Internal combustion engine-their evolution
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31-05-2010, 10:04 PM
ENGINES.ppt (Size: 2.19 MB / Downloads: 638)
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel (generally, fossil fuel) occurs with an oxidizer (usually air) in a combustion chamber. The expansion of high temperature and pressure gases produced by the combustion applies force to a movable component of the engine(piston, turbine blade etc.) moves it over a distance, generates useful mechanical energy.
GASOLINE DIRECT INJECTION:
The major advantages of a GDI engine are increased fuel efficiency and high power output. In addition, the cooling effect of the injected fuel, and the more evenly dispersed mixtures allow for more aggressive ignition timing curves. Emissions levels can also be more accurately controlled with the GDI system. The cited gains are achieved by the precise control over the amount of fuel and injection timings which are varied according to the load conditions. In addition, there are no throttling losses in some GDI engines, when compared to a conventional fuel injected or carbureted engine, which greatly improves efficiency, and reduces 'pumping losses' in engines without a throttle plate.
-Adding this function to the EMS requires considerable enhancement of its processing and memory, as direct injection plus the engine speed management must have very precise algorithms for good performance/driveability.
-The engine management system continually chooses among three combustion modes: ultra lean burn, stoichiometric, and full power output. Each mode is characterized by the air-fuel ratio. The stoichiometric air-fuel ratio for petrol (gasoline) is 14.7:1 by weight, but ultra lean mode can involve ratios as high as 65:1 (or even higher in some engines, for very limited periods). These mixtures are much leaner than in a conventional engine and reduce fuel consumption considerably
Ultra lean burn mode is used for light-load running conditions, at constant or reducing road speeds, where no acceleration is required. The fuel is not injected at the intake stroke but rather at the latter stages of the compression stroke, so that the small amount of air-fuel mixture is optimally placed near the spark plug. This stratified charge is surrounded mostly by air which keeps the fuel and the flame away from the cylinder walls for lowest emissions and heat losses. The combustion takes place in a toroidal (donut-shaped) cavity on the piston's surface. This technique enables the use of ultra-lean mixtures impossible with carburetors or conventional fuel injection.
Stoichiometric mode is used for moderate load conditions. Fuel is injected during the intake stroke, creating a homogenous fuel-air mixture in the cylinder. From the stoichiometric ratio, an optimum burn results in a clean exhaust emission, further cleaned by the catalytic converter.
Full power mode is used for rapid acceleration and heavy loads (as when climbing a hill). The air-fuel mixture is homogenous and the ratio is slightly richer than stoichiometric, which helps prevent knock (pinging). The fuel is injected during the intake stroke.
IN TWO STROKE ENGINES
Two types of GDi are used in two-strokes: low-pressure air-assisted, and high pressure. The former, developed by Orbital Engine Corporation of Australia (now Orbital Corporation) injects a mixture of fuel and compressed air into the combustion chamber. When the air expands it atomizes the fuel into 8-micrometre droplets, very small relative to the 20 to 30-micrometre fuel droplets in other direct injection systems. The Orbital system is used in motor scooters manufactured by Aprilia, Piaggio, Peugeot and Kymco, in outboard motors manufactured by Mercury and Tohatsu, and in personal watercraft manufactured by Bombardier Recreational Products (BRP).
In the early 1990s, Ficht GmbH of Kirchseeon, Germany developed a high-pressure direct injector for use with two stroke engines. This injector was unique in that it did not require a high pressure pump but was still capable of generating enough pressure to inject into a closed combustion chamber. Outboard Marine Corporation (OMC) licensed the technology in 1995 and introduced it on a production outboard engine in 1996. OMC purchased a controlling interest in Ficht in 1998.Beset by extensive warranty claims for its Ficht outboards and prior and concurrent management-financial problems, OMC declared bankruptcy in December 2000 and the engine manufacturing portion and brands (Evinrude Outboard Motors and Johnson Outboards), including the Ficht technology, were purchased by BRP in 2001.
