Automotive (caused) Air Pollution

Introduction: While surfing the net recently (2021-02-15) I began bumping into articles and blog posts about the Volkswagen AG debacle going by the meme Dieselgate. Most blogs contain a lot of errors, while some of the articles contain a little misinformation. I believe this is partly due to the fact that many modern citizens skipped secondary school chemistry, or know next the nothing about technology. Simply put, Dieselgate cannot be fully understood without understanding things like:

  1. what is smog?
  2. how did initial industry efforts to reduce polution only changed smog color?
  3. how do automobile manufacturers reduce smog this side of Y2K?
  4. what is the 'Coles Notes' version of Dieselgate?

This article is not yet complete (I have been called away to deal with other more-pressing issues)

Setting the stage

In 1965 Canada and the USA, passenger automobiles and small trucks were powered by gasoline (petrol for you Brits) which was relatively cheap (45 cents per Imperial gallon).  Buses and large trucks were powered by diesel which usually belched black smoke during acceleration. Since gasoline was cheap, and everyone wanted to go fast, every red-blooded male wanted to own a muscle car. But two were problems looming.

  1. POLLUTION: There have always been national clean air clean legislation in the USA (here are two examples: 1956 and 1963) but the American nation started thinking differently after the Apollo manned missions to the moon returned pictures of a fragile Earth floating in space. With pressure from both political parties, Richard Nixon created the EPA ( Environmental Protection Agency ) in 1970 with a mandate to start prosecuting environmental laws in order to protect air and water.
     
  2. PRICE: In 1973, a coalition of Arab nations attacked Israel in what is now known as the Yom Kippur War. The Nixon administration backed Israel which triggered the Arab nations to seek revenge by having OPEC embargo oil exports to North America. That immediately elevated the price per barrel of crude oil from $3 to $12. Since then the price of oil has skyrocketed and gasoline followed.

Smog

Smog has been around since before the start of the industrial revolution. Yellow Smog was first observed in Great Britain and was usually associated with burning high-sulfur coal (eg. Lignite is one example). I mention this here because non-technical people reported seeing yellow smog in California during the late 1960s where virtually no one was burning coal but every family seemed to own two cars. Also at that time, people reported seeing brown smog as well as gray smog.

Scientists and engineers know that the color of NO2 (nitrogen dioxide) can be perceived as reddish-orange to reddish-brown so now we have a possible explanation for the brown smog. In the presence of water, NO2 can be transformed to HN03 (nitric acid) which is pale yellow, and this is a possible explanation for yellow smog seen in California.

Grey smog is usually associated with soot produced by burning coal (or wood) but since California is a warmish state engineers assumed this was unburned hydrocarbons from cars (so gasoline) or buses and trunks (so diesel)

Improving Engine Efficiency

Energy is lost whenever any engine, either gasoline or diesel, is releasing unburned hydrocarbons (CHx), carbon monoxide (CO) or soot (C). Solutions include:
 
  1. increasing the oxygen/fuel ratio
    • Carburetors
      • Fifty-years ago, most lower cost vehicles employed a carburetor to mix fuel with atmospheric air before presenting it to engine cylinders. A carburetor is nothing more than a glorified perfume atomizer where the starting mixture is controlled by turning a screw (rich vs lean). My property maintenance machines (snow blower, lawn mower, whipper-snipper) in 2021 all employ carburetors.
      • A simple carburetor tuned to work efficiently at sea-level might not behave properly when you drive to a mountainous area where atmospheric air pressure is lower, so mechanical feedback mechanisms were introduced to add-to, or subtract-from, the starting setting
    • Supercharger (and turbocharger)
      • Things were different in the aircraft industry where huge changes in pressure and temperature made carburetor use unreliable. So many non-jet aircraft designers employed superchargers to ensure that sufficient air and fuel were always available. Most people today seem to be unaware of the fact that superchargers predate the invention of powered flight and horseless carriages.
      • Initially, superchargers were only available on expensive most racing equipment as well as expensive European autos but as time moved forward they began to appear in the consumer space.
      • BTW, a supercharger is a pump which requires power which, almost always, comes from the engine via a crankshaft belt. Superchargers powered by engine exhaust are called turbochargers
  2. improving fuel evaporation from a liquid to a gas
    • according to Boyle's law, a supercharger (or turbocharger) will cause fuel droplets to evaporate as soon as the pressure is increased.
    • preheat the air-fuel mixture by allowing engine heat to warm the intake manifold  
  3. improving engine design
    1.  Wikipedia's article titled Chrysler's hemispherical engine is good so i won't repeat this here

Details about burning Gasoline ('petrol' for you Brits)

CO2 moleculeAt first glance it seems impossible (to a non-scientist) that:
burning one U.S. gallon (3.8 L) of octane (C8H18)
which weighs approximately 6 pounds (2.7 Kg)
will produce produce produce 18 pounds (8.16 Kg) of carbon dioxide (CO2)

However, most of the weight of CO2 does not come from the gasoline itself, but the oxygen from the atmosphere. When gasoline burns, the carbon and hydrogen separate. The hydrogen combines with oxygen to form water vapor (H2O) while the carbon combines with oxygen to form carbon dioxide (CO2). A carbon atom has an atomic weight of 12, and each oxygen atom has an atomic weight of 16, giving each single molecule of CO2 an atomic weight of 44 (12 + 2 x16 ). It now appears that that Carbon Capture and Storage (CSS) technology will never be practical since the required amount of energy to compress-store this volume of gas would be too large.
 

  • The players in this drama
    Substance Chemical Formula Notes
    Molecular Oxygen O2
    Octane (gasoline or petrol) C8H18
    Carbon Dioxide CO2
    Water H2O
    Molecular Nitrogen N2 an inert gas at room temperature
  • Atomic Masses from the Periodic Table:
    Element Atomic Number Atomic Mass
    Hydrogen 1   1
    Carbon 6 12
    Oxygen 8 16
  • (balanced) Burn Equation: 2 C8H18 + 25 O2 → 16 CO2 + 18 H2O (reference)
  • Gasoline Mass Calculation
    • Total octane mass (from the left-hand side of the equation):
      • 2 x ((C x 8) + (H x 18))
      • 2 x ((12 x 8) + (1 x 18))
      • 2 x (96 + 18)
      • 2 x 114 = 228
    • Total Oxygen Mass (from the left-hand side of the equation):
      • 25 x (O x 2)
      • 25 x (16 x 2)
      • 25 x 32 = 800
  • Carbon Dioxide Mass Calculation
    • Total Carbon Dioxide mass (from the right-hand side equation):
      • 16 x ((C x 1) + (O x 2))
      • 16 x ((12 x 1) + (16 x 2))
      • 16 x (12 + 32)
      • 16 x 44 = 704
    • Ratio: 704 / 228 = 3.09 (therefore the resultant CO2 is ~ 3 times heavier than gasoline)
  • Water Vapor Mass Calculation
    • Total Water Vapor mass (from the right-hand side equation):
      • 18 x ((H x 2) + (O x 1))
        • 18 x ((1 x 2) + (16 x 1))
      • 18 x (2 + 16)
      • 18 x 18 = 324
    • Ratio: 324 / 228 = 1.42 (therefore the resultant water vapor is ~ 1.4 times heavier than gasoline)

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Neil Rieck
Waterloo, Ontario, Canada.