MARINE CURRENT TURBINES AN EFFICIENT RENEWABLE SOURCE OF POWER

MARINE CURRENT TURBINES AN EFFICIENT RENEWABLE SOURCE OF POWER

Just as there were a no. of water mills across several countries in the medieval period that had helped power the rural economy and then the industrial revolution. And just as wind power was taken to be a savior for greener energy, this new technology known as Marine Current Turbine is posed to power the world in the 21^st century. This paper essentially deals with this new form of power generation as an effective alternative to conventional sources of power. These turbines are cost effective as they employ reinforced plastics as the building material. This form of power generation is more reliable than its counterpart on land which, is of course, wind power generation. This form of power generation is not affected by tides, cyclones and tsunamis since the operation is usually done in continental reef region of the sea. Further, its operation has been declared successful in the North Sea. Further onsite testing of the prototype is done in and around Sweden and Britain. The power generated from this source can also be used for desalination of sea water for domestic supply.

KEYWORDS

PROTO TYPE

TIDAL TURBINE

SOLAR POWER

WIND MILL

PLASTIC BASED MATERIAL

MARINE CURRENT TURBINES

INTRODUCTION:

During the past few decades the advanced technology nations of the world have been engaged in an energy and resources race that has brought us to the position of a global energy crisis. The most intriguing fact is that even the so-called third world countries have also caught up with this race and the situation is getting worse than ever. 'This has brought us to a very strange scenario that makes us believe as if our dooms day is not far off. To prevent this avoidable mishap, many scholars have taken up research to find greener sources of power which has brought us to the cross-roads of technologies. To keep pace with the ever increasing power demand and detoriating environmental conditions and depleting resources we have developed many promising new ideas some of which are solar power, wind power, tidal power, fusion energy, geo­thermal power, ocean thermal power, MHD, etc.

The most promising of these is however a radical new look to the older watermills known as Marine Current Turbine (MCT) or Tidal Turbine. We are going to see how this new technology could be used to produce a greener source of power, in this paper.

MARINE CURRENT TURBINE:

Harnessing power from flowing water in the 21 S' century may be anything between one & two decades behind wind power, but the technology has moved beyond the conceptual stage, has shown that it works in pilot installations and is poised to progress to initial commercial exploitation. Companies in the forefront in this field have already commenced the construction of prototypes in many parts of the world & even a prototype in northern Norway has begun production on commercial lines. This paper essentially deals with the principles &various bottle necks in establishing economically & ecologically profitable operation of these MCTs.

PRINCIPLE:

MCT basically involve the same concepts & principles involved in the construction of wind turbines. The Kinetic energy of per unit volume of water is 'h pv² (p is the density of water molecules, v is their velocity).For a surface area A, this energy means an energy of 1/2 pv²A per unit distance in the direction of current. The energy is converted along the direction of v This means the energy per second i.e., power is '/2 pv³ But one thing we can be sure of is that not all this energy can be extracted .To extract all the energy the current velocity has to be brought to zero. This would in turn mean an accumulation of water around the turbine which is something next to impossible. Conventional turbines can be made to operate with an efficiency anywhere between 35-45 % which would mean an extraction of .45 Kw/m² for a current velocity of 10 mands which is the current velocity at its mean.

WIND VERSUS SEA:

We can definitely say that both wind flow & underwater-current flow have much to share as common-properties. Both follow the laws of fluid mechanics. Both convert kinetic energy from a moving fluid (or gas, in air's case), first into mechanical energy and then into electrical energy. Both have a rotor with two or more blades driving a generator via a shaft and a gearbox. Most `windmills' and so far `watermills' too, are horizontal -axis machines. In both cases, the cube law operates, power extractable being proportional to the velocity of the fluid medium passing through the rotor, raised to the power of three (v³). Although the rotors may visually suggest scaled air-craft propellers, they turn relatively slowly are driven by the, flow rather than driving it, and operate in very different order of flow speed. One similarity however, is that it is important to optimize the blade's aero/hydro-dynamic shape for efficient operation. Both wind and water rotors require pitch control so that their blades can be adjusted to flow conditions. Both also need support structures so that the rotors can be positioned in a favour regime. In short a very simple overview may give us the fact that MCT are nothing but new avatars of successfully proven models of wind turbines.

BOTTLE-NECKS:

An irrefutable fact is that there are also many great differences between wind and MCT. One is that marine current turbines are designed to capture the flow in just two directions. Since tides are lunar driven and reverse their direction every six and a quarter hours, rotors may simply be reverse to face the new current, or accommodate the change with a blade pitch `reversal'. Wind rotors, on the other hand, must generally yaw so as to face the wind from any direction.