Code named Bobcat the new twin-fuel engine from Ford. It is based on a 5.0L V8 engine block, but it uses E85 cylinder injection and gasoline port injection. The engine was co-developed with Ethanol Boosting Systems, LLC of Cambridge, Massachusetts, which calls its trademarked process DI Octane Boost. The direct injection of ethanol increases the octane of regular gasoline from 88-91 octane to more than 150 octane. The Bobcat project and implimentation was unveiled in Department of Energy and Society of Automotive Engineers in April 2009.
The common rail system was developed in the late 1960s by Robert Huber of Switzerland. After that, the technology was further developed by Dr. Marco Ganser at the Swiss Federal Institute of Technology in Zurich, later of Ganser-Hydromag AG (estb. 1995) in OberÃ¯Â¿Â½geri. In the mid-nineties, Dr. Shohei Itoh and Masahiko Miyaki, of the Denso Corporation, a Japanese automotive parts manufacturer, developed the Common Rail Fuel System for Heavy Duty Vehicles and finally turned into its first practical use on their ECD-U2 Common Rail system, which was mounted on the Hino Rising Ranger truck and sold for general use in 1995
Solenoid or piezoelectric valves make possible fine electronic control over the fuel injection time and quantity, and the higher pressure that the common rail technology makes available provides better fuel atomisation. In order 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 optimising injection timing and quantity for variations in fuel quality, cold starting, and so on. Some advanced common rail fuel systems perform as many as five injections per stroke.
Common rail engines require no heating up time and produce lower engine noise and emissions than older systems.
Diesel engines have historically used various forms of fuel injection. Two common types include the unit injection system and the distributor/inline pump systems. While these older systems provided accurate fuel quantity and injection timing control they were limited by several factors:
PRINCIPLE & WORKING
Modern common rail systems, whilst working on the same principle, are governed by an engine control unit (ECU) which opens each injector electronically rather than mechanically. This was extensively prototyped in the 1990s, with collaboration between Magneti Marelli, Centro Ricerche Fiat and Elasis. After research and development by the Fiat Group, the design was acquired by the German company Robert Bosch GmbH for completion of development and making suitable for mass-production. In 1997 they extended its use for passenger cars. The first passenger car that used the common rail system was the 1997 model Alfa Romeo 156 1.9 JTD and later on that same year Mercedes-Benz E 320 CDI.
They were cam driven and injection pressure was proportional to engine speed. This typically meant that the highest injection pressure could only be achieved at the highest engine speed and the maximum achievable injection pressure decreased as engine speed decreased. This relationship is true with all pumps, even those used on common rail systems; with the unit or distributor systems, however, the injection pressure is tied to the instantaneous pressure of a single pumping event with no accumulator and thus the relationship is more prominent and troublesome.
They were limited on the number of and timing of injection events that could be commanded during a single combustion event. While multiple injection events are possible with these older systems, it is much more difficult and costly to achieve.
For the typical distributor/inline system the start of injection occurred at a pre-determined pressure (often referred to as: pop pressure) and ended at a pre-determined pressure. This characteristic results from "dummy" injectors in the cylinder head which opened and closed at pressures determined by the spring preload applied to the plunger in the injector. Once the pressure in the injector reached a pre-determined level, the plunger would lift and injection would start.
Low Fuel Consumption
Lower pollutants in Exhaust gas.
Quiet Running of the Engine.
Improved Engine Performance.
This engine also have few disadvantages. The key disadvantage of the CRDi engine is that it is costly than the conventional engine. The list also includes high degree of engine maintenance and costly spare parts.
COMMON RAIL TODAY:
Today the common rail system has brought about a revolution in diesel engine technology.Ã‚Â Robert Bosch GmbH,Ã‚Â Delphi Automotive Systems,Denso Corporation, andÃ‚Â Siemens VDOÃ‚Â (now owned by Continental AG) are the main suppliers of modern common rail systems. The car makers refer to their common rail engines by their ownÃ‚Â brandÃ‚Â names:
M.P.F.I. means Multi Point Fuel Injection system. In this system each cylinder has number of injectors to supply/spray fuel in the cylinders as compared to one injector located .
ADVANTAGES OF MPFI:
1) More uniform A/F mixture will be supplied to each cylinder, hence the difference in power developed in each cylinder is minimum. Vibration from the engine equipped with this system is less, due to this the life of engine components is improved.
