Medium/Heavy Duty Truck Engines, Fuel & Computerized Management Systems, 3E

1. Medium/Heavy DutyTruck Engines, Fuel & Computerized Management Systems, 3E Chapter 16 Chemistry & Combustion

2. Introduction • Knowledge of chemistry important to: • Understand fuel composition & combustion dynamics • Develop ability to work with electricity & electronics

3. Basic Chemistry • Building blocks of all matter are atoms • All atoms are electrical • Electrical charge is a component of all atomic matter

4. Elements • An element is any one of more than 100 substances that cannot be chemically resolved into simpler substances • Elements consist of minute particles known as atoms • Examples: • Hydrogen Atom • Oxygen Atom

5. Common Elements

6. Mixtures • A mixture is composed of two or more elements and/or compounds • For example: • Air = 23% oxygen + 76% nitrogen + 1% inert gases • Both oxygen & nitrogen: • Retain their own identity • Retain their own characteristics • Can take part in reactions independently of each other • Mixture properties depend on the substances in it

7. Chemical Bondings • Interactions accounting for the association of atoms into molecules, ions, crystals • When atoms approach each other: • Their nuclei & electrons interact • Distribute themselves • Their combined energy is lower than in the alternative arrangement • Valency Number: • Number of bonds an atom can form Valency of an atom is simply the number of unpaired electrons in its valence shell

8. Compounds • A compound is composed of: • Two or more elements • Combined in definite proportions • Held together by a chemical force • Can be broken down into their elements by chemical reactions • Carbon atoms are unique • Have ability to form covalent bonds • With each other • With other elements Pure compounds can be obtained by physical separation processes such as filtration & distillation Covalent bonding occurs when two electrons are shared by two atoms.

9. Molecules • A molecule is: • Smallest particle of a compound • Can exist in a free state • Can take part in a chemical reaction Note: Shared electrons A water molecule An oxygen molecule

10. Atomic Structure • Electron • Carries negative charge • Orbit in shells around atom’s nucleus • Proton • Carries positive charge • Located in atom’s nucleus • Neutron • Electrically neutral • Located in atom’s nucleus

11. Balanced Atoms • Electrically balanced atoms have an equal number of electrons & protons • An atom with either a deficit or surplus of electrons is called an ion

12. Balanced Atoms • Electrons 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.

13. States of Matter • Generally classified into one of three states or phases • Solid • Liquid • Gas • Water is the only substance that is familiar with all three states: • Ice (solid) • Water (liquid) • Steam (gas)

14. Determining State • Difference between solids, liquids & gases can be explained in terms of kinetic molecular theory • Kinetic = motion • As temperature increases, so does molecular motion • Vaporization: heat applied to liquid, converts to gaseous state • Condensation: reverse vaporization

15. States of Matter - Conclusion • Typical 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 smoke

16. Properties of Mixtures & Compounds • Each element has: • A special identity • A set of characteristics that make it unique • Chemical Reactions: • Explained by their constituent elements • Combustion is an oxidation reaction • Reactant in engine cylinder is whatever oxygen present at time of ignition

17. Properties of Common Elements

18. Combustion Reactions • Involved Products & Byproducts: • Air (a mixture) • Nitrogen N2 78.084% • Oxygen O2 20.946% • Argon Ar 00.934% • Neon Ne 00.0018% • Helium He 00.000524% • Methane CH4 00.0002% • Krypton Kr 00.000114% • Hydrogen H2 00.00005% • Nitrous oxide N2O 00.00005% • ZenonXe 00.0000087%

19. Combustion Reactions • Involved Products & Byproducts: • Water vapor H2O 0 – 7% • Ozone O3 0.01% • Carbon Dioxide CO2 0.01 – 0.1% • Carbon Monoxide CO • Sulfur Oxides SOx • Oxides of Nitrogen NOx Byproducts of combustion

20. Unburned Hydrocarbons • UHCs consist of any emitted unburned fuel fractions • Include: • Paraffins • Olefins • Aromatics • Least volatile elements of a fuel more likely to result in UHC emissions • Classified as potentially harmful

21. Partially Burned Hydrocarbons • PHCs are a result of low-temperature combustion • Include: • Aldehydes • Ketones • Carboxylic acids • Can result from extinguishing the flame front before a molecule is completely combusted.

22. Particulate Matter • Any liquid or solid matter emitted from exhaust stack • Can 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 state

23. Combustion Fuel + Oxygen + Heat = Chemical Reaction To ignition temperature! The reaction causes the energy in the fuel to be liberated resulting in a large volume of hot gases! Heat

24. Combustion with Ambient Air • Combustion in an engine cylinder uses the oxygen available in the ambient air mixture • Proportionally the largest ingredient of the reaction is always nitrogen • Ideally nitrogen should remain inert, unaffected by the oxidation of the fuel • When nitrogen is oxidized, NOx are produced Noxious emissions

25. Combustion 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.

26. Cylinder Gas Dynamics • Injected fuel is: • Dispersed • Mixed • Combusted in the cylinder • Intent is to create cyclonic turbulence in the cylinder as the piston is driven upwards • Behavior governs: • Engine’s performance efficiency • Noxious emissions “Swirl”

27. Stoichiometry • Actual ratio of the reactants in any reaction to the exact ratios required to complete the reaction • Stoichiometric 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 AFR

28. Calculating Air-Fuel Ratio Calculating an Air-Fuel Ratio With 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 14.5:1 • Petroleum contains by mass: • Carbon 84 – 87 % • Hydrogen 11 – 15 % • Sulfur 0 -- 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 mass • 1 Kg. of air would contain .23 Kg. of Oxygen • 1 Kg. of oxygen is contained in 4.35 Kg. of air

29. Combustion Cycle injector nozzle opening. • Ignition delay or ignition lag • Occurs between start of ignition & the moment ignition occurs • Period of rapid combustion • Fuel that evaporated & mixed during ignition delay period is burned, the rate & duration of rapid combustion are closely associated with the length of the delay period • Third phase of combustion • Begins at the moment of peak cylinder pressure & ends when combustion is measurably complete Available fuel is oxidized.

30. Combustion Cycle • Afterburn phase • A period in which any unburned fuel in the cylinder may find oxygen & burn • Dosing Injection • Final 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

31. Combustion Cycle • Detonation • Multiple flame front condition that causes an abnormally high rate of combustion & resultant pressure rise in the cylinder block • “Diesel knock” • “Ping”