The most striking dissimilarity, though, is due to massively higher density -832 times that of air. In the long, slender blades of wind turbines, centrifugal forces dominate and these tend to restrict bending. In water-turbines, however because they operate in a much denser medium, bending ' loads dominate, and these tend to bend the blades of the turbines. For example, a 1 MW tidal flow machine might have anything up to 100 tones of thrust on it, about double that it would be for a similarly rated wind machine. To keep these bending loads manageable, marine turbine blades are relatively short and flat. Because marine rotors are of limited diameter and rotate slowly, there is little centrifugal force to react the bending.

Further , water flows at a lower rate than wind -for example, a MCT might be rated to a maximum power in a current of 2.3 m/s (or 4.5 knots), compared with a typical 12-13 m/s flow for wind. But this in no way compensates for the density difference. Whereas a 1MW water turbine would have some 30-40 tonnes of air pass through the cross-section of its rotor when at full power, a 1 MW water turbine operating at 4.5 knots tide sees over 900 tonne of water pass through its rotor. Designing to accommodate these flow rates over a lifetime of 20-30 years is a challenge. Structures for

marine turbines must also be stressed to withstand transient forces caused by turbulence as by passing surface waves.

MATERIAL CHOICE:

Sub-marine structures also have to withstand the notoriously aggressive marine environment with its corrosive salt water, fouling growth and abrasive suspended particles. Designers first considered producing the required stiff, unyielding marine rotors in steel. However, achieving the necessary compound-curved profile in steel proved to be expensive. Moreover steel is very heavy, prone to fatigue and susceptible to corrosion induced by salt water. These disadvantages prompted a decision to adopt composites instead. Plastic-based materials ease the fatigue problem, both through their inherent fatigue tolerance and by reduced blade weight. Calculations also showed that appropriately applied, they could deliver the required stiffness. However, some wind blades rely solely on the form of stiffness of a sandwich envelope structure, a robust internal 'skeleton' was considered essential for their marine counterparts.

A two-blade configuration was chosen for the l lm diameter rotor of the Sea flow prototype. This was partly for practical reasons -a two-blade rotor attached to the turbine shaft and drive train forms a flat 'T' that can be readily laid on the deck of an installation barge and handled by cranes .

A RADICAL NEW METHOD

The blades can be built so as to derive most of their strengths from a robust carbon fiber main spar that can be bonded with a glass-fiber composite envelope that will give the blade its hydrodynamic shape. Carbon-reinforced ribs, attached perpendicularly to the spar, will help in transmitting loads from the load. Here glass is chosen as it is impact resistant (also shatter-proof) and affordable. Also foams impregnated with carbon fibers & epoxy cloths can be used for the same purpose.

Keeping blistering at bay for longer periods is a very difficult task for which high quality laminate with low void content and incorporating non-hydrophilic epoxy resin is a good starting point, while innovative finishes that also resist marine growth are being considered.

THE POTENTIAL:

This new technology has a lot of potential to light the entire planet with the power it generates. As we all know ours is a blue planet with a lot of potential places where such MCT can be established. For example an assessment study conducted by a private firm in and around Britain has found that the country has got more power than it could ever consume. Such a study along the coastal creeks and under­water hills around our country could easily establish the fact that even we've got equal potential. Since this source of power doesn't consume any kind of fuel, operating these turbines will also prove to be much more economical.

ECOLOGICAL IMPACT:

This technology represents a novel method for generating electricity from a huge energy resource in the sea. It is rare enough for an entirely new energy resource to be developed but even rarer if the technology, as in this case:

• produces no pollution and has negligible environmental impact
• delivers energy to a predictable timetable
• has the potential to make a major contribution to future energy needs

Although the relentless energy of marine currents has been obvious from the earliest days of seafaring, it is only now that the development of modern offshore engineering capabilities coinciding with the need to find large new renewable energy resources makes this a technically feasible and economically viable possibility.

The rationale for developing this business is based on three robust arguments:

• The world needs more energy, yet this will have to be clean renewable energy in line with the Kyoto Protocol and "Agenda 21" (most governments world-wide are committed to this) and Marine Current Turbines can deliver this

• The scope for meeting future energy requirements solely from land-based resources will be constrained by conflicts over land-use; so large renewable energy projects will need to move away from crowded land areas - it is significant that the wind

industry is also moving offshore, yet many potentially energetic marine current sites are not far from large electricity markets

• the nearest competitor is wind-electricity generation, which has grown from almost nowhere ten years ago, into a multi-billion dollar industry; the marine current energy resource has the potential for exploitation to equal or exceed wind energy in its future importance
• MCTs do not emit or produce any greenhouse gases, harmful waste, or pollutants during operation (e.g. C02, NOx and SOx).

