HOMOGENEOUS CHARGE COMPRESSION IGNITION

Why HCCI Engine ?

 High efficiency and ultra low emission with respect to
conventional Diesel engine.
 To achieve near zero NOx and soot emission
 To achieve latest Euro Norms ( E5)
 To reduce fuel consumption, greenhouse gas emission.

Law of Diesel HCCI –

Every one percent increase of diesel HCCI car saves 90 million liters of
fuel per year. This corresponds to emission saving of some 210000
metric tones of CO2

What Is HCCI?
 HCCI is a combustion process. HCCI is not an engine concept. HCCI
must be incorporated in an engine concept.
 HCCI is a low temperature chemically controlled (flameless)
combustion process.
 HCCI can be considered as a hybrid form between the diesel and
Otto combustion process.
 However combustion process is different. So there is neither
Diffusion flame (as in a diesel engine) nor a flame front traveling
through a premixed charge ( as in SI engine).
WORKING PRINCIPLE OF HCCI:
 Homogenous charge is drawn in to the cylinder during suction
and compress to high enough temperature to achieve
spontaneous ignition of the charge.
 Combustion starts in almost whole volume of C.C Two degree
before TDC
 After Combustion initiation the temperature rapidly increases and
whole fuel burn simultaneously As whole mixture burns
simultaneously and no flame propagation , combustion
temperature can be controlled less than 700 deg Centigrade and
thus NOx formation is avoided.
HCCI Drawbacks:
 Higher load HCCI operation is difficult.
 To achieve Transient operation and cold starting are issues.
 Start of combustion (SOC) is difficult to control because there is
no direct ignition source such as a spark plug or fuel injection
 timing. Instead SOC is controlled by mixture properties at intake
valve closing.
 Controlling how rapidly the energy is released is also a problem.
For this reason significant EGR dilution is needed.
 CO and UHC emissions are also high at light loads

HCCI Benefits:
 Ultra-low NOx emissions because there is no propagating flame
front and the burning is both locally and globally lean.
 Extremely low PM emissions because the mixture is homogeneous
and there are no rich pockets
 Significant part load efficiency gains over SI because the engine is
operated unthrottled and load is controlled by fuelling and
varying the fuel to air ratio.
 Homogeneous Charge Compression Ignition (HCCI) engines have
the potential of producing a high thermal efficiency with
extremely low PM and NOx emissions.
 AIR ASSISTED COMBUSTION

 The injection system required pressurised supplies of both fuel

and air.
 The air pressure was supplied from a cylinder of compressed air,
using a regulator on the cylinder to set and control the supply
pressure.
 The return from the injector was then connected to the regulator
block.
 The system uses a conventional multipoint injector to meter fuel
into a chamber.
 This dramatically improves fuel atomisation, allowing the use of a
very low injection pressure which in turn reduces the spray
velocity and penetration of the fuel into the cylinder.
 The supply pressure from the bottle was set just higher than the
regulators' rated pressure so a small amount of air was
continuously dumped to atmosphere.
 However, care had to be taken to ensure that the supply pressure
from the bottle was set correctly. If the supply pressure was set
too high then the regulator may not have been able to dump
sufficient air and the pressure at the injector would be too high.
 Instead, the supply pressure was set by monitoring the supply
pressure to ensure that the regulator was always functioning
within its operating range.
 The fuel pressure was set at 1.5 bar higher than the air pressure, a
supply pressure of over 8 bar was required. After leaving the
pumps, the fuel passed to the injector via a filter.
 As with the air supply, the return from the injector was connected
to the regulator block. However, unlike the air supply that takes it
reference pressure from the atmosphere, the fuel regulator takes
its reference pressure from the air supply pressure.
 In this way the fuel pressure is always controlled relative to the
air pressure.
 The main reason for doing this is to ensure that the pressure
across the fuel injector is always constant, thereby allowing it to
be accurately calibrated.
 If for any reason the air pressure varies slightly the calibration
will be preserved.
 Advantages

 Because of excellent atomization and better distribution of fuel,

combustion will be more efficient and complete. This will result in
a relatively higher mean effective pressure.
 Due to good atomization and distribution of fuel, effective
utilization of air charge is possible. This implies reduced excess
air requirement.
 With reduced air charge, combustion chamber as well as cylinder
size become smaller for the given power output.

