Can a 1.3 hp Engine Power Our Prototype Car?

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Discussion Overview

The discussion revolves around the power requirements for a prototype car powered by a 1.3 hp engine. Participants explore calculations related to power losses due to road gradient, rolling resistance, and drag, as well as considerations for drivetrain efficiency and operational conditions of the engine.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant calculates power losses due to gradient, rolling resistance, and drag, concluding a total of 1.234 hp required at the wheels.
  • Another participant questions whether the rolling resistance was calculated for all wheels and if a safety factor or acceleration allowance was considered.
  • Concerns are raised about friction in the drivetrain and conversion losses through the powertrain, including the generator.
  • Questions are posed regarding whether the engine will operate at optimum conditions for delivering 1.3 hp.
  • A later reply provides a method for calculating power losses through transmission, suggesting efficiency values for different drivetrain components.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the power calculations and the assumptions made regarding drivetrain efficiency and operational conditions. The discussion remains unresolved regarding the sufficiency of a 1.3 hp engine for the prototype car.

Contextual Notes

Limitations include potential missing assumptions about the drivetrain configuration, the need for a safety factor, and the operational efficiency of the engine under load.

Carvinos
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Hello!
Actually i want to find the required power of an a single cylinder air cooled 4 stroke OHV engine. i have calculated three power losses, power loss against road gradient (Pg), rolling resistance (Pr) and drag (Pd) using the following formulae:
Pg=M*g*v*grad=1.095 hp
M(mass of the prototype car)=120kg, g=9.8 m/s^2, v(prototype car velocity)=13.88 m/s, road gradient= 5% (0.05)
Pr=RRC*M*g*v=0.109 hp
RRC (rolling resistance coefficient)=0.005 for a bicycle tire we are using in our prototype car
Pd=0.5*rho*v^3*Cd*A = 0.030 hp
rho=1.099 kg/m^3, Cd (Coefficient of drag)=0.04 in case of our prototype car, A=0.384 m^2
Net power losses=Pg+Pr+Pd=1.234 hp.
Now please tell me can i use an engine of 1.3 hp of 35cc volumetric capacity in our prototype three wheeled car. Generator is the only accessory that will be connected with the engine to charge the battery.13.88 m/s will be the max. speed of our prototype car, 120 kg is the mass of the prototype with driver. reply soon please
 
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Did you calculate the rolling resistance for all wheels?
Have you applied a safety factor, and an allowance for acceleration (and not just travel at a constant speed)?
Have you considered friction in your drivetrain?
Have you considered conversion losses through the powertrain (including your 'generator'?)
Is your engine going to be operating at optimum conditions for 1.3hp?
 
ok.thnx.tell me please the procedure of how to calculate the power losses of engine through transmission.
 
Carvinos said:
ok.thnx.tell me please the procedure of how to calculate the power losses of engine through transmission.

For every gear set or belt drive set, assume 95% efficiency. For every chain drive set, assume 92% efficiency. Multiply all of them for overall efficiency.

Ex.:

if the power of your engine goes through 3 gear sets before reaching the wheels, your overall efficiency would be 0.95*0.95*0.95 = 0.857. So if you need 1.234 hp at the wheel, you need 1.234 / 0.857 = 1.44 hp at the engine.
 

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