RICE HUSK GASIFIER STOVE

Abstract

The stove basically is a top-lit updraft type(T-LUD) which follows the principle of gasification converting the raw rice husk into combustible gases resulting the luminous blue flame. With the thermal efficiency of nearly 20%, this gasifier stove can be fabricated using the locally available materials. Since the smoke and tar emission was found to be very minimal, it can be better alternative than the other traditional stove.

Introduction

It is estimated that about 40% of the global population relies on combustion of solid biomass for household energy need. The incomplete combustion process gives out smoke containing carbon monoxide and other harmful gases. Exposure to CO and other harmful gases emitted from incomplete combustion of solid biomass leads to numerous health effect and environment pollution.

Biomass currently covers approximately 10% of the global energy supply. Rice husk is an agricultural bio-waste having high potential for power generation. The gas stoves using rice husk were started from An Giang, province of Vietnam but the feasibility in terms of technology, social economy and environmental benefits were not concerned at that time. Later, Belonio started work relating to rice husks and the gas stove in 2003 at a time when there were high fuel prices. He then modified previously used stove into gasifier stoves. In Asian countries, rice husk is partly used as an energy source for cooking, heating and other purposes. It is estimated that worldwide 38 to 57 million tons of rice husk is available for energy generation.

Energy consumption and utilization pattern in Nepal differs from industrialized country. In Nepal, biomass accounts for approximately 87.1% of the total energy use. According to the census 2011, about two-third of the total households (64%) uses firewood as usual source of fuel for cooking followed by LPG (21.03%), cow dung (10.38%). Nepal have the potential of producing 0.86 million tons of rice husk. So, keeping in view of problems related to availability and price of LPG; throughout the world, energy consciousness has been developed and researchers are widely participated for the utilization of available resources and find the sustainable device with sustainable material (rice husk in context of Nepal). The different types of the gas stoves used in Nepal are: mud stove, metallic stove, wood stove and they have the efficiency less than 20%. But Rice husk gasifier stove is expected to have the efficiency of near about 25%.

Burning of solid biomass in traditional way produces large amount of smoke, this is termed as indoor pollution. Nepal has many households that are suffering from indoor pollutions. The few methods for increasing efficiency using rice husk and reducing indoor pollution may be:

1. The use of improved stoves such as gasifier stove over traditional stoves.

2. The quality of fuel being used can be upgraded by turning them into briquets and drying the solid biomass before burning the fill.

Significance and Scope:

The rice husks gas stove technology was found to have the following advantages, not only to the user but to the public as well:

➢ It is good replacement for LPG stove, in terms of fuel saving and quality of flame (i.e. luminous blue flame) produced during cooking. By direct energy conversion, about 23 tanks of 11-kg LPG fuel can be replaced by a ton of rice husks.

➢ It will significantly reduce the cost of household spending on conventional fuel sources such as electricity, kerosene, wood and wood charcoal.

➢ It will minimize the problem on household disposal which contributes a lot on environmental pollution.

➢ It will help reduce the carbon dioxide emission in air brought about by the excessive burning of wood and other biomass fuel in the traditional cook stoves, which consequently in the “greenhouse effect” into the atmosphere.

➢ It will help to prevent the deforestation to produce wood fuel, minimizing problems related to the environments.

➢ It doesn’t produce smoke and has stable fire without a tar like residue which is not harmful for human health.

Limitations:

1. Difficult to refill rice husk during the operation of gasifier, once the rice husk is finished in the reactor.

2. Difficult to get the required air from secondary holes as per the air supplied from fan.

3. Only applicable for those areas where the rice husk is easily available.

Scenario of Biomass in Nepal

Today major population depends upon non-renewable sources.70% of energy are obtained through firewood. Less than 1% people uses renewable sources. Most of the primary energy (about 70%) represents solid fuels used in the residential sector etc. And about 95% of the biomass is used for cooking and heating purposes. However, its use is inefficient and poses a threat to the country’s forests.