Disadvantage

 An injection requires a high pressure air compressor. This is

relatively heavy. This also absorbs part if the engine power. Hence
the mechanical efficiency goes down
 The high pressure air injection with fuel cools the cylinder charge,
due to the turbulence created by it. Compact cylinder size reduces
heat losses. The former effect predominates over the latter effect.
As such a fairly high compression ratio is required.
 NOx ADSORBERS

Lean engines enable better fuel efficiency and lower operating

costs; however, NOx emissions from lean engines are difficult to control.
Three-way catalysts commonly applied to stoichiometric engines for
NOx control do not reduce NOx in lean exhaust due to the excess oxygen
in the exhaust. Selective catalytic reduction with ammonia or urea based
solutions is capable of reducing NOx in lean exhaust; however, the
requirements for ammonia or urea storage are often undesirable or
impractical for many applications. Lean NOx trap (also known as NOx
adsorber) catalysts have been effectively reduced NOx emission on lean
burn diesel and gasoline reciprocating engines and on natural gas-fired
turbines.

Working principle:
Lean NOx trap catalysts operate in a cyclic fashion. During lean
operation, the catalyst adsorbs ("traps") NOx in the exhaust onto
storage sites on the catalyst. The process is called "sorption" and can
occur at >90% trapping efficiencies.
The catalyst is composed of alkali or alkaline earth materials (Pt)
that form nitrate species on the surface of the catalyst during the
sorption phase. Once these nitrate species begin to saturate the catalyst,
NOx trapping efficiencies begin to deteriorate, and the catalyst must be
"regenerated" to renew the active sorption sites for more NOx storage.
“Regeneration” occurs during net-reducing (rich) conditions and allows
release of the nitrate species from the alkali/alkaline earth sites and
reduction of the NOx into nitrogen.
After regeneration, the alkali/alkaline earth materials are again
active for NOx trapping, and the lean rich cyclic process begins again.
The regeneration process can occur relatively rapidly in comparison to
the NOx saturation periods observed during sorption. In order to
perform regeneration of the catalyst in applications where lean
operation is the norm, excess fuel is introduced into the system and
combusted to achieve the rich conditions. This excess fuel represents a
fuel penalty.
In engine the fuel was injected into the exhaust system
periodically and combusted over a methane oxidation catalyst to enable
regeneration. As described below, a valved exhaust system was
employed to control exhaust oxygen mass flow which reduced fuel
requirements for the regeneration process.
 Two injectors were mounted on the inlet cone to the catalyst
chamber so that fuel could be injected into the catalyst chamber during
regeneration; the solenoid injectors were operated with a signal to
control flow rate. The fuel supply for the injectors was the same supply
for the engine, and the fuel line to the injectors was located downstream
of the fuel meter. The injector fueling rate is controlled by via data
acquisition.

Advantages
 Lean NOx trap catalysts have greater than 90% NOx reduction in
lean exhaust from engine.
 Same fuel act as a reducing agent which, eliminating the
requirement for storage and handling of secondary fuels.
 Easy to control the trap by combined with data acquisition
system.
  Higher NOx storage capacity indicates less catalyst volume and
lower cost is required for a given engine emission rating and
exhaust temperature.

ONBOARD DIAGNOSTICS

On-board diagnostic systems (OBD) were developed in the 1980's

to help technicians diagnose and service the computerized engine
systems of modern vehicles. OBD monitors the components that make
up the emission system and key engine components. It can usually
detect a malfunction or deterioration of these components before the
driver becomes aware of the problem. When a problem that could cause
a substantial increase in air emissions is detected, the OBD system turns
on a dashboard warning light to alert the driver of the need to have the
vehicle checked by a repair technician. Early OBD systems included a
Malfunction Indicator Light (MIL). This used a rudimentary blinking
light system where the number of blinks could be counted.
This blink count could be cross-referenced against a list to find
the problem indicated. Over the years, there have been many
refinements and improvements. A new generation of these systems
called OBD II is present on 1996 and newer vehicles. The latest OBDII
standard is far more complex and includes a data link connector for
connection of an OBDII scan tool which can be a dedicated hand-held
unit.
Alternatively, it may connect to a laptop computer via a cable that
includes some form of signal processing and which is used in
conjunction with special software. Either approach can be used to
retrieve information from the vehicle.

