ArulmiguMeenakshi Amman College of Engineering
Vadamavandal-604410.
Important questions and answers
CME394- ADVANCED INTERNAL COMBUSTION ENGINEERING
Prepared by
V.Umapathy,
Prof. /Mech.
S.No. Questions and answers
Unit-I
SPARK IGNITION ENGINES
2 – marks question and answers
1. Where are spark ignition engines used?
Two-stroke SI Engines are used in small vehicles like mopeds and scooters. These engines are used for
lawnmowers. These are used in small electricity-generating sets and pumping sets. Four-stroke SI engines
are largely used in automobile industries.
2. What are the mixture requirements for spark ignition engine?
The best fuel economy is obtained with a 15:1 to 16:1 ratio, while maximum power output is achieved with
a 12.5:1 to 13.5:1 ratio. A rich mixture in the order of 10:1 is required for idle heavy load, and high-speed
conditions. SI engine produces less noise and vibration and their starting is very easy.
3. What is the fuel system of spark ignition engine?
The fuel flows from fuel tank to the carburetor under the action of gravity. There are one or two filters
between fuel tank and carburetor. A transparent sediment bowl is also provided to hold the dust and dirt of
the fuel.
,4. What is single point fuel injection system?
Single-point injection (also called 'throttle-body injection') uses one injector in a throttle body mounted
similarly to a carburetor on an intake manifold.
5. What is the multipoint fuel injection system?
What is MPFI system? Multi-Point Fuel Injection (MPFI) refers to a method of injecting fuel through
multiple ports on each cylinder's intake valve. This precision enhances combustion efficiency, improving
engine performance and fuel economy.
6. What is the main advantage of a multi-point injection system?
Multi-point fuel injection boasts the advantage of reduced friction losses in partial-load operation, while
direct fuel injection has a higher knocking limit when close to full load.
7. What is direct fuel injection system?
Direct fuel injection systems can optimize fuel delivery by injecting fuel directly into the cylinder at a high
pressure, in contrast to conventional systems that inject fuel into the intake air stream at a lower pressure.
8. What are the stages of the combustion engine?
(iv) After Burning Page 9 • Combustion in CI Engines • Thus, it is seen that the complete combustion in CI
engines may be comprising of four distinct phases i.e. 'ignition delay' followed by 'uncontrolled
combustion,' 'controlled combustion' and 'after burning'.
9. What is the difference between normal and abnormal combustion?
Normal combustion is the process where the fuel is burned layer by layer i.e. in a wave form by the help of
spark only. And abnormal combustion is the process where the fuel burns not only by spark but also by self
, ignition process where a no. of waves of flames is produced from different parts of cylinder.
10. What is the knocking phenomenon in spark ignition engines occur due to?
The knocking combustion is related to local auto-ignition and pressure wave reflection near the walls. It
was found that the 1st auto-ignition spot occurs ahead of the flame front because the end-gas mixture
closer to the flame front has higher temperatures.
13 and 15 marks question and answers
11.
With neat diagram explain Mono-point Fuel injection systems.
Mono-point Fuel injection systems
A "mono-point" fuel injection system, also called "single-point injection" or "throttle body injection
(TBI)", refers to a fuel injection system where only one fuel injector is used, located within the throttle
, body of a spark ignition engine, delivering fuel to all cylinders by mixing it with air before it enters the
intake manifold, essentially acting as a more precise alternative to a carburetor; this system is considered
outdated due to its less precise fuel distribution compared to newer multi-point injection systems.
Key points about mono-point fuel injection:
Single injector:
Unlike multi-point injection, where each cylinder has its own injector, a mono-point system uses just one
injector placed in the throttle body.
Mixing in the throttle body:
The fuel is sprayed directly into the air stream as it enters the throttle body, where it mixes with the air
before being distributed to all cylinders through the intake manifold.
Simpler design:
This system was initially popular as it required minimal changes to existing engine designs, particularly
when replacing carburetors, making it a cost-effective option.
Disadvantages:
Uneven fuel distribution: Due to the single injector, there can be uneven fuel distribution
among cylinders, leading to potential performance issues.
Less efficient: Compared to multi-point injection, the mono-point system may not deliver as
precise fuel control, impacting fuel efficiency.
How it works:
1. Fuel pump:
The fuel pump pressurizes the fuel from the fuel tank.
2. ECU signal:
The engine control unit (ECU) sends a signal to the fuel injector based on engine conditions like throttle
Vadamavandal-604410.
