Internal combustion engines ppt

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Reciprocating Internal Combustion Engines Prof. Rolf D. Reitz Engine Research Center University of Wisconsin-Madison 2014 Princeton-CEFRC Summer School on Combustion Course Length: 15 hrs (Mon.- Fri., June 23 – 27, 2014) Copyright ©2014 by Rolf D. Reitz. This material is not to be sold, reproduced or distributed without prior written permission of the owner, Rolf D. Reitz. 1 CEFRC1-1, 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Short course outine: Engine fundamentals and performance metrics, computer modeling supported by in-depth understanding of fundamental engine processes and detailed experiments in engine design optimization. Day 1 (Engine fundamentals) Part 1: IC Engine Review, 0, 1 and 3-D modeling Part 2: Turbochargers, Engine Performance Metrics Day 2 (Combustion Modeling) Part 3: Chemical Kinetics, HCCI & SI Combustion Part 4: Heat transfer, NOx and Soot Emissions Day 3 (Spray Modeling) Part 5: Atomization, Drop Breakup/Coalescence Part 6: Drop Drag/Wall Impinge/Vaporization/Sprays Day 4 (Engine Optimization) Part 7: Diesel combustion and SI knock modeling Part 8: Optimization and Low Temperature Combustion Day 5 (Applications and the Future) Part 9: Fuels, After-treatment and Controls Part 10: Vehicle Applications, Future of IC Engines 2 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Motivation Society relies on IC engines for transportation, commerce and power generation: utility devices (e.g., pumps, mowers, chain-saws, portable generators, etc.), earth-moving equipment, tractors, propeller aircraft, ocean liners and ships, personal watercraft and motorcycles ICEs power the 600 million passenger cars and other vehicles on our roads today. 250 million vehicles (cars, buses, and trucks) were registered in 2008 in US alone. 50 million cars were made world-wide in 2009, compared to 40 million in 2000. China became the world’s largest car market in 2011. A third of all cars are produced in the European Union, 50% are powered diesels.  IC engine research spans both gasoline and diesel powerplants. Fuel Consumption 70% of the roughly 86 million barrels of crude oil consumed daily world-wide is used in IC engines for transportation. 10 million barrels of oil are used per day in the US in cars and light-duty trucks 4 million barrels per day are used in heavy-duty diesel engines, - total oil usage of 2.5 gallons per day per person. Of this, 62% is imported (at 80/barrel - costs US economy 1 billion/day). 3 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling US energy flow chart 18 World energy use = 500 x 10 J 14EJ 23EJ 23EJ 70% of liquid fuel used for transportation 28% of total 40EJ US energy consumption http://www.eia.gov/totalenergy/ 18 100x10 J 4 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Fuel consumption - CO emissions 2 World oil use: 86 million bbl/day = 3.6 billion gal/day (0.6 gal/person/day) Why do we use fossil fuels (86% of US energy supply)? Large amount of energy is tied up in chemical bonds. Consider stoichiometric balance for gasoline (octane) in air: 6 C H + 12.5(O +3.76N )  8CO + 9H O+47N (+ 48x10 J/kg ) 8 18 2 2 2 2 2 fuel Kinetic energy of 1,000 kg automobile traveling at 60 mph (27 m/s) 2 2 2 6 = 1/2·1,000·27 (m kg/s =Nm) 0.46x10 J = energy in 10g gasoline 1/3 oz (teaspoon) Assume: 1 billion vehicles/engines, each burns 2.5 gal/day (1 gal 6.5lb 3kg) 9 6 18  7.5x10 kg /day48x10 J/kg=360x10 J/yr fuel 1 kg gasoline makes 8·44/114=3.1 kg CO 2 9 9 9 365 · 7.5x10 kg /yr 8,486x10 kg-CO /year 8.5x10 tonne-CO /year fuel 2 2 9 (Humans exhale 1 kg-CO /day = 6x10 kg-CO /year) 2 2 18 Total mass of air in the earth’s atmosphere 5x10 kg So, CO mass from engines/year added to earth’s atmosphere 2 12 18 8.5x10 / 5x10 1.7 ppm 5 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling 1% (Prof. John Heywood, MIT) Modern gasoline IC engine vehicle converts about 16% of the chemical energy in gasoline to useful work. The average light-duty vehicle weighs 4,100 lbs. The average occupancy of a