There are two types of monitors:

Continuous:
These monitors run all the time as long as the key is turned on
and/or the engine is running. There are three continuous monitors that
every OBDII equipped vehicle has, they are the Comprehensive
Component Monitor, The Fuel Monitor and the Misfire Monitor.

Non-Continuous:
These monitors require certain conditions such as speed,
acceleration/deceleration, fuel level, ambient and other conditions to be
met in order for the monitor to run its testing sequence. If the specific
conditions are not met, then the monitor will not perform its tests and
cannot report as to whether or not there are any problems.
Noncontinuous monitors include the Catalyst, Heated Catalyst,
Evaporative System, Secondary Air System, Air Conditioning (A/C)
System, Oxygen (O2) Sensor, Heated O2 Sensor and Exhaust Gas
Recirculation (EGR) System.

Working principle
A basic OBD system consists of an ECU (Electronic Control Unit),
which uses input from various sensors (e.g., oxygen sensors) to control
the actuators (e.g., fuel injectors) to get the desired performance. The
"Check Engine" light, also known as the MIL (Malfunction Indicator
Light), provides an early warning of malfunctions to the vehicle owner.
A modern vehicle can support hundreds of parameters, which can be
accessed via the DLC (Diagnostic Link Connector) using a device called a
scan tool. OBD II standardizes that many trouble codes which are set
when a malfunction is detected in the emission related component of
that the vehicle will be stored in computer memory. OBD II mandates
that all trouble codes are logged when they are set and are retrieved by
the scan tool when commanded. OBD II however turns on the
Malfunction Indictor Light (MIL) selectively in malfunction situations
that require immediate attention of the driver for safety reasons.
The comprehensive components are mostly inputs and outputs to
the power train which are sensors, and the actuators. OBD II has to
communicate the diagnostic information to the vehicle mechanic via a
communication network using diagnostic trouble codes (DTCs). The
DTCs are defined by four basic categories. General Circuit Malfunction,
Malfunction Range/ Performance Problem, Low and High Circuit input.
The DTC consists of an alpha numeric icon. Each defined fault code is
assigned a message to indicate the circuit, component, or system area
that was diagnosed as faulty. The messages are organized such that
different messages related to a particular different sensor or systems
are grouped together. Each group has a generic code as the first Code/
Message that indicates the generic nature of the fault. The manufacturer
has a choice to define more specific DTC for each lower level fault in that
group. However, only one Code must be stored in OBD II for each fault
detected circuit. Comprehensive Components Monitoring includes all
the sensors, solenoids, fuel injectors, fuel pump, ignition coil, actuators
(valves), and the associated wiring, ground, and power supply.
 The OBD II diagnostics consist of conducting tests on all the
sensors and actuators listed above. If any fault is detected in any of the
tests of these devices including , sensor or actuator component,
electrical circuit, wiring, and power source, the corresponding
diagnostic trouble code (DTC) assigned in that fault, is displayed and the
malfunction indication light (MIL)is illuminated.
 Variable-geometry turbocharger

 Variable-geometry or variable-nozzle turbo chargers use

moveable vanes to adjust the airflow to the turbine, imitating a
turbocharger of the optimal size throughout the power curve
 The vanes are placed just in front of the turbine like a set of
slightly overlapping walls. Their angle is adjusted by an actuator
to block or increase air flow to the turbine.
 This variability maintains a comparable exhaust velocity and back
pressure throughout the engine's speed range.
 For a slow speed the angle between the vanes are too small, which
makes increasing gas velocity to run the turbine
 At higher speed the angle between the vanes are high for
increasing the turbine capacity to produce maximum power.
 The result is that the turbocharger improves fuel efficiency
without a noticeable level of turbocharger lag.
HYBRID ELECTRIC VEHICLE:
 HEV often simply referred to as hybrid vehicles, are powered by a
combination of electricity stored in a battery and either a petrol
or diesel internal combustion engine. A hybrid vehicle does not
need to be plugged in to recharge its battery, as this is recharged
automatically as the vehicle is being driven. A hybrid electric
vehicle (HEV) has two types of energy storage units, electricity
and fuel. Electricity means that a battery (sometimes assisted by
ultracaps) is used to store the energy, and that an electromotor
(from now on called motor) will be used as traction motor.