The kinds of Biomass available in Nepal are: -

➢ Wood products: -non-timber, tree removals, sawmill and other wood manufacturing residue dedicated forest

➢ Solid waste: -municipal solid waste, hospital wastes

➢ Landfill gas and Biogas: -methane, fermented gas

➢ Agricultural products: - rice husk, fibers, raw materials

The Types of Biomass Fuels Available in Nepal are: -

➢ Woody fuels: -deadfalls, woody crops, woody wastes

➢ Forestry: -forest debris

➢ Mill Residues: -rice husk, saw-dust

➢ Agricultural Residues: -rice husk, straw

➢ Dedicated Biomass Crops: -willow, maize, millet

➢ Chemical Recovery Fuels: -polymer waste, textiles

➢ Dry Animal Manure: -dry dung

➢ Wet Animal Manure: -dairy manure slurry

Working of Four Stroke cycle Diesel Engine

The working cycle of the engine is completed in four strokes and diesel is used as fuel. In this engine, spark is not used to ignite the charge but high compression itself ignites the fuel mixture. The working of the engine is described below:

a.       Suction stroke

The suction stroke is similar to that of petrol engine except that only air is taken into the cylinder during this stroke.

b.      Compression stroke

Compression stroke is also similar to that of petrol engine, but at the end of compression stroke, pressure and temperature of air reaches about 60 bar and 600⁰c respectively.

c.       Expansion stroke

During this stroke, both inlet and exhaust valve is kept closed and fuel valve opens just before the beginning of the third stroke. The supply of fuel is continued during a small part of expansion stroke. The temperature of the air at the end of compression stroke is high enough to ignite the fuel (Diesel). The combustion of fuel is continued at the constant pressure (isobaric process) as long as the fuel valve is open. The high pressurized gases pushes the piston downward even the fuel valve is closed.

d.      Exhaust stroke

During exhaust stroke, inlet and fuel valve remains closed and exhaust valve opens. The upward movement of piston pushes the burned gases outside the cylinder body. When piston reaches TDC, exhaust stroke is completed and becomes ready for next cycle.

Working of Four Stroke Cycle Petrol Engine

Basic Engine nomenclature

Engine parts have been described in previous blog (Link is provided at the bottom of this blog). Some standard terminology commonly used for IC engine is described below:

a.       Bore

The inside diameter of the cylinder is known as bore.

b.      Stroke

The maximum distance travelled by the piston inside the cylinder in one direction is known as Stroke. It is equal to the twice the radius of crank.

c.       Top Dead Center (TDC)

The extreme position of the piston at the top of the cylinder (head end side) is known as top dead center. In case of horizontal engines, it is known as Inner Dead Center (IDC) position.

d.      Bottom Dead Center (BDC)

The extreme position of the piston at the bottom of the cylinder is called bottom dead center and in case of horizontal engines, it is known as Outer Dead Center (ODC) position.

e.       Stroke length

The distance between TDC and BDC is known as stroke length.

f.       Clearance volume

The volume contained in the cylinder above the top of the piston when the piston is at TDC, is called clearance volume.

g.      Piston displacement or Swept Volume

The total volume swept by the piston in moving between TDC and BDC is known as piston displacement or swept volume.

So cylinder volume is the sum of clearance volume and piston displacement volume.

h.      Compression ratio

The ratio of volume when the piston is at BDC to the volume when the piston is at TDC is known as compression ratio.

Numerically,

Compression ratio (Rc) =  cylinder volume / clearance volume

  

Working of Four stroke cycle petrol Engine:

The working cycle of the engine is said to be completed when it complete four strokes or two revolutions of crank and petrol is used as fuel.

