""" Two stroke squish velocity calculator Based on G.P. Blair's method ("Design and Simulation of Two-Stroke Engines", 1996, p. 325-330) Copyright 2017 Elmeri Laakkonen Licensed under GNU GPLv3 """ from math import * from tkinter import * import tkinter.messagebox as mb import matplotlib matplotlib.use("TkAgg") import matplotlib.pyplot as plt GAS_R = 287.058 GAMMA = 1.401 class SquishVelocityCalculator: def __init__(self): self.__window = Tk() self.__window.title("Squish velocity calculator") Label(self.__window, text="Squish velocity calculator").grid(row=0, columnspan=5) Label(self.__window, text="Input data below").grid(row=1, columnspan=5) Label(self.__window, text="Bore (mm):").grid(row=2, column=0, sticky=W, padx=15) Label(self.__window, text="Stroke (mm):").grid(row=3, column=0, sticky=W, padx=15) Label(self.__window, text="Conrod length (mm):").grid(row=4, column=0, sticky=W, padx=15) Label(self.__window, text="RPM:").grid(row=5, column=0, sticky=W, padx=15) Label(self.__window, text="Exhaust timing (deg ATDC):").grid(row=6, column=0, sticky=W, padx=15) Label(self.__window, text="Compression ratio:").grid(row=7, column=0, sticky=W, padx=15) Label(self.__window, text="Squish area ratio (%):").grid(row=8, column=0, sticky=W, padx=15) Label(self.__window, text="Squish angle (deg):").grid(row=9, column=0, sticky=W, padx=15) Label(self.__window, text="Squish clearance (mm):").grid(row=10, column=0, sticky=W, padx=15) self.bore_entry = Entry(self.__window) self.bore_entry.grid(row=2,column=3,sticky=E, padx=15) self.stroke_entry = Entry(self.__window) self.stroke_entry.grid(row=3,column=3,sticky=E, padx=15) self.conrod_entry = Entry(self.__window) self.conrod_entry.grid(row=4,column=3,sticky=E, padx=15) self.rpm_entry = Entry(self.__window) self.rpm_entry.grid(row=5,column=3,sticky=E, padx=15) self.exh_timingEntry = Entry(self.__window) self.exh_timingEntry.grid(row=6,column=3,sticky=E, padx=15) self.cr_entry = Entry(self.__window) self.cr_entry.grid(row=7,column=3,sticky=E, padx=15) self.sqarea_entry = Entry(self.__window) self.sqarea_entry.grid(row=8,column=3,sticky=E, padx=15) self.sqangle_entry = Entry(self.__window) self.sqangle_entry.grid(row=9,column=3,sticky=E, padx=15) self.sqclearance_entry = Entry(self.__window) self.sqclearance_entry.grid(row=10,column=3,sticky=E, padx=15) self.calc_button = Button(self.__window, text="Calculate", command=self.initialize) self.calc_button.grid(row=11,column=3,sticky=E, padx=15, pady=15) self.read_data() # Initial values / placeholders self.sum_energy = 0 self.crank_angle = [] self.sqv_array = [] self.kinetic_energy_array = [] self.pressure_max = 0 self.max_sqv = 0 self.max_deg = 0 self.bore = 0.00 self.stroke = 0.00 self.conrod = 0.00 self.rpm = 0.00 self.exh_timing = 0.00 self.cr = 0.00 self.sqarea_ratio = 0.00 self.sqangle = 0.00 self.sqclearance = 0.00 self.boreMeters = self.bore / 1000 self.strokeMeters = self.stroke / 1000 self.conrodMeters = self.conrod / 1000 self.crank = self.stroke / 2 self.crankMeters = self.crank / 1000 self.squish_clearance_meters = self.sqclearance / 1000 self.piston_area = pi * (self.boreMeters ** 2) / 4 self.swept_volume = self.piston_area * self.strokeMeters def initialize(self): try: self.bore = float(self.bore_entry.get()) self.stroke = float(self.stroke_entry.get()) self.conrod = float(self.conrod_entry.get()) self.rpm = float(self.rpm_entry.get()) self.exh_timing = float(self.exh_timingEntry.get()) self.cr = float(self.cr_entry.get()) self.sqarea_ratio = float(self.sqarea_entry.get())/100 self.sqangle = float(self.sqangle_entry.get()) self.sqclearance = float(self.sqclearance_entry.get()) self.boreMeters = self.bore/1000 self.strokeMeters = self.stroke/1000 self.conrodMeters = self.conrod/1000 self.crank = self.stroke/2 self.crankMeters = self.crank/1000 self.squish_clearance_meters = self.sqclearance/1000 self.piston_area = pi*(self.boreMeters**2)/4 self.swept_volume = self.piston_area*self.strokeMeters self.save_info() self.calculate() except: mb.askretrycancel("Error", "Input numerical values only.", icon=mb.ERROR, type="ok") def save_info(self): infostring = "{};{};{};{};{};{};{};{};{}".format( self.bore, self.stroke, self.conrod, self.rpm, self.exh_timing, self.cr, self.sqarea_ratio*100, self.sqangle, self.sqclearance ) try: filehandle = open('data.txt', 'w') filehandle.write(infostring) except IOError: # couldn't write data.txt mb.showerror('Error', 'Couldn\'t