IC engine plot graph

can someone help with this code, I tried to change the variable N speed from 2000:2000:12000 and it seems that my graphs were still constant with 2000 rpm?

% Engine parameters
r = 10.5;        % compression ratio
b = 0.077;              % bore [m]
s = 0.0858;             % stroke [m]
cr = 0.1365;            % connecting rod length [m]
ct = s/2;               % crank throw [m]
Vd = 0.0016/4;%0.25*pi*s*b^2;     % displacement volume [m3]
V2 = Vd./(r-1);          % TDC volume [m3]
V1 = r.*V2;              % BDC volume [m3]
N = [2000:2000:12000]*(1/60);        % engine speed [rev/s]

% Chemical parameters
LHV = 42000000;         % lower heating value of gasoline [J/kg]
FA = 14.7;              % stoichiometric air/fuel ratio
g = 1.4;              % ratio of specific heats - unburned
R = 287;                % particular gas constant [J/kgK]   
cv = R/(g-1);               % constant-volume specific heat at high temps [J/kg-K]

% Cycle parameters
CAD = 0:1:720;
CADrad = CAD*pi/180;
% Displacement and volume
y = cr+ct-(sqrt(cr.^2 - (ct.^2).*sin(CADrad).^2)+ct.*cos(CADrad));
V = V2 + 0.25.*pi.*(b.^2).*y;

% Supercharger calculation
etac = 1;                           % supercharger component efficiency
cps = 1001;                         % cp of supercharger [J/kg-K] (at a low temp)
PR = 1;                           % supercharger pressure ratio
Patm = 101325;                      % atmospheric pressure [Pa]
Tatm = 300;                         % atmospheric temperature [K]

% Cycle calculation
CADc = 180:1:540;                   % crank angles of compression and expansion strokes
Vc = V(179:539);                    % volumes during compression and expansion strokes [m3]
M = zeros(size(N));                % charge mass [kg]
Mf = zeros(size(N));                % mass of fuel [kg]
Qin = zeros(size(N));               % heat addition [kg]
P = zeros(length(N),length(Vc));   % pressures [Pa]
T = zeros(length(N),length(Vc));   % temperatures [K]
Wcycle = zeros(1,length(N));       % cycle power for 4 cylinders [W]
mdot = zeros(1,length(N));         % mass flow into engine for 4 cylinders [kg]
Ws = zeros(size(N));               % power of the supercharger [W]
Wnet = zeros(1,length(N));         % net power including supercharger for 4 cylinders [W]
eta = zeros(size(N));              % thermal efficiency
    
for count = 1:length(N)
    % supercharger
    P1 = PR*Patm;                       % intake runner pressure [Pa]
    T1s = Tatm*(PR)^((g-1)/g);          % ideal intake runner temperature [K]
    T1 = Tatm - ((Tatm-T1s)/etac);      % real intake runner temperature

    % intake conditions
    P(count,1) = P1;          % intake pressure [Pa]
    T(count,1) = T1;             % intake temperature [K]
    M(count) = P(count,1)*Vc(1)/(R*T(count,1));       % charge mass (fuel + air) [kg]

    % compression stroke
    for count1 = 2:length(CADc(1:181))
        P(count,count1) = P(count,count1-1)*(Vc(count1-1)/Vc(count1))^g;
        T(count,count1) = P(count,count1)*Vc(count1)/(M(count)*R);
    end

    % heat addition - happens from 359-360 CAD
    Mf(count) = M(count)/(1+FA);                  % mass of fuel [kg]
    Qin(count) = Mf(count)*LHV;                   % heat in due to fuel, assuming ideal combustion [J]
    T(count,182) = T(count,181) + Qin(count)/(M(count)*cv);   % temperature from first law [K]
    P(count,182) = M(count)*R*T(count,182)/Vc(182);    % pressure [Pa]

    % explansion stroke
    for count2 = 183:length(CADc)
        P(count,count2) = P(count,count2-1)*(Vc(count2-1)/Vc(count2))^g;
        T(count,count2) = P(count,count2)*Vc(count2)/(M(count)*R);
    end
    
    Wcycle(count) = 2.*N(count).*trapz(Vc,P(count,:));    % power from 4 cylinders - 2 power strokes per revolution of the engine[W]
    mdot(count) = 2.*M(count).*N(count);                          % mass flow rate for 4 cylinders - 2 intake strokes per revoluation [kg/s]
    Ws(count) = -mdot(count).*cps.*(T1-Tatm);            % power from supercharger [W]
    Wnet(count) = Wcycle(count) + Ws(count);             % net power [W]
    eta(count) = Wnet(count)./(2.*Qin(count)*N(count));                  % thermal efficiency with two combustion processes per revolution

end

figure
axes('FontSize',14)
hold on
plot(Vc,P,'LineWidth',2)
grid on
legend('No supercharger','Supercharger')
xlabel('Volume [m^3]')
ylabel('Pressure [Pa]')


figure
axes('FontSize',14)
hold on
plot(N,Wnet*2/N,'-o','LineWidth',2)
grid on
xlabel('Supercharger Pressure Ratio')
ylabel('Net Work [J]')

figure
axes('FontSize',14)
hold on
plot(N,eta,'-o','LineWidth',2)
grid on
xlabel('Supercharger Pressure Ratio')
ylabel('Thermal Efficiency')

Answer 1

[Walter Roberson]

plot(N,Wnet*2/N,'-o','LineWidth',2)

Wnet and N are both vectors, so you have accidentally invoked matrix division. You need

plot(N,Wnet.*2./N,'-o','LineWidth',2)

However you will still see a straight line. If you look at the way you construct Wnet, you have the sum of two values, with each of the values being a multiple of N, so the N potentially factors out when you do the Wnet ./ N