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Combustion
Presented by J.M. Castellanos
Adapted from https://www.whichcar.com.au
Homogeneousmixture
Exotermic subsonic flame
ሶ𝑾…If Tmax and Pmax ~ 5°-10° aTDC
Combustion ends ~15° aTDC (ignition ~ 10° bTDC)
Ignition timing between 10° to 30° bTDC…
25° burn angle
f(rpm, geometry, fuel)
Adapted from: The assessment of ecological parameters of diesel engine supplied with mixtures of canola oil with n-hexane.
Stratified air-fuel
Adapted from: Stratified Charge Combustion in a Spark-IgnitionEngineWith Direct Injection System
Rich
Lean
Low flame speeds!!!
…(Potential Knock… but excess of non reacting gases, lowers T.)
SIE Combustion
5° to 10° aTDC…
Adapted from: Natural Gas Engine Technologies: Challenges and Energy Sustainability Issue. 2018
Spark discharge: 1 ms, T=60000K!
Turbulence makes flame speed 10 x faster than a laminar flame in an stationary gas mixture
Adapted from: Internal Combustion Engines Fundamentals. W.W.Pulkrabek. 2002.
Rate of reaction reduced by low Turbulence, lowtemperture and low mass motion (too close to the walls)
Engine operatingcharacteristics
1. Power operation
2. Cruising operation
3. Iddle and low engine speed
4. Closing throttle at high RPM
5. Cold start
Retarded spark & rich mixtures↓f economy but burns faster↑P near TDC ͢ rough opperation!↑T & No EGR ͢ ↑NOx
Racing cars ͢ Lean mixturesburns slower but combustn ----→aTDC….Keeps ↑P during Powerstroke!!! but ↑T_exhaust & O2 ͢Corrosion!!
EGR! ͢ Advanced SI compensateslow burn… ↑ f economy but ↓ 𝜂𝑡(↓rpm ͢ ↑ht)
↑ intake vacuum ↓rpm ͢ Large exhaustresidual ͢ poor combustión! Then…Rich mixture!! ͢ ↑ emissions(HC,CO) & missfires!
↑ intake vacuum ↑ rpm ͢ Rich mixture!! ͢ poor combustión, ↑ emissions & missfires … Carburators!
↓T cilinders, ↓T oil & ↓T fuel ͢ Rich mixture!! Towarrant fuel evaporation!!
Adapted from: Diesel combustion in high load situations: a visual analysis of mixture formation and air utilization. 2017
1. Atomization
2. Vaporization
3. Mixing
4. Self-ignition
5. Combustion
Tair ↑ ...Minimum rc 12:1
90% vaporized after 1 ms…. But there is evaporative cooling!!
…Thanks high fuel injection, swirl and turbulence!! Combustion in zones: ϕ=1.8 - 0.8
…injection holes up to 0.1mm!!
…last abaut 40°- 50°!!..last more than fuel injection ,
because fuel particles take t to mix..
…uncontroled combustión: mixture quickly consumed at the begining....controled combustión by rate & timing of injection.
CIE Combustion
Adapted from: Automotive Basics. https://www.youtube.com/user/TheAutoPartsShop/about
…6°- 8° after injection starts !
Variable compression ratio
Adapted from: https://www.caranddriver.com/ Infiniti's KR20 Variable Compression Turbocharged Engine
Adapted from: https://gfycat.com/.Overal, an automóvil´s small-displacement-engine is generaly more efficient than a lange one!!
…A large SI engine can run efficienly at heavy loads (WOT), but at light loadsthrottle is closed (PT)...
https://youtu.be/YJXu2GJTYZQ
Cylindersdeactivation
(fixed and Dynamic)https://youtu.be/7ijmRV5Y2Y8
Emissions Control
1. Thermal converters
2. Catalytic converters
3. Chemical converters
https://youtu.be/GnlfruquBp8
https://youtu.be/p8clK9qSGlk
https://youtu.be/W6dIsC_eGBI
https://youtu.be/DXfw-sIQUws
https://youtu.be/YGGM1h7xapU
Noise Control
Adapted from: https://www.123rf.com/photo_87963541_stock-vector-exhaust-system-infographic-diagram-showing-all-components-and-parts-including-catalytic-converter-co.html
Exhaust Tuning
https://www.mazda.com/en/innovation/technology/skyactiv/skyactiv-g/Residual gas reduction by 4-2-1 exhaust system