Important questions and answers
CME394- ADVANCED INTERNAL COMBUSTION ENGINEERING
Prepared by
V.Umapathy,
Prof. /Mech.
S.No. Questions and answers
Unit-I
SPARK IGNITION ENGINES
2 – marks question and answers
1. Where are spark ignition engines used?
Two-stroke SI Engines are used in small vehicles like mopeds and scooters. These engines are used for
lawnmowers. These are used in small electricity-generating sets and pumping sets. Four-stroke SI engines
are largely used in automobile industries.
2. What are the mixture requirements for spark ignition engine?
The best fuel economy is obtained with a 15:1 to 16:1 ratio, while maximum power output is achieved with
a 12.5:1 to 13.5:1 ratio. A rich mixture in the order of 10:1 is required for idle heavy load, and high-speed
conditions. SI engine produces less noise and vibration and their starting is very easy.
3. What is the fuel system of spark ignition engine?
The fuel flows from fuel tank to the carburetor under the action of gravity. There are one or two filters
between fuel tank and carburetor. A transparent sediment bowl is also provided to hold the dust and dirt of
the fuel.
,4. What is single point fuel injection system?
Single-point injection (also called 'throttle-body injection') uses one injector in a throttle body mounted
similarly to a carburetor on an intake manifold.
5. What is the multipoint fuel injection system?
What is MPFI system? Multi-Point Fuel Injection (MPFI) refers to a method of injecting fuel through
multiple ports on each cylinder's intake valve. This precision enhances combustion efficiency, improving
engine performance and fuel economy.
6. What is the main advantage of a multi-point injection system?
Multi-point fuel injection boasts the advantage of reduced friction losses in partial-load operation, while
direct fuel injection has a higher knocking limit when close to full load.
7. What is direct fuel injection system?
Direct fuel injection systems can optimize fuel delivery by injecting fuel directly into the cylinder at a high
pressure, in contrast to conventional systems that inject fuel into the intake air stream at a lower pressure.
8. What are the stages of the combustion engine?
(iv) After Burning Page 9 • Combustion in CI Engines • Thus, it is seen that the complete combustion in CI
engines may be comprising of four distinct phases i.e. 'ignition delay' followed by 'uncontrolled
combustion,' 'controlled combustion' and 'after burning'.
9. What is the difference between normal and abnormal combustion?
Normal combustion is the process where the fuel is burned layer by layer i.e. in a wave form by the help of
spark only. And abnormal combustion is the process where the fuel burns not only by spark but also by self
, ignition process where a no. of waves of flames is produced from different parts of cylinder.
10. What is the knocking phenomenon in spark ignition engines occur due to?
The knocking combustion is related to local auto-ignition and pressure wave reflection near the walls. It
was found that the 1st auto-ignition spot occurs ahead of the flame front because the end-gas mixture
closer to the flame front has higher temperatures.
13 and 15 marks question and answers
11.
With neat diagram explain Mono-point Fuel injection systems.
Mono-point Fuel injection systems
A "mono-point" fuel injection system, also called "single-point injection" or "throttle body injection
(TBI)", refers to a fuel injection system where only one fuel injector is used, located within the throttle
, body of a spark ignition engine, delivering fuel to all cylinders by mixing it with air before it enters the
intake manifold, essentially acting as a more precise alternative to a carburetor; this system is considered
outdated due to its less precise fuel distribution compared to newer multi-point injection systems.
Key points about mono-point fuel injection:
Single injector:
Unlike multi-point injection, where each cylinder has its own injector, a mono-point system uses just one
injector placed in the throttle body.
Mixing in the throttle body:
The fuel is sprayed directly into the air stream as it enters the throttle body, where it mixes with the air
before being distributed to all cylinders through the intake manifold.
Simpler design:
This system was initially popular as it required minimal changes to existing engine designs, particularly
when replacing carburetors, making it a cost-effective option.
Disadvantages:
Uneven fuel distribution: Due to the single injector, there can be uneven fuel distribution
among cylinders, leading to potential performance issues.
Less efficient: Compared to multi-point injection, the mono-point system may not deliver as
precise fuel control, impacting fuel efficiency.
How it works:
1. Fuel pump:
The fuel pump pressurizes the fuel from the fuel tank.
2. ECU signal:
The engine control unit (ECU) sends a signal to the fuel injector based on engine conditions like throttle
