# Diesel Engine driving a generator

1. Aug 28, 2009

### talaroue

1. The problem statement, all variables and given/known data

A diesel engine which drives a generator has an output of 60 hp operating at a n=31%. Then generator has a n=79% and supploes a load circuit at 240 V. The diesel engine uses light fuel oil (LFO) with a calorific value of 19,600 BTU/lb.
Calculate:
1. The generator output in kW
2. The current in the generator
3. the fuel consumption in gallons per day

(weight of LFO=8.3lb/gal; 1BTU=1055J)

2. Relevant equations
P=IV

3. The attempt at a solution
I am not sure if this is correct, its out of the book so I don't know.

For the first part i simple turned the 60hp into W knowing that 1 hp=745.7 W, so that gave me 44,742 W. I then multiplied that number by .79(the effecicency of the generator to get 35,346.2W which is equal to 35.35 kW. Is this correct?

For the second part I simpled used P=IV plugging in P=35.35kW, and V=240 to get 147.27 A. I believe this part is right aslong as the first part is right.

The third and final part i used what I learned in chemistry, stochiometry in a way,

35,346.2 W *(1 BTU/1055 W)*(1 lb/19,600 BTU)*(1 gal/8.3 lb)=2.06x10^-4 gals

everything except gals cancels, but the question asks gals/day but i don't know how I would do that....

Thanks for your help!

2. Aug 28, 2009

### talaroue

any ideas?

3. Aug 28, 2009

### talaroue

I am just confusing myself more and more.

4. Aug 28, 2009

### talaroue

Why can't I understand circuits :-/ thank god my major is Civil.

5. Aug 29, 2009

### OmCheeto

In your equation: 35,346.2 W *(1 BTU/1055 W)*(1 lb/19,600 BTU)*(1 gal/8.3 lb)=2.06x10^-4 gals

Where did (1 BTU/1055 W) come from?

6. Aug 29, 2009

### RTW69

Your diesel engine puts out 60 hp but it is only 31% efficient. Therefore the input energy to the engine is 193.5 hp. That is the energy the oil must supply to get 60 hp output.

1 hp=33475 btu/hr, 1 lb of oil provides 19,600 btu's, 1 gal of LFO weighs 8.3 lb, there are 24 hours in a day (assuming the engine 24 hours)

This information will give you gallons of LFO used per day

7. Aug 29, 2009

### talaroue

RTW69: Where did you find that 1 hp=33475 btu/hr?

OmCheeto: I thought that it said 1 BTU/1055J but really it said 1 BTU=1055 J so I could just multiple change for BTU to J just by multipling. I think I am going to go with RTW69 said and see where that takes me.

8. Aug 29, 2009

### talaroue

Were my other parts correct for this problem then?

9. Aug 29, 2009

### OmCheeto

It is the same thing in the context of your equation.
Yes. But you converted 1 BTU = 1055 J to 1 BTU = 1055 W.
1 Joule does not equal 1 Watt.
My conversion table says 1 hp = 42.4 btu/min, which does not yield 33475 btu/hr.

10. Aug 29, 2009

### talaroue

I think I was wrong before can someone tell me if I am right now? (i am making another post right now)

11. Aug 29, 2009

### talaroue

Part A: The generator output in kW

If the engine has a input of 193.55 hp that means the output of the generator has to be 193.55 correct? so then I just do 193.55*745.7 W/1000=144.33 kW?

Part B: The current in the gnerator load ciruit

If the generator has an output of 193.55 with a effeicency of 79% the input is 245 hp, so then I use P=VI solve for I=P/V I have 245 hp*745.7W/240 V=761.24 Amps

Part C: The fuel consumption

193.55hp*(33475BTU/hr)*(1 lb/ 19,600 BTU)* (1 gal/8.3 lb)*(24 hr/1 day)=955.85 gal/day

12. Aug 29, 2009

### talaroue

or instead of the 193.55 hp should it be the input of the generator which is 245 hp?

13. Aug 29, 2009

### OmCheeto

No. The initial problem stated:
ie. the output of the diesel engine is 60 hp.

The output of the generator will be less since it is only operating at 79% efficiency.

14. Aug 29, 2009

### RTW69

1 Boiler horsepower (Bohp)=33,475 Btu/hr. It is a term used to rate boilers and is the energy needed to evaporate 34.5 lbs of water at 212 degrees F in one hour. You should probably use electric horsepower instead. I electric horsepower is 746 watts. 1 watt is 3.4129 Btu/hr or 1 electric horsepower is 2545 btu/hr. Sorry for the confusion.

15. Aug 30, 2009

### talaroue

The output of the engine=the input of the generator? is this correct

16. Aug 30, 2009

### talaroue

When I find the current in the generator load circuit do I use the power output? or input?

17. Aug 30, 2009

### OmCheeto

Yes

Output

18. Aug 30, 2009

### talaroue

Ok, and why is that?

19. Aug 30, 2009

### OmCheeto

Why what? Yes or output?

20. Aug 31, 2009

### talaroue

Why is it the output? Sorry about that