Hands-On: Engine Plant Model

#!/usr/bin/env python3
# Mean-value engine model: torque and speed dynamics
# 4-cylinder 2.0L petrol; 1 ms step rate

import numpy as np

class MeanValueEngine:
    def __init__(self):
        self.omega_e  = 800 * 2*np.pi/60  # idle (rad/s)
        self.T_coolant= 20.0               # coolant temp (C)
        self.J_engine = 0.3                # rotational inertia (kg.m2)

    def step(self, throttle_pct, load_torque_Nm, dt):
        rpm = self.omega_e * 60 / (2*np.pi)

        eta_vol = 0.85 * (1 - 0.1*np.cos(rpm/1000)) * (throttle_pct/100)
        eta_vol = np.clip(eta_vol, 0.0, 1.0)

        BMEP = 1.2e6 * eta_vol * (throttle_pct/100)
        T_indicated = BMEP * 2.0e-3 / (4*np.pi)  # 2.0L displacement
        T_friction   = 15 + 0.01*rpm

        T_net = T_indicated - T_friction - load_torque_Nm
        self.omega_e += (T_net / self.J_engine) * dt
        self.omega_e  = max(self.omega_e, 0.0)

        T_eq = 90 + 10*(throttle_pct/100)
        self.T_coolant += (T_eq - self.T_coolant) / 300 * dt

        return {
            "rpm":         self.omega_e * 60/(2*np.pi),
            "torque_Nm":   T_indicated - T_friction,
            "map_kPa":     30 + 70*(throttle_pct/100),
            "coolant_degC":self.T_coolant,
        }