Thesis Abstract

The thesis is aimed at designing a fuel atomizer device to be incorporated in a fuel economizer system for use in petrol engines for more efficient fuel consumption. The principle adopted is based on the spraying paint machine. A compressor is used to compress air from the atmosphere and deliver it to the carburetor. The power required to operate the compressor is obtained by connecting the compressor pulley and the crankshaft pulley with a fan belt. A fuel atomizer device is used to ensure that correct orifice released air to the carburetor with the aid of control valve and air pressure gauge to ensure that correct air/fuel ratio is maintained. An air dryer is installed to absorb moisture from the air. An air cylinder is installed to store compressed air, while a high pressurized air incorporated inside the carburetor through a pipe and atomizer device’s orifice to atomize fuel into tiny possible particles to achieve a complete combustion and fuel economy. This was ascertained by testing vehicle with fuel economizer with measured quantity of fuel, noting the speedometer at the start of the vehicle for a certain distance and doing the same without a fuel economizer. The speedometer and time taken were recorded and graph of the result was shown in figure 4.20. The result showed that vehicle installed with fuel economizer device gives complete combustion than vehicle without it. It also reduces petrol waste, lessens pollution and installation is environmental friendly.

 

Thesis Overview

INTRODUCTION

 

 

1.1       BACKGROUND OF THE RESEARCH

The fuel atomizer system in petrol engine is a designed mechanism for reducing the rate of fuel consumption and obtaining a complete combustion process in a petrol engine. Some companies introduce fuel injection system method of delivering fuel to internal combustion engine. Car designers such as BMW, Mercedes Benz and Volvo have incorporated different designs to improve fuel economy in cars.

Modern computerized fuel injection produced more power, lower exhaust emission, improved fuel economy than other carburetor systems. However, the following factors affect the process of carburetion:

• Time: The higher the engine speed, the lesser time is available for mixture formation.
• Temperature: A higher temperature of mixture improves vaporization of fuel and mixture quality and consequently, increases indicated efficiency of the engine.
• Design: The design of the carburetor with its elements, heating system for mixture, shape and cross-sectional area of intake pipe, and the shape of the combustion chamber have good effect on the uniform distribution of the mixture among the cylinders and in various operating conditions of the engine.
• Quality of Fuel: The greater the carbon contents in hydrocarbon the less volatile the fuel as stated in the table 1.1 below.

 

 

 

 

 

Table 1.1: The physical properties of the first twenty members of straight-carbon alkanes

Number of Carbon Atom(s)Molecular FormulaStates(at 25 °C)Melting Point (°C)Boiling Point (°C)Density at 25 °C (g cm-3)1CH4Gas-183-1610.4242C2H6Gas-172-890.5463C3H8Gas-188-420.5014C4H10Gas-13500.5795C5H12Liquid-130360.6266C6H14Liquid-95690.6577C7H16Liquid-91980.6848C8H18Liquid-571260.7039C9H20Liquid-541510.71810C10H22Liquid-301740.73011C11H24Liquid-261960.74012C12H26Liquid-102160.74913C13H28Liquid-72330.75314C14H30Liquid-32600.76115C15H32Liquid102710.76916C16H34Liquid182870.77317C17H36Liquid223020.77718C18H38       Solid283160.77719C19H40Solid323300.78620C20H42Solid373440.785

 

1.2       PURPOSE/OBJECTIVE OF THE RESEARCH

The main purpose of this fuel atomization mechanism is to achieve a complete combustion process in petrol engine 504 Peugeot Station Wagon to achieve a better power output at lowest possible fuel consumption through a tiny fuel atomization. The fuel will be sprayed in small particles which will help the fuel to be in vapour phase to increase complete combustion to achieve this, a higher power output at lowest possible fuel combustion.

1.3       COMBUSTION IN SPARK IGNITION ENGINE

Combustion is a relatively rapid chemical combination of hydrogen and carbon in the fuel with the oxygen in the air, resulting in liberation of energy in the form of heat, thus is exothermic reaction in that heat is given out.

C7H16 + 11O2 + 11N2              7CO2 + 8H2O + 11N2

In spark ignition engine, a carburetor generally supplies a combustible mixture and the electric spark from a spark-plug initiates combustion.

