Solving a non linear coupled system of ODE

i have that system and i made my code

clear all

close all

clc

ti = [0 0.0799 0.0809 0.0819 0.0829 0.0839 0.0849 0.0859 0.0869 0.0879 0.0889 0.0899 ]';

uu = [0 29.541444 150.99871 279.94913 416.61618 561.22227 713.98823 875.13276 1044.8719 1223.4184 1410.981 ]';

spl = pchip(ti,uu);

T=1;

[t,x]= ode45(@batch,[0 T],[0 0 ppval(spl,0)]);

figure(1)

plot(t,x(:,1),t,x(:,2))

figure(2)

plot(t,x(:,3))

the function batch is the following :

function dx=batch(t,x)

Mp=0.4;

Ap=0.00628;

Patm=101325;

Kp=242640;

Xpo=1.5928*10^(-3);

rou=880;

Cd=0.7;

Aorifice=2.0442*(10^(-5));

Vo=7.8*(10^(-5));

Beta=1625*(10^5);

Dp=135.4;

ti = [0 0.0799 0.0809 0.0819 0.0829 0.0839 0.0849 0.0859 0.0869 0.0879 0.0889 0.0899 ]';

uu = [0 29.541444 150.99871 279.94913 416.61618 561.22227 713.98823 875.13276 1044.8719 1223.4184 1410.981 1]';

spl = pchip(ti,uu);

dx=zeros(3,1);

dx(1)=x(2);

dx(2)=(1/Mp)*(Ap*(x(3)-Patm)-Kp*(x(1)+Xpo)-(Dp*x(2)));

dx(3)=(Beta/(Vo+(Ap*x(1))))*(Cd*Aorifice*sqrt(2*((ppval(spl,t)-x(3)))/rou)-(Ap*x(2)));

end

but i found oscillation in the beginnig (unexpected) , ken someone find why ?