Thermodynamics Flashcards

Question

Diesel Engine cycle

Answer 1

COMPRESSION during suction stroke, air, instead of a fuel-air mixture higher compression ratios employed, the temp at the end of the compression stroke is sufficiently high to self ignite the fuel which is injected into the combustion chamber. In CI engines, a high pressure fuel pump and an injector are provided to inject the fuel into the combustion chamber. SUCTION STROKE Air alone is inducted Air is compressed into the clearance volume. Both valves remain closed EXPANSION Fuel injection starts nearly at the end of the compression stroke. The rate of injection is such that combustion maintains the pressure constant in spite of the piston movement on its expansion stroke increasing the volume Heat is assumed to have been added at constant pressure. After the injection of fuel is completed (i.e. after cut-off) the products of combustion expand. Both the valves remain closed during the expansion stroke. EXHAUST The piston travelling from BDC to TDC pushes out the products of combustion. The exhaust valve is open and the intake valve is closed during this stroke

Answer 2

IP: The power developed inside the cylinder of the engine BP: It is the net power available at the crank shaft of the engine for performing useful work (BP). It is always less than indicated power since a part of the power developed in the engine cylinder is used to overcome the frictional losses at different moving parts of the engine. The arrangement is known as dynamometer. Usually, rope brake dynamometer a device designed to assess the power of an engine shaft by introducing frictional resistance to the shaft's motion through the use of a rope 2𝜋𝑁𝑇/60×1000 (kW) N=Crank Speed, TORQUE = 𝑇 = (𝑊 − 𝑆) ×(𝐷𝑏+𝑑𝑟)/2 W= weight, S=spring balance Db=diameter of brake drum, dr=diameter of rope

Answer 3

FP = IP – BP mech = BP/IP Nith = 𝐼𝑃/(𝐶𝑉 × 𝑚f) Nbp = 𝐵𝑃/(𝐶𝑉 × 𝑚𝑓)× 100 CV is the calorific value of the fuel in KJ/kg mf is mass flow rate of the fuel in kg/s. units are in kW Specific fuel consumption ISFC =𝑴𝒂𝒔𝒔 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒊𝒏 (𝒌𝒈/𝒉𝒓)/𝑰𝒏𝒅𝒊𝒄𝒂𝒕𝒆𝒅 𝑷𝒐𝒘𝒆𝒓 𝒊𝒏 𝒌𝑾 BSFC = 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒇𝒖𝒆𝒍 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒊𝒏 (𝒌𝒈/𝒉𝒓) /𝑩𝒓𝒂𝒌𝒆 𝑷𝒐𝒘𝒆𝒓 𝒊𝒏 𝒌W both mf should be divided by 3600 as it should be per second Specific fuel consumption – It is the mass of fuel consumed per kW of power developed per hour and is a criterion of economical power production Mf= fuel flow(L)*1000*specific gravity fuel flow in default will be in m^3 and should be per/sec Kg/s => L/s divide mf/specific gravity litres should be converted m^3 divided 1000

Answer 4

petrol are lighter engines than diesel, and the are higher speed(rpms) than diesel, diesel has higher compression ratios thus greater thermal efficiency PERFORMANCE OF ENGINE diesel engines are heavier due to higher peak pressures compared to petrol engines Maximum power or torque Specific fuel consumption Reliability and durability By using experimental results obtained from engine tests. By analytical calculation based on theoretical data By doing numerical caluculation using theoretical data

Answer 5

MOTOR high torque electric motor. While braking, it acts like a generator (regenerative braking) and recharges the batteries. BATTERY TYPES Those are lead acid batteries, nickel metal hydride (NiMH) batteries and lithium ion (Li – ion) batteries. CONTROLLER a computerized motor controller. regulates the flow of energy from the power pack to the motor in relation to the pressure applied on the accelerator DC/DC CONVERTER A 12V auxiliary battery in an electric car to power all 12V accessories such as lights, horn etc. by cutting battery pack voltage down to 12V EMS The brain of EVs that monitors and controls all required functions. It is a computer based system that optimizes charging and energy output of batteries to maximize operating range and improve performance.

Answer 6

In case of series hybrid system, the mechanical output(IC engine) is first converted into electricity using a generator. The converted electricity either charges the battery or can bypass the battery to propel the wheels via the motor and mechanical transmission.

