Medium/Heavy Duty Truck Engines Chapter 11

Medium/Heavy DutyTruck Engines, Fuel & Computerized Management Systems, 3EChapter 16Chemistry & CombustionCopyright 2009 Delmar, Cengage LearningIntroductionKnowledge of chemistry important to:Understand fuel composition & combustion dynamicsDevelop ability to work with electricity & electronics

Copyright 2009 Delmar, Cengage LearningBasic ChemistryBuilding blocks of all matter are atomsAll atoms are electricalElectrical charge is a component of all atomic matter

Copyright 2009 Delmar, Cengage LearningElementsAn element is any one of more than 100 substances that cannot be chemically resolved into simpler substancesElements consist of minute particles known as atomsExamples:Hydrogen AtomOxygen Atom

Copyright 2009 Delmar, Cengage LearningCommon ElementsMetallic ElementsAtomic #Non-Metallic ElementsAtomic #Iron Fe26Hydrogen H1Sodium NA11Carbon C6Magnesium Mg13Helium HE2Aluminum Al13Sulfur S16Nickel N28Silicon Sl14Rhodium Rh35Selenium Se34Silver Ag47Oxygen O8Zinc Zn30Nitrogen N7Gold Au79Argon Ar18Platinum - Pt78Radon - Rn86Atomic # identifies number of protons in an atom of the elementCopyright 2009 Delmar, Cengage LearningMixturesA mixture is composed of two or more elements and/or compoundsFor example:Air = 23% oxygen + 76% nitrogen + 1% inert gasesBoth oxygen & nitrogen: Retain their own identityRetain their own characteristicsCan take part in reactions independently of each otherMixture properties depend on the substances in itCopyright 2009 Delmar, Cengage LearningChemical BondingsInteractions accounting for the association of atoms into molecules, ions, crystalsWhen atoms approach each other:Their nuclei & electrons interactDistribute themselvesTheir combined energy is lower than in the alternative arrangementValency Number:Number of bonds an atom can formValency of an atom is simply the number of unpaired electrons in its valence shellCopyright 2009 Delmar, Cengage LearningCompoundsA compound is composed of:Two or more elementsCombined in definite proportionsHeld together by a chemical forceCan be broken down into their elements by chemical reactionsCarbon atoms are uniqueHave ability to form covalent bondsWith each otherWith other elementsCovalent bonding occurs when two electrons are shared by two atoms.Pure compounds can be obtained by physical separation processes such as filtration & distillationCopyright 2009 Delmar, Cengage LearningMolecules

A molecule is:Smallest particle of a compoundCan exist in a free stateCan take part in a chemical reactionA water moleculeNote:Shared electronsAn oxygen moleculeCopyright 2009 Delmar, Cengage LearningAtomic StructureElectronCarries negative chargeOrbit in shells around atoms nucleusProtonCarries positive chargeLocated in atoms nucleusNeutronElectrically neutralLocated in atoms nucleusCopyright 2009 Delmar, Cengage LearningBalanced AtomsElectrically balanced atoms have an equal number of electrons & protonsAn atom with either a deficit or surplus of electrons is called an ion

Copyright 2009 Delmar, Cengage LearningBalanced AtomsElectrons are arranged in circular orbits around the nucleus

Electrical force attracting the electron to the positive charge of the nucleus is offset by the mechanical force acting outwards on the rotating electrons keeping them in their orbits.Copyright 2009 Delmar, Cengage LearningStates of MatterGenerally classified into one of three states or phasesSolidLiquidGas

Water is the only substance that is familiar with all three states: Ice (solid)Water (liquid)Steam (gas)Copyright 2009 Delmar, Cengage LearningDetermining StateDifference between solids, liquids & gases can be explained in terms of kinetic molecular theoryKinetic = motionAs temperature increases, so does molecular motionVaporization: heat applied to liquid, converts to gaseous stateCondensation: reverse vaporization

Copyright 2009 Delmar, Cengage LearningStates of Matter - ConclusionTypical injector pulse:Fuel directly injected to diesel engine cylinder is atomized (liquid state)Exposed to heat of compression (vaporizes)Gases condensing in exhaust observed as white smokeCopyright 2009 Delmar, Cengage LearningProperties of Mixtures & CompoundsEach element has:A special identityA set of characteristics that make it uniqueChemical Reactions:Explained by their constituent elementsCombustion is an oxidation reactionReactant in engine cylinder is whatever oxygen present at time of ignitionCopyright 2009 Delmar, Cengage LearningProperties of Common ElementsElementStateAtomic #Properties/CharacteristicsHydrogenGas1Simplest element, one of the most reactiveCarbonVaries6Combines to form compounds more readily than other elementsOxygenGas8Most common element in earths crustNitrogenGas7When oxidized in the combustion process, it forms several compounds collectively known as NoxSulfurSolid16Appears prominently in residual oilIronSolid26Used extensively in vehicle technology, mostly as steelAluminumSolid13Excellent conductor of heat & electricityMost fuels are elementally composed of carbon & hydrogen