Types by drive train structure

a) Series hybrid
In a series hybrid system, the combustion engine drives an
electric generator (usually a three-phase alternator plus rectifier)
instead of directly driving the wheels.

The electric motor is the only means of providing power to the

wheels. The generator both charges a battery and powers an electric
motor that moves the vehicle. When large amounts of power are
required, the motor draws electricity from both the batteries and the
generator Series hybrid configurations already exist a long time: diesel-
electric locomotives, hydraulic earth moving machines, diesel-electric
power groups, loaders.
Series hybrids can be assisted by ultracaps (or a flywheel:
KERS=Kinetic Energy Recuperation System), which can improve the
efficiency by minimizing the losses in the battery. They deliver peak
energy during acceleration and take regenerative energy during
braking. Therefore, the ultracaps are kept charged at low speed and
almost empty at top speed. Deep cycling of the battery is reduced; the
stress factor of the battery is lowered. A complex transmission between
motor and wheelis not needed, as electric motors are efficient over a
wide speed range. If the motors are attached to the vehicle body, flexible
couplings are required.
Some vehicle designs have separate electric motors for each
wheel. Motor integration into the wheels has thedisadvantage that the
unsprung mass increases,decreasing ride performance. Advantages of
individual wheel motors include simplified traction control (no
conventional mechanical transmission elements such as gearbox,
transmission shafts, differential), all wheel drive, and allowing lower
floors, which is useful for buses. Some 8x8 all-wheel drive military
vehicles use individual wheel motors.

Advantages of series hybrid vehicles:

 There is no mechanical link between the combustion engine and
the wheels. The engine generator group can be located
everywhere.
 There are no conventional mechanical transmission elements
(gearbox, transmission
 shafts). Separate electric wheel motors can be implemented
easily.
 The combustion engine can operate in a narrow rpm range (its
most efficient range), even as the car changes speed.
 Series hybrids are relatively the most efficient during stop-and-go
city driving.

Weaknesses of series hybrid vehicles:

 The ICE, the generator and the electric motor are dimensioned to
handle the full power of the vehicle. Therefore, the total weight,
cost and size of the powertrain can be excessive.
 The power from the combustion engine has to run through both
the generator and electric motor. During long-distance highway
driving, the total efficiency is inferior to a conventional
transmission, due to the several energy conversions.

b) Parallel hybrid:
 Parallel hybrid systems have both an internal combustion engine
(ICE) and an electric motor in parallel connected to a mechanical
transmission. Most designs combine a large electrical generator and a
motor into one unit, often located between the combustion engine and
the transmission, replacing both the conventional starter motor and the
alternator (see figures below). The battery can be recharged during
regenerative breaking, and during cruising (when the ICE power is
higher than the required power for propulsion). As there is a fixed
mechanical link between the wheels and the motor (no clutch), the
battery cannot be charged when the car isn’t moving.

the vehicle is using electrical traction power only, or during brake

while regenerating energy, the ICE is not running (it is disconnected by
a clutch) or is not powered (it rotates in an idling manner).

Advantages of parallel hybrid vehicles:

 Total efficiency is higher during cruising and long-distance
highway driving.
 Large flexibility to switch between electric and ICE power.
 Compared to series hybrids, the electromotor can be
designed less powerful than the ICE, as it is assisting
traction. Only one electrical motor/ generator is required.
Weaknesses of parallel hybrid vehicles:
 Rather complicated system.
 The ICE doesn't operate in a narrow or constant RPM range, thus
efficiency drops at low rotation speed.
 As the ICE is not decoupled from the wheels, the battery cannot be
charged at standstill.
c) Combined hybrid:
 Combined hybrid systems have features of both series and
parallel hybrids. There is a double connection between the engine and
the drive axle: mechanical and electrical.
This split power path allows interconnecting mechanical and
electrical power, at some cost in complexity. Power-split devices are
incorporated in the powertrain.
The power to the wheels can be either mechanical or electrical or
both. This is also the case in parallel hybrids. But the main principle
behind the combined system is the decoupling of the power supplied by
the engine from the power demanded by the driver.

