FluidSimCpp/include/FluidSim/Engine.hpp

#pragma once

#include "FluidSim/Component.hpp"
#include "FluidSim/Constants.hpp"
#include <array>
#include <cstddef>
#include <limits>
#include <optional>
#include <random>
#include <vector>

namespace fluidsim::port {

class Ecu;

struct CrankshaftConfig {
    float inertia{0.2f};
    float friction_constant{}, friction_viscous{};
    float friction_quadratic{}; // Nm / (rad/s)^2, dissipative windage term
};

class Crankshaft : public CrankshaftConfig {
public:
    float omega{400.0f * 2.0f * pi / 60.0f};
    float angle{}, previous_angle{};
    float load_torque{}, drivetrain_torque{};
    float average_power{}, average_torque{};

    void add_torque(float torque);
    float take_torque(); // Consume gas torque when an external shaft integrator owns motion.
    void record_output(float torque,float power);
    void step(float dt);
private:
    float external_torque_{};
    std::array<float, 16384> power_buffer_{}, torque_buffer_{};
    std::size_t power_index_{}, power_count_{}, torque_index_{}, torque_count_{};
    float power_sum_{}, torque_sum_{};
};

struct CylinderConfig {
    float bore{0.075f}, stroke{0.068f}, rod{0.112f}, compression{11.5f};
    float intake_valve_diameter{0.030f}, exhaust_valve_diameter{0.028f};
    int intake_valve_count{1}, exhaust_valve_count{1};
    float spark_advance{20.0f}, wiebe_a{5.0f}, wiebe_m{2.0f}, burn_duration{60.0f}, burn_start{5.0f};
    float afr{14.7f}, fuel_lhv{44.0e6f}, energy_variation{0.05f}, misfire_probability{};
    float wall_area{0.02f}, heat_transfer{100.0f}, ambient_temperature{300.0f};
};

class EngineCylinder : public Component, public CylinderConfig {
public:
    Ecu* ecu{};
    bool transported_fuel{};
    float phase{};
    bool rev_limit_enabled{};
    float rev_limit_rpm{7500.0f}, rev_limit_cut_time{0.05f}, rev_limit_hysteresis{200.0f};
    float air_mass{}, exhaust_mass{}, energy{}, volume{}, pressure{101325.0f};
    float fuel_mass{}, burn_fraction{};
    float fuel_equivalent_mass{}; // passive fuel-origin tracer, unaffected by combustion
    bool combustion_active{}, fuel_injected{}, rev_limit_active{};
    Port intake{}, exhaust{};

    std::vector<Port*> ports() override { return {&intake, &exhaust}; }
    float swept_volume() const;
    float clearance_volume() const;
    float total_mass() const;
    float temperature() const;
    float air_fraction() const;
    float compute_volume(float theta) const;
    void initialize(const Crankshaft& crank);
    virtual float valve_area(float cycle_degrees, bool inlet) const = 0;
    virtual void pre_step(Crankshaft& crank, float dt, float throttle) = 0;
    void update_state(float dt) override;

protected:
    float energy_factor_{1.0f};
    float active_fuel_mass_{};
    float rev_limit_timer_{};
    std::mt19937 random_{0xF17D51u};
    std::uniform_real_distribution<float> unit_{0.0f, 1.0f};

    float random_unit();
    static float wrap_degrees(float value, float cycle_degrees = 720.0f);
    static bool crossed_angle(float previous, float current, float event) {
        return current >= previous ? previous < event && current >= event : event > previous || event <= current;
    }
    void update_rev_limiter(float rpm, float dt);
    void sync_ports();
};

class FourStrokeCylinder final : public EngineCylinder {
public:
    struct IgnitionCommand {bool fire{},cut{true};};
    // Present selects external timing exclusively. A fire pulse is consumed
    // once; missing subsequent commands cannot recreate internal timed sparks.
    // Requires physically transported fuel, including carburetor operation.
    std::optional<IgnitionCommand> ignition_command;
    // Once per cycle, before ignition consumes fuel. Independent of spark cut.
    float charge_afr{std::numeric_limits<float>::quiet_NaN()};
    bool charge_sampled{};
    struct CamPoint { float angle_degrees{}, lift_metres{}; };
    struct ValveDynamics {
        float mass_kg{0.035f};
        float spring_rate_n_per_m{30000.f};
        float damping_n_s_per_m{24.f};
        float seat_force_n{100.f};
        float maximum_lift_m{0.015f};
        float seat_restitution{0.005f}, cam_restitution{0.01f}, stop_restitution{0.01f};
    };
    struct CamProfile { std::vector<CamPoint> points; };

    void set_valve_profiles(const CamProfile& intake_cam, const ValveDynamics& intake_valve,
                            const CamProfile& exhaust_cam, const ValveDynamics& exhaust_valve);
    float valve_area(float cycle_degrees, bool inlet) const override;
    void pre_step(Crankshaft& crank, float dt, float throttle) override;
    float take_contact_impulse() { const float value=contact_impulse_;contact_impulse_=0;return value; }
    bool valve_floating() const { return intake_floating_ || exhaust_floating_; }
    float intake_lift() const { return intake_lift_; }
    float exhaust_lift() const { return exhaust_lift_; }
    static float cam_lift_at(const CamProfile& profile,float degrees) { return sample_cam(profile,degrees).lift_metres; }

private:
    float external_burn_angle_{};
    bool external_charge_ready_{};
    struct ValveState { float lift{},velocity{};bool floating{}; };
    const CamProfile* intake_cam_{};
    const CamProfile* exhaust_cam_{};
    ValveDynamics intake_dynamics_{},exhaust_dynamics_{};
    ValveState intake_state_{},exhaust_state_{};
    float intake_lift_{},exhaust_lift_{},contact_impulse_{};
    bool intake_floating_{},exhaust_floating_{};

    static CamPoint sample_cam(const CamProfile& profile,float degrees);
    float advance_valve(ValveState& state,const CamProfile& cam,const ValveDynamics& dynamics,
                        bool inlet,const Crankshaft& crank,float dt);
};
} // namespace fluidsim::port