ABSTRACT
Are two stroke motorbikes
poised for a comeback? With new development, they can compete with four stroke
in emission cleanliness, full economy & rideability while retaining power,
size & weight advantages.
Now days this is the age of
four-stroke engme. Because of its various advantageous like mileage, power and
one of the greatest advantage is that it's emission.
And therefore it is certify that it is cleanliness
and made very low pollution. Because of this the two stroke engine is left out
from the market. All the giant companies turn towards four stroke engines.
At this stage were there is
no demand for two stroke engine, because of the concentrated effort of an
Australian base Orbital Engine Company take a giant leap, they took back two
stroke engine technology, having advantageous over four stroke engine in all
respect. And which is tie with greatest automobile companies like Peugot ,
Aprila and Bajaj also. This technology not restricted only for two-wheeler but
also use in four-wheeler like BMW& Ford also.
INTRODUCTION
When two-stroke motorbikes
comes to off road motor cross racing.
Two stroke-powered bikes have always taken the lead.
But its harmful emission forced the Environmental Protection Agency to ban them
from rallies in America.
Finally after a long wait two stroke returning to the circuit with a total
redesign of engine, its fuel injection system, & working. This was possible
due to the concentrated effort of an Australian organization, the Orbital
Engine Company that pioneered the development of direct in cylinder fuel
injection system, which reduces emission level but also increases power. In
addition the redesign of the combustion chamber & valve mechanism by Honda
& Bimota has enabled them to run the engine without spark plugs! In basic
two stroke working cycle, fuel enter the cylinder through the intake port from
one side of the cylinder & pushes spent exhaust gases out of the exhaust
port on the opposite cylinder wall at the same time. This causes the fuel to
mix with the exhaust gases. Some amount of exhaust gas invariably remains in
the cylinder as the fresh charge comes in. When spark plug ignites the fuel
mixture, some fuel is isolated from the flame by the exhaust gases still in the
cylinder Goes not bum.
Thus two basic disadvantages arise:
incomplete combustion of fuel at low engine rpm, & expulsion at high engine
rpm. Moreover the oil injected into the motor to lubricate the crankshaft is
also bum off the combustion. This result more pollution than permissible
limits. Some new technologies have been making waves in low emission high
performance 2-stroke engine. The three different innovations competing for the
right to save future Two-stroke are direct fuel injection, exhaust trapping
valves & active radial combustion.
CONVENTIONAL
TWO-STROKE ENGINE
The air or charge is sucked
through spring loaded inlet valve when the pressure in the crankcase reduces
due to upward motion of the piston during compression stroke. After the
compression stroke, ignition & expansion takes place in the usual way.
During the expansion stroke the air in the crankcase is compressed. Near the
end of expansion stroke piston uncover the exhaust port
And the cylinder pressure
drops to atmospheric as the combustion products leave the cylinder. Further
motion of the piston uncovers the transfer port, permitting the slightly
compressed air or mixture in the crankcase to enter engine cylinder. This
causes the fuel to mix with the exhaust gases. Some amount of exhaust gas
invariably remains in the cylinder as the fresh charge comes in. When spark
plug ignites the fuel mixture, some fuel is isolated from the flame by the
exhaust gases still in the cylinder & does not bum. For this some provision
is done, the top of Next Generation
2-Stroke Engine the piston usually has a projection to deflect the fresh air to
sweep up to top of the cylinder before flowing to the exhaust port. This serves
the double purpose of scavenging the upper part of the cylinder of combustion
product & preventing the fresh charge from flowing directly to the exhaust
ports. The same objective can be achieved without piston deflector by proper
shaping of the transfer port. During the upward motion of the piston from BDC,
the transfer ports &then the exhaust port close & compression of the
charge begins &cycle is repeated.
3.1 SCAVENGING PROCESS: -
At the end of expansion
stroke, the combustion chamber of the two stroke engine is left full of
products of combustion. This is because, there is no exhaust stroke is
available to clear the cylinder of burnt gases. The process of clearing the
cylinder after the expansion stroke is called scavengmg.
4. AIR ASSISTED DIRECT INJECTION SYSTEM (ASDI)
Developed by Orbital leading
international developer of engine technologies direct in cylinder fuel
injection & lean bum system for enhanced fuel economy & lower emission.
This technology exceeds the EP A 2006 emission standards & offers 40% fuel
efficiency over conventional two stroke. Different automotive companies have
licensed & experimented with Orbital clean burning two-stroke engine &
auto major like Peugot, Aprila & other are directly installing these on
their new models. It may not take long before this technology reaches India as Bajaj
auto already has a tie-up with Orbital. This technology is not only restricted
to two wheeler but Ford, BMW and other four wheeler auto majors have used this
technology to manufacture cars powered with ASDI
Two stroke engine which much better performance than
an equivalent four stroke engine
4.1 PRINCIPAL OF ASDI: -
Compressed air is used to
assist the atomization of fuel injected directly into the combustion chamber,
(typically after the exhaust port has closed) facilitating very fine control of
air-fuel gradient around the spark plug. In addition, the air utilizes to
scavenge and clean out the cylinder of bum gases. The Honda EXP-2& Bimota 500V
uses the same technology. But it was Orbital modified Honda NSR- 125 that
sparked this new trend. A new injection system and a compressor to supply the
air for injection were the only equipment fitted. All the other parts were left
in tact.