(2) No need to crank the engine twice or thrice in case of cold starting as happens in the carburetor system.
(3) Immediate response, in case of sudden acceleration / deceleration.
(4) Since the engine is controlled by ECM* (Engine Control Module), more accurate amount of A/F mixture will be supplied and as a result complete combustion will take place. This leads to effective utilization of fuel supplied and hence low emission level.
(5) The mileage of the vehicle will be improved.
ECM ( Engine Control Module) and its function
The function of ECM is to receive signal from various sensors, manipulate the signals and send control signals to the actuators.
Sensors; Sensing different parameters (Temperature, Pressure, Engine Speed etc.) of the engine and send signal to ECM.
Actuators; Receives control signal from ECM and does function accordingly (ISCA, PCSV, Injectors, Power Transistor etc.)
Case I: If ECM fails to send control signal to all actuators then the engine won't get started.
Case II: If ECM fails to service from all sensors then also the engine won't get started.Ã‚Â
MPFi V/S CRDi:
MPFI : mean multi point fuel injection system ie. in petrol engine for gaining more uniform Air Fuel blending fuel is injected at various point in the path of air. this tech is used in light weight car running on petrol. there is also milage improvement due to this.
but in case of DTSI(digital twin spark ignition) : the
engine cylinder consist of two no of spark plug for proper combustion of charge.
DTSI : It is the DIGITAL TWIN SPARK IGNITION system
The principle of operation is that, there is an additional SPARK PLUG introduced at the other end of the combustion chamber along with the usual spark plug with the the traditional placement at the top centre.
The idea was introduced considering the SLOWER Flame Propogation with only one Spark Plug as in traditional engine design.
Also due to the rectangular shape of the Combustion Chamber the Flame could not reach all the sides and corners regions of the Combustion Chamber, thus leaving some amount of the A/F mixture UNBURNT.
Both the above points were a drawback resulting in :
Slower and Incomplete burnig of the A/F mixture thus Producing LESSER POWER, LOWER FUEL EFFICIENCY and HIGHER HC EMISSIONS.
By introducing the DTSI, due to Two Spark Plugs at two opposite ends of the Combustion chamber, there is:
Faster and More Precise Flame Propogation and,
Better reach of the Flame covering more chamber space resulting in Greater amount of mixture burned in a more even manner.
There is also Swirl Induction incorporated at times for bettermixing inside the combustion Chamber and give better Burning of the fuel.
Both these Improvisations lead to Higher Fuel Efficiency and Higher Power and Torque Developed.
This considerably Improves the Engine Performance, than
the traditional FI systems.
The Engine Power and Torque is believed to improve by nearly 8% by using DTSI
Also the DTSI is combined with the COMPUTERISED DIRECT IGNITION or CDI which is an eight bit microprocessor chip with preprogrammed maps of Ignition Timings for various engine rpms and engine loads.
The CDI works along with the THROTTLE RESPONSIVE IGNITION CONTROL SYSTEM. This TRICS controls the Ignition based upon the Amount of Throttle Opening.
Thus when the rider Accelerates suddenly or goes on a smooth uniform drive mode, the Ignition requirement varies acccordingly
Hence the Throttle openig also changes, this is sensed by the TRICS which accordingly opens and closes the Reed Switch operated magnetically. This TRICS is connected to the CDI which inturn controls the IGNITION SPARK ADVANCE AND TIMING thus giving a much efficient SPARK ADVANCE for every engine rpm and load conditions.
This eventually increases the Engine Performance and Fuel
Efficiency of the vehicle and reduces the HC Emissions
MPFI : It is the MULTIPORT FUEL IGNITION system.
In this there is at least ONE INDIVIDUAL FUEL INJECTION NOZZLE/PORT for EVERY INDIVIDUAL CYLINDER of the Engine as opposed to the ONE CENTRAL FUEL PORT in the traditional Engine design.
The basic idea is to provide better ratio of A/F mixture in every cylinder nearing the Stoichiometric Value of 14.7 : 1 as far as possible for all various speeds (rpm) and acceleration demands. This was not so much achievable with the single central fuel port system.
