Explanation of CRDI fuel injection and its parts

1. Automotive Electronics-II
Prabin Acharya
1

2. 1.1 Introduction
to Common Rail
Direct Injection
System
(CRDI)
The Common Rail Direct Injection (CRDI)
system is one of the latest innovation for
diesel engines. It stores fuel at high pressure
in a common rail, allowing precise and
efficient fuel delivery to each cylinder. CRDI
enhances combustion efficiency, reducing
emissions, improving fuel economy, and
delivering more power, making it a staple in
modern diesel engines.
2

3. 3

4. Mechanically operated CRDI system
4

5. Electronic CRDI system
5

6. Q) Draw a simple schematic diagram of CRDI system.
Ans: Also add cam, crank speed sensor and accelerator pedal sensor
6

7. Types of Circuit In CRDI
It comprises of two circuits,
1) Low Pressure Circuit
The initial regulation, filtration and pressurization of fuel is done by the
low-pressure circuit. It consists of fuel tank, low pressure pump and fuel
filter.
2) High Pressure Circuit
It ensures the correct injection of the fuel into the combustion
chamber
7

8. 1) Low Pressure Circuit (Fuel Pump Operation)
i) Fuel filter
The fuel is sent to the fuel filter mainly by the fuel pump.
The impurities in the fuel will be cleared through the
paper filter element. The fuel filter of diesel engine filters
out the harmful impurities and moisture in the fuel
system, protect the normal work of the engine, reduce
wear and tear, avoid clogging and improve diesel engine
life. The housing collects the large particle and moisture
in the bottom.
8

9. ii) Fuel Pump (Low pressure
pump)
The fuel injection pump alone
cannot create sufficient vacuum to suck
fuel from fuel tank. Therefore, an auxiliary
pump known as low pressure pump is
used. It sucks the fuel from the fuel tank
and deliver it to the high-pressure pump.
It is a mechanical pump driven by the
high-pressure pump shaft however some
vehicle have an electric low -pressure
pump in addition or instead of low-
pressure mechanical pump.
9

10. Fig: Low pressure pump with vanes and gears.
10

11. iii) Pressure Relief Valve
This component ensures that the fuel
pressure in the low-pressure circuit remains within
the desired range. Excess fuel is returned to the
fuel tank.
11

12. 2) High pressure circuit (High injection pump system)
i) Common Rail (Header)
The pressurized fuel from the high-pressure pump is delivered to a
common rail, a high-pressure accumulator that acts as a reservoir to
store the pressurized fuel. This may be cylindrical or spherical in shape.
The rail has one outlet per cylinder to which injector pipes are
connected.
A rail pressure sensor, pressure relief valve, return lines, etc. are other
components mounted to the common rail.
12

13. ii) Rail Pressure
Sensor
The rail pressure sensor is a
piezo resistive sensor. The
computer uses the rail
sensor signal to control the
pressure regulation system.
Piezoresistive sensors are
pressure sensors that use
the change in electrical
resistance of a material
when stretched to measure
the pressure.
13

14. iii) High pressure pump
• The low-pressure fuel is drawn by the high-pressure pump, which
pressurizes the fuel to a much higher level (up to thousands of psi).
The high-pressure pump is usually driven by the engine's camshaft. It
is generally a reciproacting type pump.
14

15. 15

16. iv) Pressure Relief Valve
A spring-loaded high-pressure relief
valve maintains a constant pressure
in the system and supplies the extra
fuel to the tank. The adjustment
screw is used to vary the pressure
inside the header (common
rail).Nowadays, A solenoid-
controlled valve is used instead of
adjustment screw and spring.
16

17. v) High pressure
injectors
• The fuel injectors are responsible for injecting the pressurized fuel into
the engine cylinders. They open and close rapidly to deliver the fuel in
precise amounts and at the right time. Each cylinder has its own fuel
injector connected to the common rail. The injector is electronically
controlled and opens to release a precise amount of high-pressure fuel
directly into the combustion chamber at the optimal moment.Some of
the injectors uses electromagnet whereas other uses piezo electric
actuators to control the supply of the fuel .
17

18. vi) Return Lines
It is a fuel line that carries excess fuel back to the fuel tank. The fuel return line
is an integral part of the common rail system as it ensures that the fuel
pressure remains within the desired range. It also helps in preventing the fuel
from overheating and foaming, which could negatively impact the
performance of the injection system.
18

19. Assignment for Chapter 1
Q1) Explain construction and working of electronic unit injector with
a sketch. (6)
Q2) Draw the sketch of electronic Common Rail Diesel Injection (CRDI)
system and label the parts. (6)
Q3) Sketch and explain the fuel filter (3).
19