{
"metadata": {
"name": ""
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"worksheets": [
{
"cells": [
{
"cell_type": "heading",
"level": 1,
"metadata": {},
"source": [
"Chapter11:Two Stroke Engines"
]
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.1 page no:367"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Input data\n",
"nsc=75 #The scavenging efficiency of the two stroke engine in percent \n",
"ns=20 #The scavenging efficiency is increased by in percent\n",
"\n",
"#Calculations\n",
"import math\n",
"Rsc=math.log(1/(1-(nsc/100.0)))\n",
"nsc1=(nsc/100.0)+((nsc/100.0)*(ns/100.0))\n",
"Rsc1=math.log(1/(1-(nsc1)))\n",
"Rscr=((Rsc1-Rsc)/Rsc)*100 #Percentage increase in scavenging ratio in persent\n",
"\n",
"#Output\n",
"print\"The percentage change in the scavenging ratio = \",round(Rscr,1),\"percent\"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"The percentage change in the scavenging ratio = 66.1 percent\n"
]
}
],
"prompt_number": 1
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.2 page no:367"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Input data\n",
"d=0.12 #The bore diameter of the engine in m\n",
"l=0.15 #The stroke length of the engine in m\n",
"r=16.0 #The compression ratio \n",
"N=2000.0 #The speed of the engine in rpm\n",
"mf=(240/60.0) #Actual air flow per min in kg/min\n",
"T=300.0 #Air inlet temperature in K\n",
"p=1.025 #Exhaust pressure in bar\n",
"R=287 #Real gas constant in J/kg\n",
"\n",
"#Calculations\n",
"import math\n",
"da=(p*10**5)/(R*T)\n",
"Vs=((math.pi)*(d**2)*l)/4.0\n",
"V=(r/(r-1))*Vs\n",
"m=da*V\n",
"m1=m*N\n",
"Rsc=mf/m1 #Scavenging ratio\n",
"nsc=((1-math.exp(-Rsc))*100)\n",
"ntr=((nsc/100.0)/Rsc)*100\n",
"\n",
"#Output\n",
"print\"(a) The scavenging ratio = \",round(Rsc,2)\n",
"print\"(b) The scavenging efficiency = \",round(nsc,1),\"percent \"\n",
"print\"(c) The trapping efficiency = \",round(ntr,1),\" percent\"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"(a) The scavenging ratio = 0.93\n",
"(b) The scavenging efficiency = 60.5 percent \n",
"(c) The trapping efficiency = 65.1 percent\n"
]
}
],
"prompt_number": 4
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.3 page no: 368"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Input data\n",
"mf=6.5 #Mass flow rate of fuel in kg/h\n",
"N=3000.0 #The speed of the engine in rpm\n",
"a=15 #The air fuel ratio\n",
"CV=44000 #The calorific value of the fuel in kJ/kg\n",
"pm=9 #The mean piston speed in m/s\n",
"pmi=4.8 #The mean pressure in bar\n",
"nsc=85 #The scavenging efficiency in percent\n",
"nm=80 #The mechanical efficiency in percent\n",
"R=290.0 #Real gas constant in J/kgK\n",
"p=1.03 #The pressure of the mixture in bar\n",
"T=288.0 #The temperature of the mixture in K\n",
"\n",
"#Calculations\n",
"import math\n",
"ma=a*mf\n",
"L=((pm*60)/(2*N))*100\n",
"mac=mf+ma\n",
"mi=(mac)/(nsc/100.0)\n",
"da=(p*10**5)/(R*T)\n",
"d=(((mi/da)*(4/math.pi)*(1/(L/100.0))*(1/(60*N)))**(1/2.0))*100\n",
"ip=(pmi*10**5*(L/100)*((math.pi/4.0)*(d/100)**2)*N)/(60*1000)\n",
"bp=ip*(nm/100.0)\n",
"nth=(bp/((mf/3600.0)*CV))*100\n",
"\n",
"#Output\n",
"print\"The diameter of the bore = \",round(d,2),\"cm\"\n",
"print\"The length of the stroke = \",L,\" cm\" \n",
"print\"The brake power = \",round(bp,2),\" kW\"\n",
"print\"The brake thermal efficiency =\",round(nth,2),\" percent \"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"The diameter of the bore = 8.83 cm\n",
"The length of the stroke = 9.0 cm\n",
"The brake power = 10.58 kW\n",
"The brake thermal efficiency = 13.32 percent \n"
]
}
],
"prompt_number": 3
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.4 page no: 369"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Input data\n",
"d=0.08 #The diameter of the bore in m\n",
"L=0.1 #The length of the stroke in m\n",
"r=8.0 #The compression ratio \n",
"o=60.0 #The exhaust port open before BDC in degrees\n",