• Compared to offshore wind farms visual disturbance at sea will be low. The only indication of the presence of MCTs would be the surface piercing structures with navigational-buoyage equipment, and this will be located some distance from the coastline.
• The low frequency sub-sea noise that would be emitted during operation would not interfere with the echolocation capability of cetaceans and also serve to warn marine mammals to keep away.
• The minimal effects from installation are only temporal and any sea life displaced would soon return.
• As fishing and recreational and commercial access within MCT zones would be prohibited, schemes may act as protective man-made reefs in which wildlife may flourish. This could bring serious benefits to endangered species and fragile fish stocks.

Environmental Impact Analyses completed by independent consultants have confirmed our belief that the technology does not offer any serious threat to fish or marine mammals. The rotors turn slowly (10 to 20 rpm) (a ship propeller by comparison typically runs 10 times as fast and moreover our rotors stay in one place whereas some ships move much faster than sea creatures can swim). There is no significant risk of leakage of noxious substances and the risk of impact from our rotor blades is extremely small bearing in mind that the flow spirals in a helical path through the rotor and that nature has adapted marine creatures so that they do not collide with obstructions (marine mammals generally have sophisticated sonar vision). Another advantage of this technology is that it is modular, so small batches of machines can be installed with only a small period between investment in the technology and the time when revenue starts to flow. This is in contrast to large hydro electric schemes, tidal barrages, nuclear power stations or other projects involving major civil engineering, where the lead time between investment and gaining a return can be many years.

Further, independent analysis by American Fisheries Society which earlier had some reservations regarding tidal power generators, has given an almost clean chit for this type of projects. Another encouraging fact is the potentially less retention of sea water when compared to that of tidal water turbines.

CONSTRAINTS:

• The main visual disturbance would be land-based electrical substations and over­head lines.
• Public may be concerned with the risk of the turbine rotor colliding with fish or mammals. However this is unlikely because small and medium sized creatures would tend to be pushed out of the way by the blades (due to fluid dynamics) and larger mammals, such as seals, whales and dolphins, are known to avoid ships and ships propellers and could be expected to exhibit that same behavior with MCT. Also, a ship's propeller, which is accepted without question for widespread use at sea, is a far greater hazard as it rotates at far greater speeds, e.g. up to 10 times faster, and it is attached to a moving vessel that may travel faster than the fauna.
• Seismic surveys and blasting prior to installation could create frequency waves that may have negative effects on the health of fish and marine mammals.

• Installation of cables may also cause sediment displacement, which in turn could cause dangerous particles to be dispersed and contaminate the local environment e.g. radioactive particles discharged from Dounreay. Proposed sites would have to be analyzed for contaminants.
• During operation of the MCT, the pile would experience increased scouring around its base caused by increased turbulence affecting the seabed morphology.
• Possible discharge of oil from the gearbox or the anti-fouling paint used to prevent bio-fouling may pollute.
• Current flow and coastal processes could be affected because an oversized scheme could act as a barrier to the oncoming current. Attempting to extract too much energy from a tidal stream could cause the tide to divert to an easier path.

The exact environmental impact of a Marine Current Turbine has not '!et been assessed therefore it is not possible to quantify the exact impact an array of turbines may have on the ecology, environment and existing users. however. installing a monopole -mounted to-meter diameter turbine in water up to 50 meters deep would inevitably have some impact, possibly negative or positive on the surrounding environment. The level of impact would be determined by the quantity of units installed and the packing density.

The second strategy, which selected the maximum number of units that could be installed thus maximizing the storage required, would result in maximum environmental impact. The first strategy, which compromised the number of installed units with the aim of reducing the storage required to an acceptable level, would have a less impact.

The technology used to secure the turbine to the seabed may also have differentimpacts. For example, the proposed first-generation of MCT uses mono piles which could destroy seabed habitats during installation. A second-generation design could use mooring systems, which may have less of an effect on seabed wildlife whilst allowing the turbines to operate in deeper waters.