Fig: Working of Four stroke petrol engine

Four strokes are described below:

a.       Suction stroke

The downward movement of piston from TDC to BDC is known as Suction stroke and the crank rotates by 180⁰ during this period. In this stroke, the piston is at the top most position (TDC) and is ready to move down drawing the air fuel (petrol) mixture. The inlet valve is open and the exhaust valve is closed during this stroke. As the piston moves downward, a fresh charge of air fuel mixture enters the cylinder through the inlet valve due to the suction created and is continued until the piston reaches BDC. At this position, inlet valve closes and steps towards next stroke.

b.      Compression stroke

During this stroke, both inlet and exhaust valve is closed and piston moves upward and compresses the charge enclosed in the cylinder. During this process, the pressure and temperature of the mixture increases rapidly. As the piston reaches the top dead center, the mixture is ignited with the help of spark generated by spark plug(s). The burning of the mixture is more or less instantaneous and the pressure and the temperature of gases increases at the constant volume (isochoric process).

c.       Power stroke or Expansion stroke

During this stroke, work is done. The increase pressure of gases exerts a large amount of force and pushes the piston down. During the expansion stroke, both valves remains closed. Piston moves from TDC to BDC reducing high temperature and high pressure gradually. The exhaust valve opens as the piston reaches BDC position and pressure falls suddenly to the atmospheric pressure at constant volume.

d.      Exhaust stroke

During the upward motion of piston, the exhaust valve is open and inlet valve remains closed. The upward movement of piston pushes the burnt gases outside the cylinder through exhaust valve. As the piston reaches TDC, again inlet valve opens and fresh charge is taken inside and the cycle repeats.

https://mechanicaengg.blogspot.com/2019/01/internal-combustion-ic-engine-and-its-components-piston-cylinder-crankshaft-cam-camshaft-inlet-exhaust-rocker-arm-flywheel-governor-carburetor-spark-plug-fuel-nozzle-wristpin-bearing-manifold.html

Anti-Lock Braking System (ABS)

Introduction

Assume that you are driving on a moderately busy highway in rain. You are in your own lane travelling at safe speed. Suddenly a car overtakes with a sharp turn and you steps on the brake paddle. What would happen next? There is chances of sliding and crashing into other lanes with other vehicles. You might lose control once your steering wheel is locked.

Such conditions might get worse and cause great losses of vehicles and in worst case even death.

To prevent this many attempts were made and in mid 1980s ABS was introduced that bring many changes and prevents from many accidents in such possible events.

ABS stands for Anti-lock Braking System. It was designed to help the driver maintain better steering control and avoid skidding while braking. Modern automobile is equipped with advanced ABS. This promotes directional stability and allows steering while maximizing braking by reducing stoppage distance. ABS allows driver to maintain control of vehicle. Since ABS allows driver to steer the vehicle and still maintain braking.  ABS operates by preventing the wheels from locking up during uncontrolled braking, thereby maintaining tractive contact with the road surface. On slippery surfaces, professional driver cannot stop the vehicle as quickly at safe distance without ABS as an average driver can with ABS. ABS operates at a very much faster rate and more effectively than most drivers could manage. On varieties of its application and capabilities, it is also known variously as Electronic Brake Force Distribution (EBD), Traction control system, emergency brake assist or electronic stability control (ESC).

Working Principle

It is simple to understand the working principle of ABS. A skidding wheel has less traction force than a non skidding wheel. If driver is stuck on a slippery surface like in rain or on ice, driver should that if the wheels are spinning then it has no traction. This is because the contact patch is sliding relative to the surface. ABS modifies the brake fluid pressure, independent of the amount of pressure being applied on the brakes, to bring the speed of the wheel back to the minimum slip level that is mandatory for optimal braking performance.

Components of ABS

ABS has four major components:

a.       Speed Sensor

The speed sensor uses a magnet and a Hall effect sensor or a toothed wheel and an electromagnetic coil to generate a signal. The speed sensors, which are located at each wheel, or in some cases in the differential,  provide the information to ABS when a wheel is about to lock up. This sensor monitors the speed of each wheel and determines the necessary acceleration and deceleration of the wheels.

b.      Valves

There is a valve in the brake line of each brake controlled by the ABS. The valve regulates the air pressure to the brakes when ABS is active. On some systems, the valve has three positions:

Ø  In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.

