MIT OpenCourseWare http ocw mit edu 2 61 Internal Combustion Engines Spring 2008 For information about citing these materials or our Terms of Use visit http ocw mit edu terms MASSACHUSETTS INSTITUTE OF TECHNOLOGY Department of Mechanical Engineering 2 615 INTERNAL COMBUSTION ENGINES Homework Set 4 Due 3 11 08 Problems 1 Problem 6 1 of text book Think about under the same engine speed and BMEP why would the inlet manifold pressure and thus the Pumping MEP be different for the two fuels 2 This problem is an exercise to get an idea of the flame propagation environment under typical engine condition In the problem set directory the simulation results for operating an engine under vehicle cruise condition see engine specification below are tabulated in the ascii file si sim oum The columns are explained in the matlab m file si sim m and also documented below If you are using matlab executing the m file si sim m will automatically load the data file into the various variables if you want to use Excel you can import the file into a spread sheet Engine specification 1500 rpm intake pressure 38 kpa 1 ignition at 30o BTC Bore 86 mm stroke 86 mm con rod to bore ratio 1 58 Clearance vol 58 77 cc Plot the following quantities as a function of the mass burned fraction Use Eq 9 36 for the laminar flame speed calculation The residual gas mole fraction is 20 After the plots by the computer take a look at the values to appreciate the magnitude of the various quantities Good engineers scientists should always know the numbers for the phenomena they are working on i ii iii iv v vi vii The unburned and burned gas temperatures The pressure The laminar flame speed The laminar flame expansion velocity The mass fraction burn rate d xb d The volume of burned gas as a fraction of the charge volume Assuming that the engine has a flat head and a flat piston and assuming that the burned gas occupies a cylindrical volume of radius R and a height equals to the combustion chamber height plot the ratio of 2R B where B is the bore In reality the flame ball is more likely to be roughly hemispherical at first until it touches the piston then it will transition into a cylindrical geometry 3 Problem 9 4 of text book The problem illustrates the effects of spark plug location and combustion chamber shape on burn rate For Problem 2 the columns of data in the file si sim are theta si sim 1 p si sim 2 tu si sim 3 tb si sim 4 m int si sim 5 m exh si sim 6 viv si sim 7 vexh si sim 8 xb si sim 9 x net si sim 10 qdot h si sim 11 w pist si sim 12 crankangle pressure bar unburned gas temp k bunred gas temp k cumulative mass inducted g cumulative mass exhausted g velocity at intake valve m s velocity at exhaust valve m s mass fraction burned net ht rel LHV fuelmass heat transfer J deg work transfer to piston Kj