The density in which units are installed may also influence any environmental effects. For example, drilling monopoles, of a significant distance apart may reduce impact of erosion caused by scouring around the base of the monopoles on wildlife. The MCT parametric model and packing density selected in this project means that across the tidal flow, turbines with diameters of 15.85-metres would be spaced out some 60-metres apart.

This would leave a minimum gap of 44 meters from blade tip-to-tip. The turbines would be positioned 1000-metres downstream from each other in order to reduce the negatives effects on performance caused by turbulence and allow for the tidal streams to restore themselves, The horizontal and axial spacing would result a packing density of 18 units per km2, which could allow for tidal stream, the various wildlife and larger mammals to pass through unaffected.

The layout of arrays of MCT could also influence the impact. For example, rows of turbines located besides each other may act as a larger barrier to oncoming tidal stream compared to farms where the turbines are installed in scattered arrays.

Waters of depths from 20 to 80 meters chart datum would be used; therefore any wildlife or marine activities using water in depths outside this range would not be directly affected.

CONCLUSION:

With increasing pressure from the environmentalists and acute shortage of power due to uncertainty in the political status of the middle-east, the world cannot simply thrive on the hope that these conventional sources of power will continue to supply all our needs for posterity. In the wake of this crisis we can be sure that this new MCT technology will power the world in the near future as is the thermal power in the present day world. For, no one believed that day, when Faraday told that we can collect revenue by generating power. It is because of these new and innovative ideas that the present world is as it is today. The day is not far away, for

RENEWABLE POWER GENERATION THROUGH SAVONIUS ROTOR (VERICAL AXIS WIND TURBINE)

RENEWABLE POWER GENERATION THROUGH SAVONIUS ROTOR (VERICAL AXIS WIND TURBINE)

RENEWABLE POWER GENERATION THROUGH SAVONIUS ROTOR (VERICAL AXIS WIND TURBINE)

OPTIMISATION OF SAVONIUS (VERTICAL AXIS) TURBINE

FOR RENEWABLE POWER GENERATION

INTRODUCTION:

Our present work describes the modification in design of the savonius rotor system which is simple in design , fabrication, maintenance and more suitable for small scale power generation applications. Savonius turbines are self starting, inexpensive and is least sensitive to wind direction which makes it more reliable for both urban and rural applications.

NEED FOR SAVONIUS WIND TURBINE SYSTEMS:

# The normal wind mills (axial) require a tower of 50- 70 m height.

# They require a large space owing to their large rotor vane (diameter ) span.

# They shut down during heavy or low turbulent wind conditions.

# They require a starter motor to overcome the initial inertia of the large rotor.

# They need an exclusive YAW mechanism for changing the direction of rotor against wind.

# They require a steady wind pattern so they cannot be installed everywhere.

All these draw backs of the normal axial wind mills favour the improvisation of savonius rotor and make our design a valid one.

BASIC SAVONIUS ROTOR SYSTEM:

The Savonius rotor is a vertical axis wind turbine with high starting torque. Its use has been limted till now because of the poor aerodynamic shape of rotor. Nevertheless these type of rotors are self starting , simple to construct and least sensitive to wind direction. So modifying it improve its overall performance would increase its potential of small scale power generation.

# 2 – 6 bladed radial turbine .

based on eqn :- No. of Blades = 8.5 (sin β) / (1 – r1 /r2)

# mainly uses drag rather than lift like Darrius rotor (vertical axis).

# doesn’t require a huge space like axial rotors (normal wind mills).

MODIFICATIONS DONE :

The following modifications are done inorder to increase the overall performance of the rotor.

i) Twisting the blades

ii) Back valves to reduce opposite drag

iii) Funneling the shaft

iv) Improving the aerodynamic shape

TWIST ANGLE OF THE BLADES:

The twisted blades offer low turbulence comparing to normal straight blades which contributes to the increase in the rotor speed. The blade profile is designed in such a way that the wind enters through the lower half and exits through the upper half with a streamlined flow. θ = 30 – 40 deg depending on the width of the blades.

# turbulence of the air flow is reduced .

# The twist angle makes the rotor insensitive to direction of the wind.

BACK VALVES :

# Reduces the opposite drag and prevents the back flow (acts like a NRV valve) and so

increases the speed

# It is designed in such a way that it can open only upto an angle of 30-45 degree.

The working of the valves :

* The valves shut down when the vane moves along the direction of the wind so that it increases the favourable drag.

* The valves open when they move opposite to the direction of the wind current thus reducing the opposite drag.