Answer 7

The parallel HEV allows both IC engine and electric motor to deliver power to drive the wheels since both IC engine and electic motor aee connected to the shaft via two clutches, the propulsion power may be delivered by IC engine alone, by electric motor alons, or both IC engine and electric motor. The electric motor can be used as a generator by absorbing the battery by regenerative braking or by absorbing power from the IC engine when its output is greater than required for the output for the wheels

Answer 8

In the series-parallel hybrid, the configuration incorporates the features of both the series and parallel HEVs. However, this configuration needs an additional electric machine and a planetary gear unit making the control complex. ADV:This setup takes advantage of the strengths of both configurations to maximize efficiency, flexibility, and performance under different driving conditions. City driving (low speeds): At low speeds or in stop-and-go traffic, a series hybrid mode is more efficient. At higher speeds, the parallel hybrid mode is more efficient.

Answer 9

They have two complementary drive systems: an IC engine with a fuel tank and an electric motor with a battery. HEVs cannot be recharged from the electricity grid – all their energy comes from fuel and from regenerative braking. difference between series and parallel hybrid: parallel mode is used when both the electric motor and internal combustion engine (ICE) can provide power simultaneously, while series mode is used when the electric motor is the only source of mechanical power

Answer 10

ferrous and nonferrous Ferrous alloys, those in which iron is the principal constituent, include steels and cast irons ex: STEEL iron-carbon(less than 2 percent) The nonferrous ones—all alloys that are not iron based. alloy steel Steels which acquire some characteristic properties due to the addition of alloying elements other than Carbon; for specific properties

Answer 11

0.25% Carbon Relatively soft and weak Outstanding Ductility and Toughness Very good Machinability and Weldability eg. Mild Steel Least expensive to produce Unresponsive to hardening heat treatment Very low hardenability Automobile body components Structural shapes (I beams, Angle Irons); Sheets used in tin cans, buildings etc. medium carbon steel 0.25% to 0.6 carbon Stronger than Low Carbon Steels Less tougher Best range for adding alloying elements Good mix of ductility and strength Railway wheels and tracks Gears Crankshafts and other machine parts High carbon steels From 0.6% to 1.4% carbon Hardest Strongest Least ductile when compared with Low Carbon and Medium Carbon Steel Best range to make tool steels Cannot be used for operations where ductility and malleability are required Knives ; Razors ; Hacksaw blades ; High strength Wires

Answer 12

alloys having carbon content above 2.1% by weight, most cast irons contain carbon between 3 – 4.5% by weight and in addition Cast Irons are also very brittle. Therefore, casting is the most convenient fabrication technique. 1) Gray Cast Iron 2) Nodular or Ductile Cast Iron 3) White Cast Iron 4) Malleable Cast Iron DIS ADVANTAGES a relatively high density, a comparatively low electrical conductivity, and an inherent susceptibility to corrosion in some common environments.

Answer 13

2.5% to 4% Carbon 1% to 3% Silicon Weak and brittle in tension Higher Compressive strength effective in damping vibrations High resistance to wear High fluidity at molten state (This permits casting pieces to have intricate shapes) Low Cost Automotive Engine Blocks Brake discs and drums Base structure of machines and heavy equipments that are exposed to vibrations etc. DUCTILE OR NODULAR CAST IRON 3% to 4% Carbon 1.6% to 2.8% Silicon Highly ductile Very good machinability High Corrosion Resistance Valves Pump bodies Crankshafts Gears and other automotive and machine components etc WHITE CAST IRON 1.8% to 3.2% Carbon 0.3% to 1.8% Silicon Very hard and brittle Highly wear resistant No Ductility and Malleability Not Machinable Liners for Cement Mixers Ball Mill Certain types of Drawing Dies Extrusion Nozzles etc. 1.8% to 3.2% Carbon 0.3% to 1.8% Silicon MALLEABLE CAST IRON Highly Malleable Very good Machinability Good Magnetic properties Wear Resistance Connecting Rods Transmission Gears Flanges Pipe Fittings Differential Cases for Automobiles etc.

Answer 14

Copper has - good thermal and electrical conductivity ease of getting cast, machined and brazed - good corrosion resistance Pure copper is mainly used for electrical and thermal applications. ALUMNIUM Low specific gravity, Corrosion resistance , Ease of fabrication, High electrical and thermal conductivity, Aircraft structural parts and other highly stressed applications, Flywheel etc. MAGNESIUM ALLOYS for light weight alloys is relatively soft, and has a low elastic modulus APPLICATIONS: variety of hand-held devices (e.g., chain saws, power tools, hedge clippers), TITANIUM has a relatively low density a high melting point and an high elastic modulus TITANIUM extremely strong; tensile strengths are high the alloys are highly ductile and easily forged and machined. -airplane structures, space vehicles, surgical implants, ,petroleum and chemical industries.

