rec.autos.simulators

I hope this is the right newsgroup for this question, otherwise please
direct me to the correct one. My math and my knowledge of car mechanics
range from rusty to inexistent, I hope you can still bear with me.

Having said that: I am trying to set up a very simplicistic car
simulation. My first step looks basically like this:

// time frame in s, applied thrust in N
public void step(double time,double thrust) {
  double force=thrust-getResistance(); // rolling and air resistance
  double acceleration=force/weight;
  velocity+=acceleration*time;
  position+=velocity*time;

That seems to work. Now I would like to specify the amount of fuel burnt
in the given time frame instead of applied thrust. (I assume that I get
the whole fuel energy without any loss for the moment.) But I have
problems figuring out how to calculate the resulting thrust force from
the fuel energy.

I think I need the distance traveled in this time frame, however, this
value is not available at the moment I'm calculating thrust. Am I
totally on the wrong track? Could somebody please enlighten me or point
me to a decent web page on this topic?

Regards,
Patrick

You can't go exactly from rate of fuel consumed (g/s or kW or
similar) to thrust, but you can go from fuel to power if you know
the efficiency of the engine.  Efficiency (or brake specific fuel
consumption) is often plotted as a fcn of torque and rpm, but you
can start with a number like 30% if you wish (varies from about
20-35 or 40% depending on load, rpm, engine technology).

Anyway, in power units:
fuel consumed (power)*efficiency = engine power = torque (engine)*
rpm
torque (wheel) = gear ratio * torque (engine) * drivetrain
efficiency
road force = torque(wheel)*wheel efficiency/radius

Regards,
Patrick

Regards,
Patrick

Best regards,
Patrick

I ready every post and reply, and tried to follow what was happening, but
got a nose bleeed from the mental extertion.

Hope you find a simple solution - but I'd hate to see the complex version!

Keith

I believe the theoretically perfect thermodynamic engine operating
between peak cumbustion temperature and ambient temperature is capable
of about 20% efficiency.  Real engines are less efficient than that.

Later,
Jason C. Wells

Regards,
Patrick

Nah, gasoline ICE's peak efficiencies are in the 35% range.  
That's usually at mid rpm and high (but not full) throttle.  
Overall average efficiency over a typical drive cycle
(city/highway) is about 20-25%.  That's defined as engine net
crank power over fuel energy (lower heating value).  Diesels peak
out at about 40%, sometimes a couple of points higher.  And I
believe they don't drop off as much as gasoline engines do at
lower throttle settings.

Real would be less, which means you are closer than I am.  Patrick, use
  Dave's number.

Later,
Jason C. Wells

Regards,
Patrick