The spark ignition system component sketch in shown in fig. 1.1 below

Fig: 1.1: Spark Ignition System

 

1.4      COMBUSTION PHENOMENON: NORMAL COMBUSTION

In a Spark Ignition (SI) Engine, a single intensely high temperature spark passes across the electrodes leaving behind a thin thread of flame.

From this thin thread, combustion spreads to envelope a mixture immediately surrounding it at a rate which depends primarily upon the temperature of the flame front itself and to a secondary degree upon both the temperature and the density of the surrounding envelope. In the actual engine cylinder, the mixture is hot at rest in highly turbulent condition. The following conditions are necessary for combustion to take place:

• A combustible mixture
• Some means to initiate combustion
• Stabilization and propagation of flame in the combustion chamber

In a fuel injection system, electronically controlled fuel injectors spray measured amount of fuel into each of the engine cylinders where the fuel is burned, powering the engine.

The spread of the flame throughout the combustion chamber is shown below.

 

LNQM assumes compression curve having no ignition

• First stage of combustion, the ignition lag, starts from this point and no pressure rise is noticeable.
• Q is the point where the pressure rise can be detected. From this point it deviates from the simple compression (motoring) curve.
• The time lag between first ignition of fuel and the commencement of the main phase of combustion is called the period of incubation or is also known as ignition lag. The time is normally about 0.0015 seconds. The maximum pressure is reached at about 12o after dead centre point. Although the point of maximum pressure marks the completion of flame travel, it does not mean that at this point the whole of the heat of fuel has been liberated, for even after the passage of the flame, some further chemical adjustments due to reassociation etc, will continue to a greater or less degree throughout the expansion stroke. This is known as after burning (Rajput, 2007).

 

1.5   FACTORS AFFECTING NORMAL COMBUSTION IN S. I. ENGINE

Factors affecting normal combustion in S. I. Engine are:

• Induction Pressure: As the pressure falls, delay period increases; and the ignition must be earlier at low pressure a vacuum control may be incorporated.
• Ignition Timing: If ignition is too earlier the peak pressure will occur too early and work transfer falls. If ignition is too late, the peak pressure will be too low and work transfer will fall. Combustion may not be completed by the time exhaust valve opens and the valve may burn.
• Mixture Strength: Although the stoichiometric ratio should give the best result, the effect of disassociation is to make a slightly rich mixture necessary for maximum work transfer.
• Fuel Choice: The induction period of the fuel will affect the delay period. The calorific value and the enthalpy of vaporization will affect the temperature achieved.
• Combustion Chamber: The combustion chamber should be designed to give a short flame path to avoid knock and it should promote optimum turbulence.

 

1.6     STATEMENT OF PROBLEM

The main problem of this work is to combat the issue of incomplete combustion which encourages unwanted waste of fuel and environmental pollution.

 

1.7     INCOMPLETE COMBUSTION

The incomplete fuel combustion occurs when the oxidizable fuel elements are not oxidized to the ultimate state. Here, there will be excessive waste of fuel (unburned fuel) and it encourages pollution.

 

1.8     DISADVANTAGES OF INCOMPLETE COMBUSTION

There are so many disadvantages that follow an incomplete combustion of fuel.

• DETONATION: is a very sudden rise of pressure accompanied by metallic-hammer sound. The result is tremendously rapid and local increase in pressure which sets up pressure waves that hit the cylinder walls with such violence that the walls emit a sound like a “ping”. It is the ping that manifests detonation.
• SMOG: This is a type of light fog which is unpleasant and a cause of irritation to the eyes and nasal passage. Although not affecting visibility greatly, it does affect vegetation and has caused serious economic loses in horticulture and agriculture.

 

1.9      PRODUCTS OF INCOMPLETE COMBUSTION OF FUEL

The products of incomplete combustion of fuel are: CO, CO2, N2, NO, NO2, SO2, HC and H2O   

 

1.10   LIMITATION

Ignition limit: It has been observed through experiments that ignition of charge is only possible within certain limits of fuel-air ratio.

Combustion Limit:  It is important to note that excess air will be needed for complete combustion.

Ignition timing is important in combustion general limit.

General Limit: No liquid fuel can ignite without being vaporized. Therefore good quality of fuel is important for any combustion. Consequently, calorific value of fuel plays important role in limitation of combustion to avoid explosion

 

RESEARCH METHODOLOGY

This research will consider all the design principles which require the calculation of various parameters. Lastly, it deals with the testing of the fabrication mechanism to evaluate performance.