Assessment 1 AUTO1032 (Vehicle Power Systems): Individual Engine Modelling Assignment (25% of total assessment)
Vehicle Power-Train Technologies (2010)
Course code: AUTO1032
Course name: Vehicle Power-Train Technologies
The pressure increment dP due to -combustion- and piston work was derived in class for an ideal engine cycle with a finite period of heat release. This can be used to determine the pressure-time history in the engine cylinder and consequently, the cycle work done (by integrating PdV) and thermal efficiency. Use any numerical method you prefer (e.g., spreadsheet, Mathcad, C++ etc.) to solve the equation for dP (in half crank angle increments) and estimate the engine performance. For this analysis, use the Wiebe function shown below to model the mass-burned fraction as a function of crank angle. Make sure that xb = 0 for all values of ? below ? o and that xb = the xb value at ( ? o + ? ? ) for all values of ? above ( ? o + ? ? ) .
Mass fraction burnt (Wiebe function), as seen in class notes
= x b = 1 - e ( - 4 * ( ( ? - ? o ) ? ? ) 2.5 )
Use the following assumptions:
- A compression ratio CR of 10:1, unless specified otherwise
- An engine speed of 600 rpm
- A single cylinder engine with displacement of 612 cc
- Bore = 8.26 cm, Stroke = 11.43 cm, Connecting rod length = 25.4 cm
- All the cylinder contents are heated during “combustion”, not just the mass introduced during the intake stroke
- A stoichiometric mix of octane and air from the intake stroke; 14.7 kg air to every 1 kg of fuel
- The lower heating value of the fuel is 44 MJ/kg
- The pressure and temperature of the cylinder contents at the start of compression is 101325 Pa and 52 degrees C respectively
- The density of air at standard temperature and pressure (15 degrees C and 101325 Pa) is 1.225 kg/m3
- A specific heat ratio ( ? ) of 1.3 should be used and it accounts for heat losses
- If you want the value for Cv, use the specific heat ratio to calculate it
- The engine is operating at wide open throttle (WOT) with no pumping losses
- The pressure and temperature in the cylinder drops instantly to pre-compression conditions at the end of the expansion stroke at bottom dead centre (BDC)
Based on your numerical model and theory taught in class, answer the following questions.
You have 1 attempt at this assignment.
Please press the submit button ONLY after you are comfortable with all your answers.