light-duty vehicle is 1.6 persons. If the average occupant weighs 160 lbs, 0.16x((1.6x160)/4100) = 0.01 6 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Pollutant Emissions 37 billion tons of CO (6 tons each for each person in the world) from fossil fuels/yr, 2 plus other emissions, including nitric oxides (NOx) and particulates (soot). CO contributes to Green House Gases (GHG), implicated in climate change 2 - drastic reductions in fuel usage required to make appreciable changes in GHG CO emissions linked to fuel efficiency: 2 - automotive diesel engine is 20 to 40% more efficient than SI engine. But, diesels have higher NOx and soot. - serious environmental and health implications, - governments are imposing stringent vehicle emissions regulations. - diesel manufacturers use Selective Catalytic Reduction (SCR) after-treatment for NOx reduction: requires reducing agent (urea - carbamide) at rate (and cost) of about 1% of fuel flow rate for every 1 g/kWh of NOx reduction. Soot controlled with Diesel Particulate Filters (DPF), - requires periodic regeneration by richening fuel-air mixture to increase exhaust temperature to burn off the accumulated soot - imposes about 3% additional fuel penalty. Need for emissions control removes some of advantages of the diesel engine 7 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Goal of IC engine: Convert energy contained in a fuel into useful work, as efficiently and cost- effectively as possible. Identify energy conversion thermodynamics that governs reciprocating engines. Describe hardware and operating cycles used in practical IC engines. Discuss approaches used in developing combustion and fuel/air handling systems. Internal Combustion Engine development requires control to: introduce fuel and oxygen, initiate and control combustion, exhaust products IC engine Heat (EC) engine (Not constrained by (Carnot cycle) Energy release occurs Internal Carnot cycle) Energy release to the system. occurs External Working fluid Heat source Oxygen to the system. undergoes state (P,T) and chemical Working fluid undergoes changes Work Work reversible state during a cycle changes (P,T) Heat sink Fuel Combustion products during a cycle (e.g., Rankine cycle) 8 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Components of piston engine Piston moves between Top Dead Center (TDC) and Bottom Dead Center (BDC). Compression Ratio = CR = ratio of BDC/TDC volumes Stroke = S = travel distance from BDC to TDC Bore = B = cylinder diameter D = Displacement = (BDC-TDC) volume. cylinders 2 = p B S/4 . cylinders Basic Equations P = W.N = T.N P kW = T Nm.N rpm.1.047 E-04 BMEP = P.(rev/cyc) / D.N BMEP kPa = P kW.(2 for 4-stroke) E03 / D l. N rev/s . BSFC = m / P fuel . BSFC = m g/hr / P kW fuel P = (Brake) Power kW Brake = gross indicated + pumping + friction T = (Brake) Torque Nm = Work = W BMEP = Brake mean effective pressure = net indicated + friction . m = fuel mass flow rate g/hr fuel BSFC = Brake specific fuel consumption 9 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Engine Power Heywood, 1988 Indicated power of IC engine at a given speed . is proportional to the air mass flow rate, m air . P = h . m N. LHV . (F/A) / n f air r h = fuel conversion efficiency f LHV = fuel lower heating value F/A fuel-air ratio m /m f air n = number of power strokes / crank rotation r = 2 for 4-stroke Efficiency estimates: SI: 270 bsfc 450 g/kW-hr Diesel: 200 bsfc 359 g/kW-hr h = 1/46 MJ/kg / 200 g/kW-hr = 40-50% f 500 MW GE/Siemens combined cycle gas turbine natural gas power plant 60% efficient SGT5-8000H 530MW 10 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling 4-stroke (Otto) cycle “Suck, squeeze, bang, blow” 1. Intake: piston moves from TDC to BDC with the intake valve open, 180 BDC W  pdv pdv drawing in fresh reactants in,gross  180 BDC 2. Compression: 3 valves are closed and piston moves from BDC to TDC, (net = gross + pumping) Combustion is initiated near TDC 3. Expansion: W pdv high pressure forces piston in,net  from TDC to BDC, transferring work to crankshaft 2 4. Exhaust: exhaust