FUNNEL SHAPED SHAFT :

The shaft is funnel shaped so that the wind entering the lower half of the twisted vanes go through them without causing any turbulence. This reduces the overall turbulence and so reduces the opposite drag.

AERO DYNAMIC ROTOR :

To improve the aero dynamic characteristics and to reduce the opposite drag , thus increasing the overall efficieny.

CUSTOMISATION :

Through various design research and developments , the savonius rotor system can be customized into various forms. It could be incorporated onto an automobile or setup on top of a sky scraper or as a portable vertical axis wind mill.

CONCLUSION:

Thus we have proposed three major modifications in the savonius rotor which would increase the overall efficiency by 5-10 %. The main reason behind this paper is to create an awareness about this savonius among rural small scale power generation sector thus reaching another step in renewable power generation.

DUAL FUEL SIX STROKE ENGINE WITH EGR TECHNOLOGY

DUAL FUEL SIX STROKE ENGINE WITH EGR TECHNOLOGY

ABSTRACT

The Present scenario of Fuel Consumption is well known to everyone. Everyday technical people talk about the depleting Fuel sources and Exhaust hazards. Particularly about the Diesel engines find their importance more than the Petrol engines due to their operating cost and Fuel consumption But Diesel engines have their demerits in the area of Exhaust and Power loss. Necessary steps have to be taken in order effectively use the Fuel available. We have brought the UTILIZATION OF SIX STROKE ENGINES which runs on DUAL FUEL to your view. The Six Stroke Engine’s Principle resembles the Double Stage Compressor. By this way effective Compression is done and the need for Turbocharger is completely neglected. We have also considered Cylinder’s position in Six Stroke engine. Also the Pollution (NOx) emitted by the Diesel Engines is also taken into account. We found the solution in the form of Dual fuel and Exhaust Gas Recirculationsystem. The Combusting Temperature is above 2000 F and this is the prime reason for NOx Emission. So an Alternative Fuel which can be combusted below the level of Diesel should be used. Moreover the availability and production cost must be taken into consideration. We found Ethanol as a better alternative for Diesel. The Cold Starting of the Engine is made easier using GLOW PLUG which is used to preheat the Charge coming inside the Combustion Chamber.

INTRODUCTION

In today’s world, the usage of Internal Combustion Engines is inevitable..Oxides of Nitrogen (NOx) are formed when Temperatures in the Combustion Chamber get too hot. At 2500 F, the Nitrogen and Oxygen in the Combustion Chamber can chemically combine to form Nitrous Oxides, which, when combined with Hydrocarbons (HCs) and the presence of Sunlight, produces harmful effects. In order to reduce these effects, a Dual Fuel technique is implemented in which ethanol is used as a Running Fuel which has less NOx emission than the Conventional Diesel Engines.

In order to achieve such a High Compression Ratio , Efficiency. Six Stroke CI engine is found to be more suitable. Starting of CI engines during cold weather becomes severe when compared to the SI engines. The conventional method of circulating hot water is being replaced by GLOW PLUG, thereby diesel consumption during starting period is reduced considerably and quick starting is achieved

Exhaust Gas Recirculation (EGR)

This system also gets added up in the list so as to reduce the NOx effect. A simple recirculation circuit dilutes the incoming charge in the inlet manifold thereby reducing the combustion temperature to some 100 degree which optimally reduces the NOx problem. We also had the idea of implementing Turbo charger, but usage of six stroke engine and EGR eradicated that idea.

SIX STROKE ENGINE

Considering the importance of cleaner, powerful and economical engine we have come up with this new idea for practical implementation of six stroke engine , which will be nearly 40% more fuel efficient than the existing four stroke engines. The engine is also more efficient and powerful than the existing six stroke and four stroke engines. The engine is also having the scope of using heavy fuels and bio-fuels.

The majority of the actual internal combustion engines, operating on different cycles have one common feature, combustion occurring in the cylinder after each compression, resulting in gas expansion that acts directly on the piston (work) and limited to 180 degrees of crankshaft angle.

According to its mechanical design, the six-stroke engine with external and internal combustion and double flow is similar to the actual internal reciprocating combustion engine. However, it differentiates itself entirely, due to its thermodynamic cycle and a modified cylinder head with two supplementary chambers . Combustion and an Air Heating Chamber, both independent from the cylinder. Combustion does not occur within the cylinder but in the supplementary combustion chamber, does not act immediately on the piston, and its duration is independent from the 180 degrees of crankshaft rotation that occurs during the expansion of the combustion gases (work).