This system allows to have a desired A/F ratio for demand condition, thus almost eliminating the A/F distribution issues.
The MPFI includes intake runner length adjustments, MAF
( Mass Air Flow) sensors, coupled to the ECM
( Electronic Control Module ).
The Longer intake runners are for Low Torque Demand in normal road driving, amd Shrter Intake runner for Sudden High Rpms and Acceleration requirements.
The MAF sensors are situated between the Air Filter and the Throttle body in the Intake Manifold. This sensor accurately measures the Air Flow Rates into the engine ( which is an indication of the engine rpm) and sends the feedback to the ECM which inturn does the PROPER FUEL METERING .
Thus a correct A/F ratio can be achieved in each cylinder. This inturn assures
a better fuel Efficiency,
greater power output for same mixture ratio,
a much better control over the A/F ratio as per te instanteneous speed demand.
Overall better performance.
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28-02-2011, 02:57 PM
The IC Engine.ppt (Size: 167.5 KB / Downloads: 224)
The IC Engine: Why…
The internal combustion engine was first conceived and developed in the late 1800’s
The man who is considered the inventor of the modern IC engine and the founder of the industry is pictured to the right….Nikolaus Otto (1832-1891).
Otto developed a four-stroke engine in 1876, most often referred to as a Spark Ignition, since a spark is needed to ignite the fuel air mixture
The impact on society is quite obvious, all most all travel and transportation is powered by the IC engine: trains, automobiles, airplanes are just a few.
The IC engine largely replaced the steam engine at the turn of the century (1900’s)
Another important cycle is the Diesel cycle developed by Rudolph Diesel in 1897. This cycle is also known as a compression ignition engine.
Background on IC Engines
“An internal combustion is defined as an engine in which the chemical energy of the fuel is released inside the engine and used directly for mechanical work, as opposed to an external combustion engine in which a separate combustor is used to burn the fuel.”1
“IC engines can deliver power in the range from 0.01 kW to 20x10^3 kW, depending on their displacement.”2
Background on the Otto Cycle
The Otto Cycle has four basic steps or strokes:
1. An intake stroke that draws a combustible mixture of fuel and air into the cylinder
2. A compression stroke with the valves closed which raises the temperature of the mixture. A spark ignites the mixture towards the end of this stroke.
3. An expansion or power stroke. Resulting from combustion.
4. An Exhaust stroke the pushes the burned contents out of the cylinder.
To the right is an idealized representation of the Otto cycle on a PV diagram.
The Otto cycle IC engine has remained fundamentally unchanged, besides slight improvements, for over 100 years. Its’ popularity has continually increased because…
Relatively low cost
Favorable power to weight ratio
Relative simple and robust operating characteristics
Improvements are mainly lower emissions and higher fuel efficiency
mep= work done per unit displacement volume
Or average pressure that results in the same amount of indicated or brake work produced by the engine
Scales out effect of engine size
Two useful types: imep and bmep
imep: indicated mean effective pressure
-the net work per unit displacement volume done by the gas during compression and expansion
bmep: brake mean effective pressure
-the external shaft work per unit volume done by the engine
Based on torque:
Brake specific fuel consumption (bsfc)
Measure of engine efficiency
They are in fact inversely related, so a lower bsfc means a better engine
Often used over thermal efficiency because an accepted universal definition of thermal efficiency does not exist
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18-03-2011, 10:46 AM
M Sesha Srinivas
seminar2003.ppt (Size: 1.16 MB / Downloads: 172)
Internal Combustion Engines
Engine: a device that transforms different forms of energy
Heat Engine: a device that transforms chemical energy of fuel into thermal energy which is utilised to perform useful mechanical work
CLASSIFICATION OF HEAT ENGINES
Combustion process takes place inside the cylinder
Reciprocating IC Engine
that uses one or more reciprocating pistons to convert pressure into a rotating motion
Engine Cylinder block
MOVING PARTS OF AN ENGINE
Working of an IC Engine
Four Stroke Combustion Cycle
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08-10-2012, 11:14 AM
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