Types of fuel injection in SI and CI engines, performance and advantages over conventional

petrol enginesPresented by: Asad Saleem 2014-ME-302

Salman Imtiaz 2014-ME-303

Hannan Hameed 2014-ME-307

Farzad Qamar 2014-ME-336

Contents

• Introduction

• Types of fuel injection systems in SI engines

• Types of fuel injection systems in CI engines

• Advantages of modern Fuel injection methods in SI engines

• Advantages of modern Fuel injection methods in CI engines

Introduction

• All Internal combustion engines require injection of the fuel and air into the combustion chamber to achieve combustion and consequently produce power.

• Both SI and CI engines have different types of fuel injection systems which will be described in detail.

Types of Fuel Injection in SI engines

1. Carburetion

2. Throttle body injection system

3. Multi point fuel injection

1. Carburetion

• Formation of combustible air-fuel mixture outside the combustion chamber by mixing proper amount of fuel and air is called carburetion

• This is done by a device called carburetor

• Appropriate for Petrol 4 and 2 strokes engines as petrol is more volatile than diesel

• Fuel is atomized by relying on the air speed

2. Throttle body injection system

• Similar to carburetor throttle body injection system with a throttle valve controlling the amount of air entering the intake manifold

• Injector is placed slightly above the throttle body

• Injector sprays the gasoline into the air in the intake manifold where gasoline mixes with the air and mixture passes through the throttle valve and enters the intake manifold

• It may be timed or continuous type

3. Multi point fuel injection

• Multipoint fuel injection (also called PFI, port fuel injection) injects fuel into the intake ports just upstream of each cylinder's intake valve, rather than at a central point within an intake manifold.

• 3 types:-

Sequential: Injection is timed to coincide with each cylinder's intake stroke

Batched: Fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke

Simultaneous: Fuel is injected at the same time to all the cylinders

Types of Fuel Injection in CI engines

1. Mechanical injection system

2. Common rail injection system

1. Mechanical injection system

• Fuel is forced into the cylinder by means of compressed air

• Not widely used anymore as it requires bulky multistage air compressor which increases engine weight and reduces brake power output

• Despite that it gives good mixing of fuel with the air resulting in a higher mean effective pressure meaning higher indicated power for the engine

• High viscosity fuels can be injected through this method

2. Common rail injection system

• High pressure pump supplies fuel to a fuel header

• High pressure in header pushes to the respective nozzles located in the cylinders

• At the proper time, a mechanically operated valve allows fuel to enter the proper cylinder through the nozzle

• Length of push rod controls the amount of fuel entering in the combustion chamber

Advantages of modern Fuel injection methods in SI engines

• Uniform distribution in multi cylinder engines

• Higher volumetric efficiency

• Reduced or eliminated detonation

• Formation of ice on the throttle plate is eliminated

• Manifold wetting is eliminated

• Atomization of the fuel is independent of cranking speed and therefore starting the engine will be easier

Advantages of modern Fuel injection methods in CI engines

• Drastically cuts emissions

• Increased fuel efficiency

• Complete control over start and end of injection

• Injection pressure is independent of engine speed

• Variable injection pressure can be set