Answer 15

metallic and non – metallic elements with predominantly ‘ionic’ interatomic bonding. turbocharger rotors, aerospace turbine blades, nuclear fuel rods,

Answer 16

Plastics are synthetic materials processed by heat and pressure. a solid material consisting of an organic polymer of a long molecular chain and high molecular weight THERMOPLASTIC a polymeric material which softens when heated and hardens upon cooling. THERMOSETTING: a polymeric material, which once having cured or hardened by a chemical reaction does not soften or melt upon subsequent heating. A thermoplastic material has a linear polymer chain while a thermosetting plastic material consists of a cross – linked polymer chain as shown. THERMOSETTING VS THERMOPLASTIC The difference in properties of thermoplastic and thermosetting plastic materials is due to molecular structures of their polymer chains.

Answer 17

A composite is a structural material that consists of two or more combined constituents that are combined at a macroscopic level and are not soluble in each other. One constituent is called the reinforcing phase and the one in which it is embedded is called the matrix. The reinforcing phase material may be in the form of fibers, particles, or flakes. The matrix phase materials are generally continuous. Examples of composite systems include concrete reinforced with steel and epoxy reinforced with graphite fibers, etc

Answer 18

the ability of the material to regain its shape and size when the externa forces are removed/when deformation occurs PLASTICITY ability of material to not to take its shape and size when the external forces are removed DUCTILITY ability of the material to be drawn into thin wires when the materials are subjected to tensile MALLEABILITY ability of material to deform into sheets under compression load BRITTLENESS ability of material (% elongation is less than 5%) than its brittle material % elongation (change in L/l)*100 FATIGUE ability of the material to resist deformation due to cyclic loading CREEP it is the function of time and temperature elongated wrt to time changing shape over time HARDNESS ability of the material to resist surface indentation/resistance to penetration = hardness BHN= brinal hardness number VHN=Vekers hardness number RHN=Rockwells Hardness number IMPACT STRENGHT ability of a material to resist the deformation due to sudden load (high magnitude in fraction of time) charpy test rig static: magnitude of load doesnt vary with time, cyclic load varies RESILIENCE V TOUGHNESS (i) Resilience is the ability of the material to absorb energy within elastic limit and release it, whereas toughness is the ability of the material to absorb energy within elastic and plastic range, before fracture. Resilience is essential in spring applications where toughness is required for components subjected to bending, twisting, stretching and impact loads. STIFNESS the resistance of materials to elastic deformation or deflection its called rigidity, how much a material resists deformation in response to an applied force. A material with high stiffness will undergo only slight deformation under load

Answer 19

Smart materials are materials that have to respond to stimuli and environmental changes and to activate their functions according to these changes ELEMENTS OF SMART MATERIALS: Smart materials are thought of as those which produce electric voltages when strained ex: Lead Zirconate Titanate, polyvinylidene fluoride Sensor Actuator Control System Power and Signal Conditioning Electronics Computer

Answer 20

By applying mechanical deformations to these crystals, electric dipoles are generated/pd develops vice versa in certain class of anisotropic Voltage and power sources, sensors

Answer 21

The recovery of strains imparted to the material at a lower temperature, as a result of heating, alloys shape is fixed/memorised at low temp ex: braces, stents One way: after heating deformation are recovered and cooling = back to same shape two way: remembers shape at both high temp and low temp ,thus can be cycled btw these 2 shapes without the need of external stress

Answer 22

A special class of fluids exists that change their rheological properties on the application of an electric or a magnetic field. MAGNETOSTRICTIVE materials that change their shape or dimensions in response to an applied magnetic field

Answer 23

normal stress (perpendicular): tensile,compression , sheer load(parallel)

Answer 24

When the material is compressed, it bulges outward on the sides and becomes barrel shaped, because friction between the specimen and the end plates prevents lateral expansion. With increasing load, the specimen is flattened out and offers greatly increased resistance to further shortening Brittle materials loaded in compression typically have an initial linear region the ultimate stresses in compression are much higher than those in tension. brittle materials actually break at the maximum load unlike ductile draw graph

Answer 25

ISOTHERMAL PV=const, P1V1=P2V2 pdV W=P1V1ln(V2/V1) ADIABATIC PV^a=const, P1V1^a=P2V2^a pdV W=(P1V1-P2V2)/a-1 POLYTROPIC PV^n=const, P1V1^n=P2V2^n pdV W=(P1V1-P2V2)/n-1 ISOCHORIC V=const, dV=0, P1/P2 =T1/T2(Kelvin) pdV W=0 ISOBARIC P=const, dP=0, V1/T1=V2/T2 W=P(V2-V1)