valve opens and piston moves 1 4 from BDC to TDC pushing out exhaust 1,4 Pumping loop – An additional TDC BDC rotation of the crankshaft used to: Four-stroke diesel pressure-volume - exhaust combustion products diagram at full load - induct fresh charge 11 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Combustion process - initiated near end of compression stroke. Instantaneous combustion has high theoretical efficiency, but is impractical due to need to manage peak pressures and due to high heat transfer. Spark-ignition engine: mixture of air (oxygen carrier) and fuel enters chamber during intake process. Mixture is compressed - combustion initiated using a high-energy electrical spark. Compression-ignition (Diesel) engine: air alone is drawn into chamber, compressed. Fuel injected directly into chamber near end of compression process. (Fuel used in compression-ignition engine must easily spontaneously ignite when exposed to high temperature and pressure compressed air.) Diesel is often portrayed as having a slower combustion process (constant pressure instead of constant volume) Goal of rapid combustion near TDC for maximum efficiency is true for both Diesel and spark-ignition engines. 12 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Thermodynamics review – Zero’th law 1. Systems in thermal equilibrium are at the same temperature 2. If two thermodynamic systems are in thermal equilibrium with a third, they are also in thermal equilibrium with each other. B 300K A 300K Thermal equilibrium 300K C 13 CEFRC1-1 2014 = system Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Thermodynamics review - First law During an interaction between a system and its surroundings, the amount of energy gained by the system must be exactly equal to the amount of energy lost by the surroundings Engine System Surroundings Gained (input) (J) Lost (output) (J) - Work Gained (J) Intake flow + Heat Lost (Cylinder wall, Lost (J) Energy of fuel Exhaust gas ) combustion Friction 14 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Thermodynamics review - Second law The second law asserts that energy has quality as well as quantity (indicated by the first law)  q ds ds irrev T ds 0 irrev Engine research: Reduce irreversible Increase thermal losses efficiency 15 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Equations of State where Thermal: R R /W Pv RT u Caloric: de c dT and dh c dT p v Enthalpy: h e Pv c  R R p c Ratio of specific heats:  c p v 1 c1 v Calculation of Entropy 2 Tds de vdP Gibbs’ equation: P TP 22 1 s s c ln R ln 21 p TP 11 and Tv 22 s s c ln Rln 21 v Tv v 11 16 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Isentropic process Adiabatic, reversible ideal reference process TP 22 0 s s c ln R ln 21 p TP 11  /(1)  p v T 2 1 2   p v T 1 2 1 Tv 22 0 s s c ln R ln 21 v 2 Tv 11 P 1 v 17 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 Ideal cycles Diesel Otto T T 3 3 2 2 1 1 4 4 s s 1-2 Isentropic compression 1-2 Isentropic compression 2-3 Constant volume heat addition 2-3 Constant pressure heat addition 3-4 Isentropic expansion 3-4 Isentropic expansion 4-1 Constant volume heat rejection 4-1 Constant volume heat rejection 18 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Constant volume combustion - HCCI: T t t begin end T burn Isentropic During constant volume expansion combustion process: t 1100K - t 0 begin end 800K t end W Pd 0 Shaft  Motored t Isentropic begin compression t end TDC Q Qdt mQ f LHV  t begin  (1) T  T m Q burn unburn f LHV R 19 CEFRC1-1 2014 Part 1: IC Engine Review, 0, 1 and 3-D modeling Heywood, 1988 8 Zero-Dimensional models measured 7 predicted 6 5 4 measure Single zone model 3 p() 2 V() 1 st 1 Law of Thermodynamics 0 -80 -60 -40 -20 0 20 40 60 80 Crank Angle, deg. dT dV  mc p m hq qq  v j j Comb Loss Net dt dt j 350 300 Use the ideal gas equation to relate p & V to T 250 dV 1 dpV 200 qp Net dt 1 dt 150 100 where qhA(T T ) 50 Loss wall 0 -50 Assume h and T wall -20 -10 0 10 20 30 40 50 60 Crank angle (degree) 20 CEFRC1-1 2014 Heat release rate (J/degree) Pressure, MPa