Ø  In second position; the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.

Ø  In third position; the valve releases some of the pressure from the brake.

c.       Electronic Control Unit (ECU)

ECU serves as the brain of ABS. It is an electronic control unit that receives, amplifies and filters the sensor signals for calculating the wheel rotational speed, acceleration or deceleration. It consists of pre-programmed advance algorithms which controls the brake pressure according to the data analyzed by the unit.

d.      Pump

When valve releases pressure from the brakes, for periodic use, pump put that pressure back. Pump restore the pressure to the hydraulic brakes after the valve have releases it. Pump is automatically controlled by ECU. When driver releases pedal, pressure is restored automatically with the help of pump.

Internal Combustion (IC) Engine and its Components

In previous blog, we have discussed about IC engine and before jumping to this blog, readers are requested to visit the link given below:
IC Engine

Engine or motor is a device designed to convert one form of energy into mechanical energy. The arrangement of different parts of four stroke spark ignition engine (Petrol engine) and four stroke compression ignition engine (Diesel engine) is shown in the figure below:

                                          Figure: Four Stroke Petrol Engine

                                        Figure: Outline of Diesel Petrol Engine

The purpose of each part is described in short:

1.      Cylinder

The cylinder of IC engine is considered as main body of engine in which piston reciprocates to develop power. It has to withstand very high pressure of about 70 bar and temperature of about 2200^o C because there is direct continuous combustion inside the cylinder. So its material should retain strength at high temperatures without any deformation, should be good conductor of heat and should be able to resist to wear and tear due to reciprocating parts. Generally, ordinary cast iron is used but incase of heavy duty engines, alloy steels are used.

2.      Cylinder head

The cylinder seals one end of the cylinder. It houses the inlet, spark plug and exhaust valve through which the mixture of air and fuel is taken and burnt with the help of spark produced by spark plug and burnt gases are exhausted to the atmosphere from exhaust. A copper and asbestos gaskets are provided between the cylinder and cylinder heat to obtain a gas tight joint.

3.      Piston and piston rings

The primary function of piston is to compress the air fuel mixture during compression stroke and to transmit the gas force to the connecting rod and then to the crank during power stroke. Generally, the piston of IC engine are made up of cast iron, cast steel and aluminium alloy. Often piston is considered as heart of the engine.

The piston rings are placed in the circumferential grooves provided on the outer surface of the piston. It gives gastight fitting between piston and cylinder and prevents from the leakage of high pressurized gases. It is made from special grade cast iron which can retains its elastic property at very high temperatures. The upper piston rings are called compression rings and lower piston rings are called the oiling or oil control rings.

4.      Connecting rod

Connecting rod joins piston with crank. It is usually a steel forging of circular, rectangular, I, T, or H section and is highly polished for increased endurance strength. Its small ends forms a hinge and pin joint with piston and its big end is connected to the crank by crank pin. It has a passage for the transfer of lubricants from the big end bearing to small end bearing also known as gudgeon pin.

5.      Crank and crankshaft

The crankshaft is the backbone of the engine. The main function of crankshaft is to take power produced by engine and transmit it to the output shaft. Both crank and crankshafts are steel forged and machined to a smooth finish. Both are held together with the help of key. Crankshaft is supported in the main bearings held by engine block and has a heavy wheel, known as flywheel, to even out the fluctuations of torque. The power required for any useful purpose is taken out from crankshafts only.

6.      Piston pin or Wrist pin

The piston pin provides the bearing for the oscillating small end of the connecting rod.

7.      Inlet valve

This valve is responsible for the injection of air fuel mixture into the cylinder during suction stroke of the engine. It is controlled by cam shaft mounted on top of it.

8.      Exhaust valve

This valve is responsible for the removable of burnt gases from the cylinder after the power stroke. It is also controlled by cam shaft mounted on top of it.