"v=60.0 #The exhaust port closes after BDC in degrees\n",
"a=15.0 #Air fuel ratio \n",
"T=300.0 #The temperature of the mixture entering into the engine in K\n",
"p=1.05 #The pressure in the cylinder at the time of clomath.sing\n",
"R=290.0 #Real gas constant in J/kgK\n",
"ma=150.0 #Mass flow rate of air in kg/h\n",
"N=4000.0 #The speed of the engine in rpm\n",
"\n",
"#Calculations\n",
"import math\n",
"mf=ma/a\n",
"mac=ma+mf\n",
"r=(L*100)/2.0\n",
"Le=(r+(r*math.sin (math.pi/6.0)))/100.0\n",
"Vse=(math.pi*d**2*Le)/4.0\n",
"V=(r/(r-1))*Vse\n",
"V=0.00043 #Value in book after approximation\n",
"da=(p*10**5)/(R*T)\n",
"m=V*da\n",
"mi=m*60*N\n",
"Rsc=mac/mi \n",
"nsc=(1-(exp(-Rsc)))*100\n",
"ntr=nsc/Rsc\n",
"\n",
"#Output\n",
"print\"The scavenging ratio = \",round(Rsc,2)\n",
"print\"The scavenging efficiency =\",round(nsc,2),\" percent \"\n",
"print\"The trapping efficiency = \",round(ntr,2),\"percent\"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"The scavenging ratio = 1.28\n",
"The scavenging efficiency = 72.32 percent \n",
"The trapping efficiency = 56.3 percent\n"
]
}
],
"prompt_number": 18
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.5 page no: 371"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#Input data\n",
"d=8.25 #The diameter of the bore in cm\n",
"L=11.25 #The length of the stroke in cm\n",
"r=8.0 #The compression ratio \n",
"N=2500.0 #The speed of the engine in rpm\n",
"ip=17.0 #Indicated power in kW\n",
"a=0.08 #Fuel air ratio \n",
"T=345.0 #Inlet temperature mixture in K\n",
"p=1.02 #Exhaust pressure in bar\n",
"CV=44000.0 #The calorific value of the fuel in kJ/kg\n",
"nth=0.29 #Indicated thermal efficiency\n",
"M=114.0 #Molar mass of fuel \n",
"R=8314.0 #Universal Gas constant in J/kgK\n",
"\n",
"#Calculations\n",
"import math\n",
"Vs=(math.pi*d**2*L)/4 #Displacement volume in cm**3\n",
"V=(r/(r-1))*Vs #Total cylinder volume in m**3\n",
"ps=((29*p*10**5)/(R*T))*(1/(1+a*(29/M))) #The density of dry air in kg/m**3\n",
"nsc=((ip*1000)/((N/60)*V*10**-6*ps*a*CV*1000*nth))*100 #The scavenging efficiency in percent\n",
"\n",
"#Output\n",
"print\"The scavenging efficiency = \",round(nsc,2),\" percent\"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"The scavenging efficiency = 57.54 percent\n"
]
}
],
"prompt_number": 21
},
{
"cell_type": "heading",
"level": 2,
"metadata": {},
"source": [
"Example 11.6 page no: 372"
]
},
{
"cell_type": "code",
"collapsed": false,
"input": [
"#given\n",
"S=15.0 #The speed of the math.piston in m/s\n",
"ps=0.35 #The scavenging pressure in bar\n",
"pa=1.03 #Atmospheric pressure in bar\n",
"r=18.0 #The compression ratio \n",
"t=35.0 #The inlet temperature in degree centigrade\n",
"Rsc=0.9 #The scavenging ratio \n",
"ta=15.0 #The atmospheric temperature in degree centigrade\n",
"nc=0.75 #Compressor efficiency \n",
"g=1.4 #Adiabatic index\n",
"R=287.0 #Real gas constant in J/kgK\n",
"Cp=1005.0 #Specific heat of gas in J/kgK\n",
"\n",
"#Calculations\n",
"import math\n",
"pi=ps+pa #The scavenging pressure in bar\n",
"Ti=(273+ta)+t #The inlet temperature in K\n",
"pr=pa/math.pi #The ratio of the pressure for calculations\n",
"di=(pi*10**5)/(R*Ti) #The density in kg/m**3\n",
"ai=(g*R*Ti)**(1/2.0) #The sonic velocity in m/s\n",
"C=(Rsc)/(2*((r-1)/r)*(ai/S)*(pi/pa)*((2/(g-1))*(((pr)**(2/g))-((pr)**((g+1)/g))))**(1/2.0))\n",
"ds=(pa*10**5)/(R*Ti) #The density in kg/m**3\n",
"mep=(ds*Rsc*Cp*Ti*(((pi/pa)**((g-1)/g))-1))/((nc*((r-1)/r))*10**5) #Mean effective pressure in bar\n",
"\n",
"#Output\n",
"print\"The flow coefficient = \",round(C,3) \n",
"print\"The compressor mean effective pressure = \",round(mep,1),\"bar\"\n"
],
"language": "python",
"metadata": {},
"outputs": [
{
"output_type": "stream",
"stream": "stdout",
"text": [
"The flow coefficient = 0.028\n",
"The compressor mean effective pressure = 0.4 bar\n"
]
}
],
"prompt_number": 33
}
],
"metadata": {}
}
]
}