write data.txt') def piston_position(self, crank_angle): CT = self.strokeMeters / 2 alpha = degrees(asin(CT * sin(radians(crank_angle)) / self.conrodMeters)) x = self.conrodMeters + CT - cos(radians(alpha)) * self.conrodMeters - cos(radians(crank_angle)) * CT return x def calculate(self): height_exh_open_meters1 = self.piston_position(self.exh_timing) trapped_swept_volume = self.piston_area*height_exh_open_meters1 clearance_volume = trapped_swept_volume/(self.cr-1) squish_perpendicular_area = self.sqarea_ratio*self.piston_area bowl_area = self.piston_area-squish_perpendicular_area bowl_diam = sqrt(4*bowl_area/pi) squish_radial_radius = (self.boreMeters-bowl_diam)/2 squish_cone_height = tan(radians(self.sqangle))*squish_radial_radius squish_cone_volume = 1/3*pi*squish_radial_radius**2*squish_cone_height squish_bowl_volume = self.squish_clearance_meters*bowl_area squish_band_volume = self.squish_clearance_meters*squish_perpendicular_area if self.sqangle > 0: squish_band_volume += squish_cone_volume bowl_volume = clearance_volume-squish_band_volume-squish_bowl_volume vol_squish1 = height_exh_open_meters1*squish_perpendicular_area+squish_band_volume vol_bowl1 = height_exh_open_meters1*bowl_area+bowl_volume+squish_bowl_volume vol_cyl1 = height_exh_open_meters1*self.piston_area+clearance_volume trapped_vol = vol_cyl1 pressure_trap = 101325 temp_trap = 293 mass_trapped = pressure_trap * trapped_vol / (GAS_R * temp_trap) pressure_cyl1 = pressure_trap pressure_squish1 = pressure_cyl1 pressure_bowl1 = pressure_cyl1 mass_squish1 = mass_trapped * vol_squish1 / vol_cyl1 degree_step = 1 # step dt = degree_step / (6 * self.rpm) # delta t angleDown = (360 - self.exh_timing) while angleDown <= 360: height_exh_open_meters2 = self.piston_position(angleDown) dh = height_exh_open_meters1 - height_exh_open_meters2 vol_squish2 = height_exh_open_meters2 * squish_perpendicular_area + squish_band_volume vol_bowl2 = height_exh_open_meters2 * bowl_area + squish_bowl_volume + bowl_volume vol_cyl2 = height_exh_open_meters2 * self.piston_area + clearance_volume pressure_cyl2 = pressure_trap * (pressure_trap / vol_cyl2) ** GAMMA temp_cyl2 = pressure_cyl2 * vol_cyl2 / (mass_trapped * GAS_R) rho_cyl2 = pressure_cyl2 / (GAS_R * temp_cyl2) pressure_squish2 = pressure_squish1 * (vol_squish1 / vol_squish2) ** GAMMA pressure_bowl2 = pressure_bowl1 * (vol_bowl1 / vol_bowl2) ** GAMMA mass_squish2 = mass_trapped * vol_squish2 / vol_cyl2 delms = mass_squish1 - mass_squish2 hsq = height_exh_open_meters1 + self.squish_clearance_meters - 0.5 * dh if self.sqangle >= 0: hsq += squish_cone_height sql = pi * bowl_diam asv = hsq * sql sqv = delms / (rho_cyl2 * asv * dt) self.sqv_array.append(sqv) self.crank_angle.append(360 - angleDown) if sqv > self.max_sqv: self.max_sqv = sqv self.max_deg = 360 - angleDown pressure_ratio = pressure_squish2 / pressure_bowl2 if pressure_ratio > self.pressure_max: self.pressure_max = pressure_ratio kinetic_energy = 0.5 * delms * sqv ** 2 self.sum_energy += kinetic_energy self.kinetic_energy_array.append(kinetic_energy) height_exh_open_meters1 = height_exh_open_meters2 vol_squish1 = vol_squish2 vol_bowl1 = vol_bowl2 mass_squish1 = mass_squish2 pressure_squish1 = pressure_cyl2 pressure_bowl1 = pressure_cyl2 angleDown = angleDown + degree_step self.plot() def plot(self): fig = plt.figure(0) plt.plot(self.crank_angle, self.sqv_array, 'r-') plt.xlabel('Crankshaft angle (deg BTDC)') plt.ylabel('Velocity (m/s)') plt.title('Squish velocity') plt.grid(True) plt.text(2, 2, 'Max sq. v: {:.2f}m/s @{:.2f} deg BTDC'.format(self.max_sqv, self.max_deg)) plt.text(2, 1, "Max squish pressure ratio: {:.4f}".format(self.pressure_max)) plt.text(2, 0, "Total kinetic energy squished: {:.2f}mJ".format(self.sum_energy * 1000)) fig.canvas.set_window_title('Squish velocity') plt.show() def read_data(self): try: filehandle = open('data.txt', 'r') data_string = filehandle.read() except IOError: # couldn't read data.txt data_string = "" if len(data_string) > 0: data = data_string.split(";") self.bore_entry.insert(0, data[0]) self.stroke_entry.insert(0, data[1]) self.conrod_entry.insert(0, data[2]) self.rpm_entry.insert(0, data[3]) self.exh_timingEntry.insert(0, data[4]) self.cr_entry.insert(0, data[5]) self.sqarea_entry.insert(0, data[6]) self.sqangle_entry.insert(0, data[7]) self.sqclearance_entry.insert(0, data[8]) def start(self): self.__window.mainloop() ui = SquishVelocityCalculator() ui.start()