One of the central
components of the Orbital combustion process is the direct injector. This
injector can deliver extremely small droplets & control spray geometry
directly in cylinder. The compressor pumps in 5.5 bar of air to affect the
injection and atomization fuel at pressure, normal fuel pump can use. A
detailed schematic diagram of fuel injection system is shown in fig 2.
The
fuel is injected into the cylinder by a compressed air assisted direct
injector. After the fuel catches the fire and power stroke is performed, the
exhaust gases are scavenged out using air only & sensor fitted make sure
that no unbunrt fuel is driven out. The fuel injection and scavenging is
controlled by an Electronic Control Unit (ECU) in response ·to engine speed and
rider demand. With the modified NSR-125 performing at par & consuming less
fuel. Orbital demonstrated that fuel system alone; independent of any
optimization of the combustion chamber can achieve the emission standard of the
future. The Honda on its EXP-2 model achieved an optimization of the combustion
process that has never happened till date in petrol engine.
5. ACTIVE RADICAL COMBUSTION
In simple terms, auto
ignition bums up all the fuel in the cylinder. We currently associated with
engine knock, a phenomenon that occurs when the fuel ignites before the spark
plug fIres with the piston still on the up-stroke. This is caused when the
temperature & pressure in a cylinder build up to a critical point and the
air/fuel mixture explodes prematurely. Honda has tamed this pre-ignition on the
EXP-2, which otherwise destroy a normal two stroke engine. Using premature
combustion to more thoroughly bum the mixture is not a new idea- diesel don't
have spark plug either. But it is for the fIrst time that this technology has
been applied to 2-stroke petrol engine . The EXP-2 engine dose not use the
spark plug above idle and below 40% throttle.
5.1 PRINCIPLE OF (A R C) : -
When fuel is brought to the
right pressure & temperature; molecule breaks down into what are known as
active radical molecules. These are highly unstable chemical compounds. Formed
as an intermediate step in the actual combustion reaction. When hot exhaust
gases remains in the cylinder the small percentage of active radical molecules
combines with the incoming fuel charge & begins to auto ignite at a lower
temperature than a pure petrol/air mixture.
The fig. 1 indicates the combustion process in a
Honda EXP-2
1. Fresh fuel (white) enters the combustion chamber,
pushing the exhaust (gray) out the open exhaust valve in opposite side of the
cylinder.
2. The incoming fuel mixes with the exhaust &
some pockets of fuel are isolated within the exhaust. The exhaust valve closes
& the compression of the mixture is increased as the piston travels
upwards.
3. The fuel/exhaust mixture is compressed & auto
ignites as the piston reaches the top· of its stroke. This bums all the fuel,
and reduces the emission of unbent hydrocarbons into the environment. At small
throttle openings, a conventional two stroke will start a repeating pattern of
misfiring, which allows a large amount of unbent gas and oil to be expelled
directly into the atmosphere. At these low engine speed, the mixture not ignite
by the spark is the expelled directly into the exhaust system. Each time this
misfiring occurs, the amount of fuel remaining in the cylinder increase, until
it is great enough to be ignited by the spark. But the EXP-2 ignites the entire
mixture without the use of spark
at low & medium loads and is able to bum off and
oil in the cylinder in every cycle, eliminating the possibility of misfire and
reducing hydrocarbon emissions. This 400-cc single cylinder not only uses the
ASDI and active radial combustion but a trapping valve too. This is a new
technology ion the design of exhaust valve for two-stroke engine.
6.
TRAPPING
VALVE
These type of exhaust valve system restrict the
exhaust port at low r.p.m. and retract to uncover the exhaust port at high
r.p.m.. They trap the unburned gases that’s scavenge out the burned gases from
the combusion chamber before they can escape into the exhaust pipe. An engine
equipe with sush a system delivers more power at low end and mid range without
the use of an expansion chamber. This system is KAWASAKI
KX250. In the EXP-2 as shown in cut way section of the exhaust port ,
the valve is raised and lowers the top of the exhaust port , their by decreasing and increasing the fuel mixture
pressure in the cylinder as needed. By setting valve position base on the engine
rpm and throttle position , the pressure required for auto ignition can be
achived at exactly right timing , causing all fuel in the cylinder burn
completely.
7. CONCLUSION
Thus by using these
three technology, Honda EXP-2 produces 54 Hp and a 65N-m torqe making it one of
the best motocross racing bike.This was proved at the Granda-Dakar rally ,
where it was adjusted first in both under 500-cc and 2-stroke class , 8 over
all in Nevada rally and 7 over all Bajaj 1000. Honda will start the production
of the worlds cleanest 2 stroke motor cycle by the end of this year.
The Bimoto 500 V due a 500cc
2-stroke V- twine using the ASDI and trapping valve technology produces 110hp @
8000rpm.It achives all this while remaining environment friendly.
Honda was initiated then production of
CR250, which is gaint leap in the manufacturers willingness to implement new
patent in to production bike evolution.
We would definitely in years
to come notice bikes and scooter make use of this kind of technology bringing
the rebirth of 2-stroke engine as an environment friendly machine.
