← Notedeck
All engines
·
燃烧学·火焰
en
zh-CN
zh-TW
ja
ko
fr
de
es
pt-BR
tr
it
ar
燃烧学·火焰
12
engines
化学计量空燃比
Stoichiometric air-fuel ratio
CxHy配平 · AFR质量/摩尔 · 甲烷17.2/汽油14.7/氢34.3
From the complete-combustion balance of a fuel CxHyOz, find the exact air-fuel ratio for stoichiometric burn — by mass and by mole
当量比 φ(贫燃 / 化学计量 / 富燃)
Equivalence ratio φ (lean / stoichiometric / rich)
φ=(F/A)/(F/A)st · 贫φ<1/富φ>1 · λ=1/φ · 过量空气
Use φ to tell whether a mixture is lean, stoichiometric or rich, and convert between φ, the air ratio λ and percent excess air
燃烧热(高位热值 vs 低位热值)
Heat of combustion (HHV vs LHV)
HHV vs LHV · 水蒸气潜热 · CH4 55.5/50.0 MJ/kg
How much of a fuel's released heat is usable depends on whether the product water condenses and gives back its latent heat
绝热火焰温度
Adiabatic flame temperature
T_ad=T0+ΔHc/Σncp · CH4~2226K · 化学计量最高
With no heat loss all the combustion enthalpy heats the products — T_ad of methane in air versus equivalence ratio φ
层流燃烧速度 S_L
Laminar flame speed S_L
S_L随φ峰值略富φ≈1.05 · 甲烷0.40/氢2.9 m/s
The speed at which a flat premixed flame front advances into the unburned gas — versus equivalence ratio φ
预混火焰 vs 扩散火焰
Premixed vs diffusion flame
预混本生蓝快低烟 vs 扩散蜡烛黄发光积碳
One knob on a Bunsen burner — the primary aeration — switches between the two flame types
辛烷值与发动机爆震
Octane rating & engine knock
RON/MON · η=1−1/CR^0.4 · 高辛烷抗爆 · 爆震限CR
Higher compression ratio means higher efficiency but more knock; higher-octane fuel resists knock and raises the knock-limited compression ratio
柴油十六烷值与着火延迟
Diesel cetane number & ignition delay
十六烷↑→着火延迟↓→柴油平稳 · 与辛烷相反
Higher cetane number → shorter ignition delay → smoother combustion; the exact opposite of gasoline octane
燃烧排放 vs 当量比
Combustion emissions vs equivalence ratio
热力NOx峰略贫φ≈0.9 · 富时CO/HC升 · 排放权衡
Thermal NOx peaks slightly lean (hottest flame with spare O2); CO and unburned HC climb sharply when rich — no single φ minimises all
可燃极限(空气中的 LFL / UFL)
Flammability limits (LFL / UFL in air)
LFL/UFL · 甲烷5–15/氢4–75/汽油1.4–7.6% · 随温加宽
A fuel–air mixture ignites only between the lower and upper limit
闪点 · 燃点 · 自燃点
Flash point · fire point · autoignition
闪点<燃点<自燃点 · 汽油−43°C易燃/柴油52°C可燃
Three temperatures govern ignition — always flash < fire < autoignition
沃泊指数(燃气互换性)
Wobbe index (gas interchangeability)
W=HHV/√SG · 同Wobbe同孔口同热流 · 燃气互换性
W = HHV / √SG — two gases with equal Wobbe index are interchangeable