9.      Valve spring

It is used to keep valves closer to each other.

10.  Inlet manifold

It is the path from where air fuel mixture is carried from carburetor to the petrol engine.

11.  Exhaust manifold

It is the passage from which carries the exhaust gases from exhaust valve to the atmosphere.

12.  Cam shaft

The function of cam shaft is to control the motion of intake and exhaust valves through the cams, cams follower, push rods and rocker arm. The cam shaft is driven positively from the crankshaft and is connected with timing chain.

13.  Cam and cam follower

It is made of a required profile to give desired motion to the valves through the followers.

14.  Push rod and rocker arm

Push rod and rocker arm transmits the motion of cam to the valves. These links together are also called valve gear.

15.  Crank case

It is the base which holds the cylinder and the crankshaft. It also serves as the sump for lubricating oil.

16.  Water jacket

It serves as cooling device for the engine operating at high temperatures.

17.  Bed plate

The lower portion of the crank case is also known as the bed plate. For concrete foundations, bed plates are hold the bed bolts.

18.  Flywheel

It is the wheel mounted on the crankshaft which stores the excess energy during the power stroke and returns the energy into the other strokes and maintains a fairly consant output torque on the crankshafts.

19.  Governor

The function of the governor is to regulate the air fuel mixture in case of petrol engine and amount of fuel in case of diesel engine to maintain a constant speed of the engine. It is run by a drive from the crankshaft.

20.  Carburetor

The function of carburetor is to supply the uniform mixture is air and fuel to the cylinder of petrol engine through the intake manifold. The mass of mixture entering the cylinder is controlled by the throttle valve.

21.  Spark plug

The function of spark plug is to ignite the air fuel mixture after completing the compression in the petrol engine. It is generally mounted on the cylinder head. This is not used in diesel engine.

22.  Fuel pump

It forces the fuel at high pressure through the fuel nozzle into the cylinder at the end of compression stroke in diesel engine.

23.  Fuel nozzle

The function of fuel nozzle is to break up the liquid fuel into a fine spray as it enters the cylinder for proper combustion. It is used in diesel engine.

YV Nitesh

13^th Jan 2019

Internal Combustion Engine

Heat Engine

An Engine is defined as a mechanical device which converts one form of energy into mechanical energy. The transformation of one form of energy into another required form is always associated with losses, therefore, the efficiency conversion plays an important role. Heat is considered as poor form of energy where mechanical work is considered rich form of energy as its back conversion with very high efficiency (90-95%) is possible. In every heat engine, some form of fuel (solid, liquid, gas or nuclear) is used. The chemical or nuclear energy of fuel is converted into thermal energy and that is further converted into mechanical energy to perform some useful work.

The heat engines are classified as;     

a.       External Combustion Engines,

b.      Internal Combustion Engines (IC Engine)

An External Combustion Engine is a thermal power plant as shown in the figure where fuel is burned and its heat is given to the water to generate steam which further used for power generation. The working fluid is not mixed with fuel, therefore, the same working fluid (water) is used again and again in the system. Trains in development phase used external combustion engine and they were also called as Steam Engine.

The Internal Combustion Engine is a gas turbine plant as shown in figure below where fuel is mixed with air and burned. The hot gasses are passed through the turbines to generate power and then the gases are exhausted through exhaust valve. In this case same working fluid cannot be used over again and again in the repeated cycle. During next cycle, again, the fresh air is taken and mixed with fuel for next power stroke.

In above described internal combustion system, compression, combustion and expansion are carried out in different components. But in conventional IC engines, all the above mentioned processes (suction, compression, ignition and exhaust) are carried out inside cylinder and piston only. The simple arrangement is shown below:

Development of IC Engine:

1.      Hugens’ Gunpowder Engine:

The first IC engine was developed in the year 1680 by Dutch physicist Hugens using gunpowder as fuel. It consists of cylinder and piston and has arrangement as shown in the figure below:

The upward stroke of the piston was caused by the explosion of gun powder and the return stroke was caused by the atmospheric pressure acting on the other side of the piston and arising from the pressure drop in the cylinder as the gasses starts to cool. The engine worked with a single explosion charge and he was unable to produce sequential explosion necessary for continuous operation.

