2. Introduction
The task of the engine induction and fuel systems is to
prepare an air-fuel mixture that satisfies the requirement of
the engine.
This preparation is to be carried out over entire engine
operating system.
In principle, the optimum air-fuel ratio for an engine is that
which give the required power output with the lowest fuel
consumption.
It should also ensure smooth and reliable operation.
The fuel Induction systems for SI engine are classified as:
Carburetors.
Throttle body Fuel Injection Systems.
Multi Point Fuel Injection Systems.
4. Requirements of Good Fuels
Viscosity
Low & Constant over wide range of temp
Pour point
Higher than operating conditions
Sulphur Contain
No
Volatility
Moderate so to mix with air
Heat of Combustion
High
Product of Combustion
No or Very Less
Cost
Low
5. Air –Fuel Ratio
The air-fuel ratio is the proportions of air and gasoline mixed by
the carburettor as required for combustion by the engine.
This ratio is extremely important for an engine because there are
limits to how rich (with more fuel) or how lean (with less fuel) it
can be, and still remain fully combustible for efficient firing.
Engine can operate range from 8:1 to 18.5:1
6. Stoichiometric Ratio 14.7:1
The best fuel economy at 15:1 to 16:1
maximum power output at 12.5:1 to 13.5:1
A:F Power Economy Co/HC Nox
Lean Low High Low High
Rich High Low High Low
7. Mixture Requirements of
Engine
Operating conditions:
Idling
Cursing
High Power
Operation Governing Factor Mix Requirement
Idling Dilution of Mixture Rich
Cursing / Normal Economy Slight Lean
High Power/ Acceleration Full Air Utilization Rich
Cold Starting & Warmup Engine Temperature Rich
Accelerating Liquid film / non-
vaporized droplet
Rich
8. Carburetor & Carburetion
Carburetor is device that atomizes and vaporizes the
fuel and mixes with air in varying proportion to suit SI
engine operating range.
Carburetion is process of braking up and mixing the
fuel with air .
Factors affecting carburetion
Engine Speed
Vaporization Characteristic of Fuel
Temperature of Incoming Air
Design of Carburetor
10. Types of Simple Carburetor
Downdraft Up-Draft Horizontal
Draft
11. Requirements of Good
Carburetor
Easy Starting or Cold Starting
Must atomize fuel and air mix homogeneously
Provide correct air fuel ratio
Must run engine smoothly without wastage of fuel
Must provide rich mixture during idling and starting and
sudden acceleration
It should function correct during changing climatic
condition
12. Limitations of Simple Carburetor
(Single Jet Carburetor)
Can’t provide Rich Mixture during Starting or No / low
Load
Can’t provide Rich Mixture during sudden acceleration
Cold starting problem
Can’t provide correct A:F during operating conditions
like Idling, Normal Running and Accelerating.
Can’t adjust mixture quantity for Change in altitude
13. Complete Carburetor
Main metering system :
(To supply correct A:F ratio during required operating conditions)
Idling system
Power enrichment system
Acceleration system
Choke
14. Main Metering System
Compensating Jet Device
Emulsion tube or Air Bleeding System
Back Suction Control or Pressure Reduction
Auxiliary Valve and Auxiliary Port