Question

A reciprocating engine for light aircraft, modeled after the Avco Lycoming O-235 engine, has the following characteristics: bore =11.1 cm, stroke =9.84 cm, number of pistons =4, compression ratio =6.75, mechanical efficiency =0.83. It is connected to a propeller with an efficiency of 0.85. If the fuel-to-air ratio is 0.06 and the pressure and temperature in the intake manifold are 1 atm and 285 K, respectively, calculate the power available from the engine-propeller combination at 2800rpm.

Answer 1

The power available from the engine-propeller combination at 2800 rpm is approximately 214,556.8 watts or 214.56 kW.

To calculate the power available from the engine-propeller combination, we'll follow these steps:

1. Calculate the displacement volume (Vd) of the engine:

Vd = (π/4) x (bore^2) x stroke

Vd = (π/4) x (0.111 m)^2 x 0.0984 m

Vd ≈ 0.001005 m^3

2. Calculate the air mass flow rate (ṁ) into the engine:

ṁ = (P1 / (R * T1)) x Vd

ṁ = (1 atm / (287.1 J/(kg·K) * 285 K)) x 0.001005 m^3

ṁ ≈ 0.1301 kg/s

3. Calculate the fuel flow rate (ṁ_fuel) based on the fuel-to-air ratio:

ṁ_fuel = ṁ x fuel-to-air ratio

ṁ_fuel = 0.1301 kg/s x 0.06

ṁ_fuel ≈ 0.0078 kg/s

4. Calculate the lower heating value (LHV) of the fuel. The LHV for aviation gasoline is typically around 43 MJ/kg.

5. Calculate the energy input from the fuel:

Energy_input = ṁ_fuel x LHV

Energy_input = 0.0078 kg/s x 43,000,000 J/kg

Energy_input ≈ 335,400 J/s (Watt)

6. Calculate the brake horsepower (BHP) of the engine:

BHP = (ṁ_fuel x LHV) / (η_mechanical x 4.184)

BHP = (0.0078 kg/s x 43,000,000 J/kg) / (0.83 x 4.184)

BHP ≈ 244.6 HP

7. Calculate the shaft horsepower (SHP) of the engine:

SHP = BHP / η_propeller

SHP = 244.6 HP / 0.85

SHP ≈ 287.29 HP

8. Finally, convert SHP to watts (W):

1 HP = 745.7 W

Power_available = SHP x 745.7

Power_available ≈ 214,556.8 W

So, the power available from the engine-propeller combination at 2800 rpm is approximately 214,556.8 watts or 214.56 kW.