2.      The Lenoir Engine:

In 1860, Lenoir developed non-compression type gas engine using coal gas as fuel. This engine was similar to double acting steam engine except a mixture of gas and air was used as working fluid instead of steam. The efficiency of this engine was considerably low because of low expansion ratio.

The charge of gas and air was induced during part of the suction stroke and then it was ignited by an electric spark. The combustion of gas caused rise in pressure and temperature of mixture and did work on the piston during remaining part of the stroke. The gases after expansion were discharged to the atmosphere during return stroke. The P-V diagram fir Lenoir Engine is shown below:

3.      Otto-Langen Free Piston Engine:

Developed in 1866, it also consists of piston and cylinder arrangement but piston was not connected to any crankshaft and was free to move vertically outward during expansion stroke. As the explosion of gas and air takes place, the pressure and temperature of the mixture increases and piston is pushed upward. After expansion stroke, mixture is cooled and piston comes down with gravity causing downward stroke. The piston rod is connected to the flywheel by a ratchet and rack and pinion device. During downward stroke, the piston opens the sliding type exhaust valve and allows the burnt gases to go to atmosphere. The contact between the flame and mixture in the cylinder was provided with the help of an eccentric driven valve. The arrangement of engine is shown in the figure below:

4.      Four-stroke Otto-Engine

Otto developed a four stroke engine commonly known as suction, compression, power and exhaust. He used gas as a fuel and compression ratio was hardly 3. All the spark ignition (SI) engines operates on the same principle of Otto-cycle gas engine. The development of Otto engine is considered as an epoch making event in the history of IC engines. The development of this engine founded the IC engine technology and is still used today as a base for design.

5.      Brayton Engine

It is constant pressure combustion and complete expansion engine. It has two cylinders, one is used to compress the air and other is used to expand the high pressure, high temperature gases upto atmospheric pressure.

When the oil is used as fuel, the fuel is injected in the high pressure air coming from the compressor and heated higher pressure gases are expanded in the expansion cylinder known as engine. An ignition flame was supported mixture bypass and flame suppression grid prevented the flame from flashing back into receiver.

The arrangement of this engine is shown in figure:

6.      Atkinson Engine

It uses a short stroke for suction and compression and a long stroke for expansion and exhaust as shown in figure on P-V diagram. Atkinson used a single cylinder, as against two cylinders in Brayton engine. But the linkage mechanism was very complicated and because of that mechanical efficiency was considerably low. A constant volume gas turbine was also operated on this cycle which has become presently obsolete.

7.      Diesel Engine

It was developed in 1892 by Rudolf Diesel. He purposed to inject the liquid fuel in a compressed air at the end of compression. The temperature of compressed air was sufficient to burn the injected fuel. Therefore, these engines are commonly known as Compression Ignition (CI) engines. Two stroke and four stroke with airless injection are commonly used in different fields.

Classification of IC Engines

The internal combustion engines are usually classified on the basis of cylinder arrangement, cycle of operation, type of fuel used, method of charging the engine cylinder, type of ignition and type of cooling.

a.       Classification as per cylinder arrangement

·         Inline engine

·         V-type engine

·         Radial engine

·         Opposed piston engine

·         Opposed cylinder engine

·         Delta type

b.      Classification as per number of strokes

·         Two stroke

·         Four stroke

c.       Classification as per the type of fuel uses

·         Petrol engine

·         Diesel engine

d.      Classification as per the cooling system used

·         Air cooled engines

·         Water cooled engines

e.       Classification as per the thermodynamic cycle used

·         Otto cycle

·         Diesel cycle

·         Dual cycle

·         Brayton cycle

YV Nitesh

12^th Jan 2019