be reduced by 25 to 50 percent. The
revelations made by these studies on the high CO pollutants released in the air were the reason
behind the replacement of the carburetor with the fuel injection systems in the 1970s.
2. Methodology
Honda Wave 125 cc motorcycle has been used for this study. As shown in Table 1, the engine is a
four-stroke, single-cylinder and naturally aspirated engine. In this experiment, the carburetor has
been replaced with a fuel injection system. During installation, some of the parts, such as the bracket,
have been re-designed and fabricated so as to be able to support the new system. The engine setup
along with the test cell which constitutes of an appropriate data acquisition system, are shown in
Figure 1.
Table 1
Engine Specification
Parameter
Value
Engine Type
4-Stroke, OHC, Air Cooling, Carburettor
Maximum Torque
10,00 Nm @ 5000 RPM
Cylinder Bore
52.5 mm
Stroke
57.9 mm
Air Cleaner
Paper Core Filter Type
Ignition System
CDI
No of Cylinder
1
Starter
Kick-starter and electric
Transmission
4 Speed
Displacement
124.9 cc
Compression Ratio
9.3 : 1
Maximum Power
9,10 HP (6,6 kW) @ 7500 RPM
For the engine conversion, this study utilizes a standard EFI kit which is illustrated in Figure 2. The
system has ECU and a complete throttle unit made up of a throttle sensor and an injector as its main

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components for controlling the fuel. Other than that, an external fuel system has been installed on
the system comprising of components such as a fuel tank, fuel pump, fuel regulator and fuel filter, all
of which are assembled together as shown in Figure 3. For better combustion of fuel, the system
requires a fuel pump that can produce enough pressure during combustion. For this reason, a pump
that has a pressure of 300kPa and flow rate of 25L/hr has been selected. Additional specifications are
presented in Table 2.
Fig. 1. DYNOmite Dynamomete
Table 2
Fuel Pump Specification
Pump Types
Value
Supply Voltage
12V DC
Working Current
< 2A
Pressure
300kPa
Flow rate
25L/hr
Working temperature
-40°C - 80°C
ECU needs a power supply for its operation, however, it cannot be directly connected to a
motorcycle battery because this can drain battery power faster. For this reason, the ECU is connected
to the ignition switch for power supply. By doing this, power is supplied to ECU only if the engine is
ON. This can potentially save battery power. Originally, the fuel pump was powered by a 12V battery
through two terminal connectors,: positive and negative. However, due to the possibility of a high
load during engine high speed and instability of power supply, the design was changed. Instead of
connecting the fuel pump to the motorcycle battery, it was directly connected to the external power
supply through two terminals. The ECU is connected to the engine plug cable so as to facilitate the
measurement of the engine’s speed.

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Fig. 2. Engine conversion
Exhaust gas was measured using gas analyzer which is part of DYNOmite Dynamometer system.
DYNOmite Dynamometer can measure 5 different types of gases: O2, NOx, CO, HC and CO2 as well as
measure AFR (airflow ratio). However, for purposes this study, only three gasses were measured:
CO2, CO and HC.
Fig. 3. Fuel system assembly
In this study, for better data consistency, measurements were read 5 seconds after placing a gas
probe in the exhaust (Figure. 2). Engine temperatures were allowed to stabilize at each test condition
before data was collected. During the experiment, engine temperature was checked and controlled
using an infrared thermometer.
Different RPMs and loads were set for each of the required readings. During the test, the gear
was set at 4, which is the higher gear ratio for this motorcycle. The test was made in the steady state

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which means speed is constantly set at 2000, 4000 and 6000 for a specified brake loading at 5 Nm
and 10 Nm. Emission reading for both carbureted and fuel injection system was measured while the
motorcycle was placed on the dynamometer.
The aim of the experiment was to compare the measurements of a carbureted system versus a
fuel injection system. Both systems were subjected to the same test method and procedures. Before
the measurements were read, the fuel injection system was tuned to its maximum performance
which point the air-fuel ratio of the system is set to a value close to the stoichiometric ratio. The ratio
was subsequently read using a gas analyzer.
3. Results
3.1 Emission Measurement at a Load of 5 Nm
Figures 4 and 5 illustrate the variation of CO, CO2 and HC emissions in accordance with speed
changes at a load of 5Nm for both carbureted and fuel injection engines. For both systems, it is
evident that the amount of CO2 emission increases with a rise in engine speed. Conversely, the
amount of HC emissions, decreases when engine speed is raised. The figure clearly shows increasing
quantities of CO2 and declining quantities of HC for carbureted and fuel injection systems at varied
engine speeds. Stoichiometrically, hydrocarbon fuel combustion should generate only CO2 and water
(H2O).
A study by Monasari et al., [17] on the analysis of gas emissions and fuel consumption on the SI
engine, it was found that as the engine rotation increases, the CO2 emissions increase. The study
stated that the amount of CO2 in the exhaust indicates the occurrence of a complete combustion
process. In a previous study on the 1.4i SI engine by Ozsezen, it was brought to light that unburned
HC emissions reduced at higher engine speeds [18]. At high speeds, the air–fuel mixture homogenizes
to increase in-cylinder temperature. This condition in turn enhances combustion efficiency. Thus, HC
emission decreases more at high engine speeds than at low speeds [19].
As both HC and CO2 show clear direction of its value, however, CO shows a slight increase in value
from 3.63 to 4.29 for the carbureted engine and 0.5 to 3.11 for the fuel injection engine.
In the event that there is inadequate oxygen to convert all the carbon emitted to CO2, then some
of the fuel remains unburned and is thereby released as CO. Larger quantities of CO are generated
when an engine is accelerating at high speed [20]. Even in situations where the intake of the air-fuel
mixture is isometric or minimal. some CO will be generated in the engine.
Fig. 4. CO and CO2 measurement at load 5 Nm
3.63 4.22 4.29
6.10
8.83
10.29
0.50 1.03 3.11
7.25 9.55
11.51
0
2
4
6
8
10
12
14
2000 4000 6000
CO & CO2 (%)
Engine Speed (RPM)
Carburetor : CO Carburetor : CO2
FI : CO FI : CO2
2
1
2
3
4
1
3
4