In a conventional vehicle, a larger engine is used to provide

acceleration from standstill than one needed forsteady speed cruising.
This is because a combustion engine's torque is minimal at lower RPMs,
as the engine is its own air pump.
On the other hand, an electric motor exhibits maximum torque at
stall and is well suited to complement the engine's torque deficiency at
low RPMs. In a combined hybrid, a smaller, less flexible, and highly
efficient engine can be used. It is often a variation of the conventional
Otto cycle, such as the Miller or Atkinson cycle. This contributes
significantly to the higher overall efficiency of the vehicle, with
regenerative braking playing a much smaller role.
At lower speeds, this system operates as a series HEV, while at
high speeds, where the series power train is less efficient, the engine
takes over. This system is more expensive than a pure parallel system as
it needs an extra generator, a mechanical split power system and more
computing power to control the dual system.

Advantages of combined hybrid vehicles:

  Maximum flexibility to switch between electric and ICE power.
 Decoupling of the power supplied by the engine from the power
demanded by the driver allows for a smaller, lighter, and more
efficient ICE design.

Weaknesses of combined hybrid vehicles:

 Very complicated system, more expensive than parallel hybrid.
 The efficiency of the power train transmission is dependent on
the amount of power being transmitted over the electrical path, as
multiple conversions, each with their own efficiency, lead to a
lower efficiency of that path (~70%) compared with the purely
mechanical path (98%).

COMMON RAIL DIRECT INJECTION DIESEL ENGINE

Common rail direct fuel injection is a modern variant of direct fuel
injection system for petrol and diesel engines. Common rail is a
modular, Electronically Controlled Diesel Fuel Injection System. The
particular design of common rail, with its flexible division of injection
into several injections (pre, main and post injections), allows the engine
and the injection system to be matched to each other in the best
possible way.
The common rail technology makes available provides better fuel
atomization. To lower engine noise, the engine's electronic control unit
can inject a small amount of diesel just before the main injection event
("pilot" injection), thus reducing its explosiveness and vibration, as well
as optimizing injection timing and quantity for variations in fuel quality,
cold starting and so on.

At the heart of the Common Rail System, are the following

components:

 High Pressure Pump, for generating pressure in the rail.

 Rail, which contains the pressurized reserves of fuel.
 Injectors, which inject the requisite precise quantities of fuel into
the combustion chamber.
 Electronic Control Unit (ECU), which acts as the control centre
with inputs from a number of sensors.
Working principle:
 In the Common Rail System, the injection are performed
separately - by first generating and storing the fuel under high
pressure in a central rail, then delivering it to the individual
cylinders through the electronically-controlled injectors on
demand.
 Fuel is passed through filter then enters into the feed pump,
which transfer the fuel in to the fuel pump with moderate
pressure.
 A high-pressure pump generates in an accumulator - the rail - a
pressure of up to 1,600 bar (determined by the injection pressure
setting in the engine control unit), independently of the engine
speed and the quantity of fuel injected.
 When the fuel injectors are electrically activated, a hydraulic valve
(consisting of a nozzle and plunger) is mechanically or
hydraulically opened and fuel is sprayed into the cylinders at the
desired pressure.
 The pressure regulator is used to adjust the common rail
pressure, which is controlled by ECU signal.
  This ensures that incredibly high injection pressures are available
at all times, even at low engine speeds.
 The ECU controls all the injection parameters with extreme
precision - such as the timing and injection quantity, as well as
performing other engine functions.

Advantages
 The compact design of the injector outline enables the common
rail system to be used on two or four valve per cylinder engines.
 With one electronically driven injector per engine cylinder, the
system is modular and can be used on three-, four-, five-, and six-
cylinder engines.
 This allows the engine to develop high torque at low revs and
across a wide power range. The result is an engine which is
smooth, responsive and which offers excellent pick-up for safe
and easy overtaking.
 In addition, fuel economy is maintained even at all loading
conditions.
 The injection pressure is independent of the engine speed and
load, enabling high injection pressures at low speed if required.
 Injection sequences, which include periods both pre and post the
main injection, can be utilized to reduce emissions, particularly
NOx,
 Common rail offers all the benefits of full electronic control fuel
metering and timing, as well as the option to interface with other
vehicle functions.