The document discusses multi-point fuel injection (MPFI) systems for gasoline engines. It describes two main types - port injection and throttle body injection. Port injection involves fuel injectors placed in the intake manifold near each intake port to spray fuel into the air-fuel mixture for each cylinder. Throttle body injection uses a single injector mounted above the throttle body to inject fuel into the incoming air. The document provides diagrams to illustrate the components and operation of each type of MPFI system.

1. MULTI-POINT FUEL INJECTION (MPFI)
SYSTEM
The main purpose of the Multi-Point Fuel
Injection (MPFI) system is to supply a proper
ratio of gasoline and air to the cylinders. These
systems function under two basic
arrangements, namely
(i) Port injection
(ii) Throttle body injection

2. Port Injection
• In the port injection arrangement, the injector
is placed on the side of the intake manifold
near the intake port The injector sprays
gasoline into the air, inside the intake
manifold. The gasoline mixes with the air in a
reasonably uniform manner. This mixture of
gasoline and air then passes through the
intake valve and enters into the cylinder.

3. Port injection

4. Multi-point fuel injection (MPFI) near
port

5. Multi-point fuel injection (MPFI) near
port
• Every cylinder is provided with an injector in
its intake manifold. If there are six cylinders,
there will be six injectors. Figure shows a
simplified view of a port or multi point fuel
injection (MPFI) system.

6. Throttle Body Injection System

7. Throttle Body Injection System
• Figure illustrates the simplified sketch of throttle
body injection system (Single point injection).
This throttle body is similar to the carburettor
throttle body, with the throttle valve controlling
the amount of air entering the intake manifold
• An injector is placed slightly above the throat of
the throttle body. The injector sprays gasoline
into the air in the intake manifold where the
gasoline mixes with air. This mixture then passes
through the throttle valve and enters into the
intake manifold.

8. MPFI-fuel system

9. MECHANICAL INJECTION SYSTEMS
• The fuel-injection system is the most vital
component in the working of CI engines. The
engine performance viz., power output,
economy etc. is greatly dependent on the
effectiveness of the fuel-injection system. The
injection system has to perform the important
duty of initiating and controlling the
combustion process

10. FUNCTIONAL REQUIREMENTS OF AN
INJECTION SYSTEM
• Accurate metering of the fuel injected per cycle. This is
very critical due to the fact that very small quantities of
fuel being handled.
• Metering errors may cause drastic variation from the
desired output. The quantity of the fuel metered
should vary to meet changing speed and load
requirements of the engine.
• Timing the injection of the fuel correctly in the cycle so
that maximum power is obtained ensuring fuel
economy and clean burning.
• Proper control of rate of injection so that the desired
heat-release pattern is achieved during combustion.

11. FUNCTIONAL REQUIREMENTS OF AN
INJECTION SYSTEM
• Proper atomization of fuel into very fine
droplets.
• Proper spray pattern to ensure rapid mixing of
fuel and air.
• Uniform distribution of fuel droplets in the
combustion chamber.
• To supply equal quantities of metered fuel to all
cylinders in case of multi cylinder engines.
• No lag during beginning and end of injection i.e.,
to eliminate dribbling of fuel droplets into the
cylinder.

12. CLASSIFICATION OF INJECTION
SYSTEMS
The injection systems can be classified as:
(i) Air injection systems
(ii) Solid injection systems

13. Air Injection System
• In this system, fuel is forced into the cylinder by means
of compressed air.
• This system is little used nowadays, because it requires
a bulky multi-stage air compressor.
• This causes an increase in engine weight and reduces
the brake power output further.
• One advantage that is claimed for the air injection
system is good mixing of fuel with the air with resultant
higher mean effective pressure.
• Another is the ability to utilize fuels of high viscosity
which are lessexpensive than those used by the engines
with solid injection systems.
• These advantages are off-set by the requirement of a
multistage compressor thereby making the air-injection
system obsolete.

14. Solid Injection System
• In this system the liquid fuel is injected
directly into the combustion chamber without
the aid of compressed air.
• Hence, it is also called airless mechanical
injection or solid injection system.

15. Classification of Solid Injection System
Solid injection systems can be classified as:
• Individual pump and nozzle system
• Unit injector system
• Common rail system
• Distributor system

16. fuel feed system for a CI engine

17. fuel feed system for a CI engine
All the fuel feed system comprise mainly of the following
components
(i) fuel tank,
(ii) fuel feed pump to supply fuel from the main fuel tank to the
injection system,
(iii) injection pump to meter and pressurize the fuel for injection,
(iv) governor to ensure that the amount of fuel injected is in
accordance with variation in load,
(v) injector to take the fuel from the pump and distribute it in
the combustion chamber by atomizing it into fine droplets,
(vi) fuel filters to prevent dust and abrasive particles from
entering the pump and injectors thereby minimizing the wear
and tear of the components

18. Solid Injection System types

19. distributor system

20. CI Engine Fuels Properties
• Knock Characteristics: Knock in the CI engine
occurs because of an ignition lag in the
combustion of the fuel between the time of
injection and the time of actual burning
• Volatility : The fuel should be sufficiently
volatile in the operating range of temperature
to produce good mixing and combustion
• Starting Characteristics : The fuel should help
in starting the engine easily

21. CI Engine Fuels Properties
• Smoking and Odour : The fuel should not promote
either smoke or odour in the engine exhaust.
• Viscosity : CI engine fuels should be able to flow
through the fuel system and the strainers under the
lowest operating temperatures to which the engine is
subjected to.
• Corrosion and Wear : The fuel should not cause
corrosion and wear of the engine components before
or after combustion
• Handling Ease : The fuel should be a liquid that will
readily flow under all conditions that are encountered
in actual use.