Copyright 2009 Delmar, Cengage LearningCombustion ReactionsInvolved Products & Byproducts:Air (a mixture)NitrogenN278.084%OxygenO220.946%ArgonAr00.934%NeonNe00.0018%HeliumHe00.000524%MethaneCH400.0002%KryptonKr00.000114%HydrogenH200.00005%Nitrous oxideN2O00.00005%ZenonXe00.0000087%

Copyright 2009 Delmar, Cengage LearningCombustion ReactionsInvolved Products & Byproducts:Water vaporH2O0 7%OzoneO3 0.01%Carbon DioxideCO20.01 0.1%Carbon MonoxideCOSulfur OxidesSOxOxides of NitrogenNOx

Byproducts of combustionCopyright 2009 Delmar, Cengage LearningUnburned HydrocarbonsUHCs consist of any emitted unburned fuel fractionsInclude:ParaffinsOlefinsAromaticsLeast volatile elements of a fuel more likely to result in UHC emissionsClassified as potentially harmfulCopyright 2009 Delmar, Cengage LearningPartially Burned HydrocarbonsPHCs are a result of low-temperature combustionInclude:AldehydesKetonesCarboxylic acidsCan result from extinguishing the flame front before a molecule is completely combusted.Copyright 2009 Delmar, Cengage LearningParticulate MatterAny liquid or solid matter emitted from exhaust stackCan be detected in light extinction test apparatus (i.e. smoke opacimeter)Classified as particulate matter (PM)The term PM is more appropriately applied to emitted ash & carbon spots in the solid stateCopyright 2009 Delmar, Cengage LearningCombustionFuel+ Oxygen+ Heat= Chemical ReactionHeatTo ignition temperature!

The reaction causes the energy in the fuel to be liberated resulting in a large volume of hot gases!Copyright 2009 Delmar, Cengage LearningCombustion with Ambient AirCombustion in an engine cylinder uses the oxygen available in the ambient air mixtureProportionally the largest ingredient of the reaction is always nitrogenIdeally nitrogen should remain inert, unaffected by the oxidation of the fuelWhen nitrogen is oxidized, NOx are producedNoxious emissionsCopyright 2009 Delmar, Cengage LearningCombustion in an Engine Cylinder

Pressure volume curve in a diesel engine.The large volume of hot gases produced as a result of the combustion reaction creates this pressure.Copyright 2009 Delmar, Cengage LearningCylinder Gas DynamicsInjected fuel is:DispersedMixedCombusted in the cylinderIntent is to create cyclonic turbulence in the cylinder as the piston is driven upwardsBehavior governs:Engines performance efficiencyNoxious emissions

SwirlCopyright 2009 Delmar, Cengage LearningStoichiometryActual ratio of the reactants in any reaction to the exact ratios required to complete the reactionStoichiometric ratio or lambda () factor is dependent on actual chemical composition of the fuel to be burned> = greater than, < = less than= Actual air supplied Stoichiometric requirement> 1 lean burn< 1 rich burn = 1 stoichiometric AFRCopyright 2009 Delmar, Cengage LearningCalculating Air-Fuel RatioPetroleum contains by mass:Carbon 84 87 %Hydrogen 11 15 %Sulfur0 -- 2 %For oxidization:1 Kg. of carbon (C) requires 2.66 KG. of Oxygen (O)1 Kg. of hydrogen (H) requires 8.0 Kg. of Oxygen (O)1 Kg. of Sulfur (S) requires 1.0 Kg. of Oxygen (O)Air contains approximately 23% by mass1 Kg. of air would contain .23 Kg. of Oxygen1 Kg. of oxygen is contained in 4.35 Kg. of airCalculating an Air-Fuel RatioWith a hypothetical diesel fuel containing by mass; 86% carbon, 13% hydrogen & 1% sulfur the oxygen required to completely oxidize 1 Kg. of the fuel would be:Carbon (2.66 X .86) + Hydrogen (8 X .13) + Sulfur (1 X .01) = 14.5 Kg.The air fuel ratio for this example would be 14.5:1Copyright 2009 Delmar, Cengage LearningCombustion CycleIgnition delay or ignition lagOccurs between start of ignition & the moment ignition occursPeriod of rapid combustionFuel that evaporated & mixed during ignition delay period is burned, the rate & duration of rapid combustion are closely associated with the length of the delay periodThird phase of combustionBegins at the moment of peak cylinder pressure & ends when combustion is measurably complete

Available fuel is oxidized.injector nozzle opening.Copyright 2009 Delmar, Cengage LearningCombustion CycleAfterburn phaseA period in which any unburned fuel in the cylinder may find oxygen & burnDosing InjectionFinal shot of fuel into the cylinder, not intended to be combusted in the cylinder. Shot is injected with intention of discharging into the exhaust system as raw fuel to be combusted in exhaust gas aftertreatment systems

Copyright 2009 Delmar, Cengage LearningCombustion CycleDetonationMultiple flame front condition that causes an abnormally high rate of combustion & resultant pressure rise in the cylinder blockDiesel knockPingCopyright 2009 Delmar, Cengage Learning