Measurement Seminar Presentation PPRE 2005-2007 G. Pechlivanoglou Heat of Combustion – Heat of Evaporation
Combustion Evaporation HCCI 0 Gravity Combustion Combustion is an exothermic reaction between a fuel and an oxidizer (usually O2),which releases heat. Fuel + Oxygen → Heat + Water + Carbon Dioxide General Chemical Reaction of Organic substance Combustion CxHy + (x + y/4)O2 → xCO2 + (y/2)H2O Example: Propane Combustion: C3H8 + 5O2 → 3CO2 + 4H2O
Combustion Evaporation HCCI 0 Gravity Combustion Combustion phases Preheating phase: unburned fuel is heated up to its flash point. Gaseous phase: the mix of evolved flammable gases with oxygen is ignited. Solid phase:the charred fuel does not burn rapidly anymore but just glows and later only smoulders.
Combustion Heat of Combustion Evaporation HCCI 0 Gravity Combustion Fuel HHV MJ/kg HHV BTU/lb LHV BTU/kg Hydrogen 141.6 61,000 --- Gasoline 47.3 20,400 19,000 Diesel 44.8 19,300 18,200 Ethanol 29.7 12,800 11,500 Butane 48.6 20,900 18,900 Wood 15 6,500 --- Coal 15-27 8,000 - 14,000 --- Heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen HHV (Higher Heating value):Maximum Potential Energy of Combustion [exhaust H2O is in liquid form] LHV (Lower Heating Value):Total Energy of combustion (-) Energy for produced water vaporization [exhaust H2O is in vapour form] GHV (Gross Heating Value):Energy of combustion (-) Total Energy of ALL water vaporization (includes also liquid water in the fuel prior to combustion)
Combustion Evaporation HCCI 0 Gravity Combustion Evaporation:The process whereby atoms or molecules in a liquid state gain sufficient energy to enter the gaseous state. Heat of Vaporization (Latent Heat):The heat demand for complete evaporation of a unit mass of a substance at its boiling point.
Combustion Evaporation HCCI 0 Gravity Combustion Both Combustion & Evaporation take place the same time in all the Thermal Engines and Combustors • Theoretically, water evaporation reduces the engine’s output. • With some types of fuel the evaporation is even higher due to water existence in the fuel prior to combustion (e.g. wood, coal) • Water Evaporation has also positive effects (in ICE) as is lowers the comb. chamber temperature preventing pre-ignition • Studies show that water evaporation has also some even more advantageous, but poorly studied characteristics (e.g. high ratio water injection)
Combustion Evaporation HCCI 0 Gravity Combustion • Water Injection (5-25% of fuel mass) reduces the combustion chamber temperature due to evaporation and prevents pre-ignition • (compression ratio – efficiency & power will be increased) • Water Injection (40% of 106octane fuel mass) increases the power output by 52%! • Water Injection (150% of 80octane fuel mass) increases the power output by 251%!!! Tremendous increase in Fuel Efficiency and Power Output
Combustion Evaporation HCCI 0 Gravity Combustion Homogeneous Charge Compression Ignition (HCCI) combustion Homogeneous Charge Compression Ignition (HCCI) combustion • Efficiency as high as for Diesel. • Very low emissions of soot and NOx. • Fuel consumption benefit of 20-25% compared to SI. • Auto-ignition by compression. • Ignition and combustion controlled by chemistry. • Mixture not perfectly homogeneous!
Combustion Evaporation HCCI 0 Gravity Combustion • Advantages • HCCI combustion is extremely fast so it is closer to the ideal Otto cycle than SI combustion. • Lean operation leads to higher efficiency than in spark ignited gasoline engines • Lower emissions due to the fact that peak temperatures are significantly lower than in SI engines, NOx levels are almost negligible. • Since HCCI runs throttleless, it eliminates throttling losses
Combustion Evaporation HCCI 0 Gravity Combustion SI & HCCI Comparison Animation Note the high HCCI combustion speed and the almost spontaneous combustion of the whole chamber volume
Combustion Evaporation HCCI 0 Gravity Combustion • Disadvantages • High peak pressures • High heat release rates • Difficulty of control • Difficulty of increasing power Honda HCCI test engine
Combustion Evaporation HCCI 0 Gravity Combustion Combustion Characteristics & Behavior of Flames In Zero Gravity Environment Combustion Characteristics & Behavior of Flames In Zero Gravity Environment • The lack of gravitational forces prevents the buoyancy effects. • The combustion is more efficient and symmetric. • There are also differences in the heat transfer mechanisms from the flame to the environment
Combustion Evaporation HCCI 0 Gravity Combustion Flame Patterns in Zero Gravity Flame Patterns in Zero Gravity
Combustion Evaporation HCCI 0 Gravity Combustion Diesel auto-ignition in normal gravity Diesel auto-ignition in zero gravity
References: • NACA Resource Center • Wikipedia (www.wikipedia.org) • Univ. Berkeley HCCI (http://www.me.berkeley.edu/cal/HCCI/) • Chalmers Univ. of Technology HCCI (http://www.tfd.chalmers.se/~ogink/) • Stanford Univ. HCCI (http://www-cdr.stanford.edu/dynamic/hcci_control/) • NASA Glenn Research Center (http://microgravity.grc.nasa.gov/)