Diesel Cycle

Introduction

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  Diesel Cycle

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  Diesel Cycle

Ratio of specific heats (heat capacity ratio) is defined as $\gamma ={\frac {C_{p}}{C_{v}}}$

1. Isentropic (adiabatic) expansion
2. Isochoric cooling (Qout): Heat rejection. Power stroke ends, heat rejection starts.
3. Isobaric compression: Exhaust
4. Isobaric expansion: Intake
5. Isentropic (adiabatic) compression
6. Isobaric heating (Qin): Combustion of fuel (heat is added in a constant pressure;)

Engine displacement is the cylinder volume swept by all of the pistons of a piston engine, excluding the combustion chambers. A combustion chamber is part of an internal combustion engine in which the fuel/air mix is burned.

Realistic Diesel Cycle

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  The size of the combustion chamber of MB W211.

Diesel-air Mixture

The heat capacity ratio (known as the adiabatic index) for a diesel-air mixture is typically around 1.4.

heat capacity ratio Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \gamma</gamma> |- | 14.5:1 || Near-stoichiometric; good combustion efficiency but higher emissions. |- | 16:1 || Balanced performance; good power output and efficiency. |- | 18:1 || Lean burn; improved fuel economy but potential for higher NOx emissions. |} Diesel is a complicated compound, but it’s commonly approximated as a hydrocarbon like C₁₂H₂₃ (or C₁₂H₂₆). Air is about 21% O₂ and 79% N₂. Without nitrogen, the stoichiometric ratio is about C₁₂​H₂₃​+17.75O₂​→12CO₂​+11.5H₂​O and by including nitrogen, we get C₁₂​H₂₃​+17.75( O₂ + 3.76 N₂ )​→12CO₂​+11.5H₂​O + 66.74 N₂. The molar masses * Fuel: 167 g/mol * Air: 137.28 g/mol And the total air needed is 17.72 x 137.28 = 2436 g, which gives air-to-fuel-ratio to <math> AFR = \frac{2436}{167} = 14.6:1 }

MB data

Mercedes Benz W211 (2003)

• Engine displacement: 3222 cm³
• Bore x Stroke: 88.0 x 88.4 mm³
• Compression Ratio: 18.0

Bore x stroke gives V = 6xπ(8.8/2)² x 8.84 cm³ = 3225.95cm³, which is rather close.

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