The Combustion Chamber is totally enclosed within the air-heating chamber. By heat exchange through the glowing combustion chamber walls, air pressure in the heating chamber increases and generate power for an a supplementary work stroke. Several advantages result from this, one very important being the increase in thermal efficiency. In the contemporary internal combustion engine, the necessary cooling of the Combustion Chamber walls generates important calorific losses.

The engine has better turbulence due to which the combustion is smooth and effective. The engine has better air pollution control than existing four stroke engines. The engine may be smokier with heavy fuels but the pollution level when compared to the existing heavy fuel engines will be within limit. With the use of conditioned heavy fuels, this sulphur smoke can be dramatically reduced and pollution can be reduced considerably

BASIC ENGINE PARTS

Inlet Valve: when open supplies fresh air into the engine

Exhaust Valve: When open removes the burned gases from the engine

Combustion chamber Valve: The valve connects the cylinder with the combustion chamber. Opens to permit the flow of compressed air from the cylinder to the combustion chamber and also to permit the flow of exhaust gases from the combustion chamber to the cylinder to drive the power stroke.

Heating chamber Valve: The heating chamber has been provided with a valve, to release the pure air into the cylinder. The valve makes scavenging much more effective than what is found in the existing six stroke or four stroke engines.

Fuel Injector: Highly pressurized is injected into the combustion chamber.

Cylinder: Supplies compressed air to the combustion chamber. It also aids in providing better turbulence in the combustion chamber making combustion smooth and effective

Combustion Chamber: The combustion of the compressed fuel occurs with the aid of the fuel pumped into the cylinder.

Piston: moving in the cylinder, gets power from the exhaust of the combustion chamber and the air from the heating chamber

.

GLOW PLUG:--PREHEATER

To preheat the cylinder before starting. One such method is the circulation of hot water into the water jacket of the cylinder.Glow plug emerges as a very good alternative. A heating element is placed nearby the fuel injector, which is being supplied with a very high current of 25-35 amperesfor a period of 5 to15 seconds prior to the starting. The heat is transferred by means of combustion from the cylinder surface to the incoming air, thereby reducing time taken to heat the air medium.

WORKING OF A GLOW PLUG

Fuel blend assists in using a heater for a better running condition .High latent heat and low vapour pressure reduces the temperature of cylinder wall which necessitates the use of Glow plug.

THE STROKES:

FIRST STROKE

During the first stroke the inlet valve is opened and air is sucked into the compression

Chamber. The air is compressed in the combustion chamber.

SECOND STROKE

The heating chamber valve is opened and the air sucked in by the cylinder is compressed and send to the heating chamber. Simultaneously the fuel is injected in the combustion chamber. Thus the combustion takes place inside the combustion chamber

THIRD STROKE

The combustion chamber valve opens and the combustion gases is realased into the cylinder. The high pressure with which the exhaust gases are pushed out aids to obtain a power stroke. Simultaneously there is a heat exchange takes place between the combustion chamber and heating chamber which is filled with pure air.

FOURTH STROKE

The exhaust valve is opened, driving out the exhaust gases from the cylinder

FIFTH STROKE

By heat exchange through the glowing combustion chamber walls, air pressure in the heating chamber is increased. When the heating chamber value is opened the high-pressured air formed will enter the cylinder which will result in another power stroke.

SIXTH STROKE

When the combustion chamber valve opens, the expanded air is re-compressed and sends into the combustion chamber.

ADVANTAGES

• 30% reduction in fuel consumption and Two Power Strokes
• More powerful than the existing conventional engines.
• Heavy fuel Usage, Better Scavenging
• Dramatic reduction in pollution

FACTORS CONTRIBUTING TO ADVANTAGE:

1. The heat that is evacuated during the cooling of a conventional engine’s cylinder head isrecovered in the six-stroke engine by the air-heating chamber surrounding the combustion chamber.

2. After intake, air is compressed in the heating chamber and heated through 720 degrees of crankshaft angle, 360 degrees of which in closed chamber (external combustion).

3. The transfer of heat from the very thin walls of the combustion chamber to the air heating chambers lowers the temperature and pressure of the gases on expansion and exhaust(internal combustion).
4. Better combustion and expansion of gases that take place over 540 degrees of crankshaft rotation, 360° of which is in closed combustion chamber, and 180° for expansion.
5. The glowing combustion chamber allows the optimal burning of any fuel and calcinate the residues.
6. Distribution of the work: two expansions (power strokes) over six strokes, or a third more than the in a four-stroke engine.
7. Better filling of the cylinder on the intake due to the lower temperature of the cylinder walls and the piston head.
8. Elimination of the exhaust gases crossing with fresh air on intake. In the six stroke-engines, intake takes place on the first stroke and exhaust on the fourth stroke.
9. Large reduction in cooling power. The water pump and fan outputs are reduced. Possibility to suppress the water cooler.
10. Less inertia due to the lightness of the moving parts.