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Fig. 5. HC measurement at load 5 Nm
The experimental results in this study show that both systems produce different quantities of gas
emissions and that a fuel injection systems much better than a carbureted system [16]. A comparison
of the performance at speeds of 2000, 4000 and 6000 shows that, the quantity of CO emissions
reduced by 86.2%, 75.6% and 26.1% respectively. Therefore, this translates to an average
improvement of 62.6% at all three set speeds. The results also show a similar trend in HC emissions,
which show an average reduction of emission by 29.75% while CO2 emissions improved by 11.33%.
A better combustion process which utilizes a fuel injection system results in reduced emissions
of HC, CO and CO2. The fuel injection nozzles used in the new system facilitate breaking down of the
fuel into very fine particles, which easily vaporize during the induction process [16]. This process
improves homogeneity of fuel injection.
3.2 Emission Measurement at a Load of 10 Nm
Figure 6 and Figure 7 illustrate the variation of CO, CO2 and HC emissions in accordance with
speed variations at a load of 10 Nm for both carbureted and fuel injection engines. Both results at a
load of 5 Nm and 10 Nm show similar trends in their results; the quantity of CO emissions increases
with a rise in engine speed. Meanwhile, when engine speed is raised in a carbureted engine, the
quantity of CO2 emission increases but the amount of HC emissions decreases.
Fig. 6. CO and CO2 measurement at load 10 Nm
328.00 297.10
200.37
300.25 286.56
45.56
0
50
100
150
200
250
300
350
2000 4000 6000
HC (ppm)
Engine Speed (RPM)
Carburetor : HC FI : HC
4.36
5.29 6.16
6.10
8.75 9.70
0.21 0.54
3.53
11.30 11.60
12.11
0
2
4
6
8
10
12
2000 4000 6000
CO & CO2 (%)
Engine Speed (RPM)
Carburetor : CO Carburetor : CO2
FI : CO FI : CO2
2
3
4
1
2
3
1
2
1
2
1
4

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Fig. 7. HC measurement at load 10 Nm
A comparison between carburetor and fuel injection systems, at speeds of 2000,4000 and 6000
show that, CO emissions reduced by 95.1%, 89.79% and 42.69% respectively. Therefore, this
translates to an average improvement of 75.86% at all three set speed. CO2 and HC emissions
improved by 30.1% and 56.42% respectively.
Comparing Figure 5 to 7, it is clear that, at same speed the HC, CO and CO2 increase as the load
increases. This is due to more fuel is introduced to achieve the desire engine torque and hence it
leads to increase in emission [21] .
Compared to the carburetor, the fuel injected engine combustion process is significantly much
more efficient. Precise fuel delivery by an injector along with the mixing of the air and fuel ensures
maximum possible fuel efficiency. As a consequence, fuel economy is maximized while the emission
level is minimized.
4. Conclusions
The conversion of a motorcycle engine from a carbureted system to a fuel injection system was
done in this study, followed by an experimental exercise as specified speeds and load conditions for
each of the systems. The results of the study lead to the conclusion that a fuel injection system is
better than a carbureted engine. This is because the injection system, which is more advanced, has
more effective fuel control than carbureted system. Despite the existence of the carburetor for the
past century, this study proves the superiority of the fuel injection system in producing lower
emissions.
Acknowledgement
The first author would like to express his appreciation to Universiti Teknologi Malaysia (UTM) which
provides technical support and good facilities during this project. Thanks also to Universiti Teknikal
Malaysia Melaka (UTeM) for financial support during his study in UTM.
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