DUAL FUEL TECHNOLOGY

Dual fuel engine is one which operates with two different fuels. One is the igniting fuel (diesel) and other is the running fuel. We can find huge variety of running fuels from the present researches. One such fuel is ALCOHOL.

Under Alcohol, many types are found to satisfy the budding problem such as Methanol, ethanol, Butyl alcohol, etc. We Prefer Ethanol as the suitable running fuel because of the following properties listed..

Chemical formula	Chemical weight (kg/mole)	Specific gravity	Boiling point (C)	Latent heat (KJ/kg)	Combustion energy (KJ/kg)	Vapour pressure @100F (psi)	Solubility part in 100 parts H2O
CH3CH2(OH)	20.906	0.79	78	189.463	6296.332	2.2	infinite

Moreover some additional advantages related with ethanol are:

• It is not a fossil fuel (i.e.) combusting it does not cause any Green House Effect.
• It is Biodegradable which does not affect the environment.
• Higher oxygen content ultimately reduces the NOx emission and other harmful pollution
• The fuel is very much economical for long run.
• The compression ratio is high of the order 25-27.

Since the alcohols have very high self ignition temperature, so the design of the engine using ethanol as the primary fuel will be robust and expensive .So a general idea of using ethanol in dual fuel operation is practiced.

PRINCIPLE OF OPERATION

In dual fuel engine the alcohol is generally injected into the combustion chamber. Due to high self ignition temperature of alcohols, there will be no combustion with usual diesel compression ratios of 16-18. So a little before the end of compression stroke, a small quantity of diesel oil is injected into the combustion chamber through normal pumping techniques. The diesel oil readily ignites and this initiates combustion in the alcohol-air mixture also.

METHODS OF INJECTING ETHANOL

Methods used are pneumatic spray nozzle, vapourizer, carburetor and fuel injector.

Another important method that can be implemented is the direct injection of ethanol into the combustion chamber after the diesel fuel injection. By this way, alcohol cooling of the charge is avoided to a degree which will jeopardize the ignition of the diesel fuel.

This system requires two complete and separate fuel systems with their necessary fuel feed systems.

In the dual fuel engines, major portion of the heat release is by the alcohol supplied and this alcohol is ignited by a spray of diesel oil injection.

ENERGY CONSIDERATION

The calorific value of alcohols is lower than the diesel oils and hence a larger quantity of alcohols has to be used for producing the same amount of power output. However the air requirement for combustion is lower and hence the energy content of the mixture is the same. Since the latent heat of vapourisation is very high, the temperature and pressure at the end of compression come down due to their evaporation. Hence if the alcohol

Injection rate exceeds a limit, the injected diesel will not be able to ignite and hence the engine will fail to function.

EXHAUST GAS RECIRCULATION

NEED FOR EGR

During acceleration and normal running condition, the combustion temperature inside the combustion chamber is around 2000 Fahrenheit. This condition is favorable for the NOx formation. The nitrogen and oxygen in the combustion chamber can chemically combine to form nitrous oxides, which, when combined with hydrocarbons (HCs) produces harmful effects.

EVOLUTION OF EGR :-- General Motors in 1970

PRINCIPLE:-

The exhaust from the combustion chamber is being circulated back to intake manifold by a simple piping mechanism. By this way the fuel charge is diluted and temperature is reduced so as to reduce harmful emission.

The amount of exhaust circulated is determined by the Electronic control unit (ECU).Depending upon the engine loading condition, the flow is allowed by the EGR valve which is actuated by ECU.

Conditions when EGR should not respond are:

Higher accelerating conditions.

During idling and cold start conditions.

EGR has to work for a normal loading and running condition. This phenomenon is not really understood by the people early and they started to disconnect the EGR system from the Engine. To overcome the above listed problems, closed loop system was invented in the early 1980s. The working of such EGR system is explained below.

THE DESIGN CHALLENGE

The EGR system of today must precisely control the flow of re-circulated exhaust. Too much flow will retard engine performance and cause a hesitation on acceleration. Too little flow will increase NOx and cause engine ping. A well-designed system will actually increase engine performance and economy. As the combustion chamber temperature is reduced, engine detonation potential is also reduced

It has a diaphragm that pulls open a valve stem, which allows exhaust to enter

the intake manifold when ported vacuum is applied to it. Ported vacuum increases with throttle opening. A thermal vacuum switch prevents vacuum from reaching the EGR during cold engine starts.

Lowering the amount of oxygen in the cylinder and the combustion temperature, NOx emission is reduced therefore at the source of origin. Cooling the recirculate gas enhances the effectiveness of EGR and thus the further reduction in NOx. Intensified EGR cooling serves to reduce NOx and exhaust smoke particularly at peak load.

Increased EGR cooling has practically no effects on NOx and smoke emission at very low loads (1000 rpm, 2 bar), nevertheless this causes increased HC and CO emissions. Therefore, to control these emissions, an EGR cooler by-pass has to be installed. This by-pass serves to conduct partial flow or full flow of the exhaust gas depending on the load and speed. The EGR cooler will also be by-passed for engine cold start and warm-up.

EGR can also be used by using a variable geometry turbocharger (VGT) which uses variable inlet guide vanes to build sufficient back pressure in the exhaust manifold. For EGR to flow a pressure difference is required across the intake and exhaust manifold and this is created by the VGT.

The purpose of the Exhaust Gas Recirculation (EGR) system is to reduce engine exhaust gas emissions in accordance with EPA regulations.

Part of the exhaust gasses from the combustion chamber is routed from the exhaust manifold through the EGR cooler, past control and reed valves, and are mixed with the intake manifold charge air. The addition of cooled exhaust gasses back into the combustion airflow reduces the peak in combustion temperature. Less oxides of nitrogen (NOx) are produced at lower combustion temperatures. The recycled exhaust gasses are cooled before engine consumption in a tube (radiator) and circulated

FLOW DIAGRAM OF EXHAUST GAS IN EGR TECHNOLOGY

COMPONENTS:--

EGR COOLER

The EGR Cooler is equipped with a single-pass cooler. Part of the exhaust gasses from the cylinders are directed through the EGR shutoff valve and through the cooler and reed valves, past the EGR modulated control valve and the mixer and then back to the cylinder.

EGR CONTROL VALVES

The EGR shutoff valve and the EGR modulated control valve are control valves. The EGR shutoff valve is a pneumatically driven butterfly valve, located at the inlet of the EGR cooler. It closes when the exhaust flap or turbo-brake actuates, avoiding exhaust gas flow and excessive pressure in the EGR cooler and reed valves. The EGR modulated control valve is an electronically actuated butterfly valve located after the EGR cooler and reed valves, controlled by the ECU. This valve controls the exhaust gas flow for the intake manifold.

REED VALVES

The reed valves work like a check valve, allowing flow of gas only in one direction, avoiding gas back flow when the intake pressure is higher than exhaust gas pressure. As the average exhaust pressure is lower than the intake pressure, the gas flow through the reed valves is possible due to exhaust gas pressure peaks — peaks slightly higher than the intake air pressure, which occurs as the engine exhaust valves open. During this peak of pressure, the reed valves open and allow gas flow to the EGR modulated valve and mixer.

EGR MIXER

The purpose of the mixer is to ensure good mixing of the cooled EGR gasses with filtered charge air. Once the exhaust gasses are cooled and have completed their cycle through the EGR system, they are released into the EGR mixer. The recycled exhaust gasses are combined with the charged air and directed to the cylinder.

EFFECT ON EMISSIONS AND DRIVEABILITY

Too little EGR flow may cause detonation and emission failure for excessive NOx. Because EGR tends to reduce the volatility of air fuel charge, loss of EGR causes detonation to occur.

Too much EGR flow for driving conditions may cause stumble, flat spot and hesitation. Because EGR dilutes the air fuel charge, too much EGR for a given engine demand can cause a misfire. It is uncommon to see tip in hesitation, stumble and surging when too much EGR is metered.

CONCLUSION

• A good engine needs high efficiency, high performance characteristics, low emission standards. It seems that the above mentioned solution meets all these specified standards.
• For the practical implementation, changes in the design of Compression Ignition engines are not of a greater magnitude. The only change that has to be implemented is that the metering system should be able to meet 9:1 air fuel ratio.
• Further cold starting is performed efficiently using glow plugs. It is very much essential to implement the dual fuel technique ASAP in order to save the ozone layer and to live in a green world.
• Indian economy can be considerably saved because the fuel usage does not involve any foreign exchange.