Terry, I have some questions about your calculator:
1. What is meant by "Propane price calculated as a percentage of gasoline"?
2. The only fields that seem to affect the numbers are number of hours per year, number of gallons per year and obviously the two price per gallon fields. So are those other fields necessary?
3. The fuel cost results are simple enough, but I noticed you've specified the same fuel burn rate for both the gasoline and propane. Is this the case? Could I expect to burn one gallon per hour with propane if I burn one gallon per hour with gasoline?
4. How do you arrive at your fuel control cost?
5. Is the maintenance cost figured as a recurring yearly cost, or is it a total lifetime of the equipment cost divided over the expected number of years the equipment will be in service?
Now that you can see my questions, here is a list in order of what is in my mind in regards to these questions. My intent is for you to see what I'm thinking so you can better explain the answers.
1. This one, I haven't got a clue other than around here, right now, propane is 67% the cost of gasoline. Obviously that is not what this field is looking for.
2. I'm thinking no.
3. I realize propane is used as a vapor, but both gasoline and propane are bought and stored in a liquid form, therefore the comparisons are stated in "per gallon." If propane has fewer BTU's per gallon than gasoline, how can it achieve the same burn rate for similar power output? Remember, we're talking lawnmower engines, not specially modified engines that operate more efficiently on propane.
4. This appears to be calculated at 10% of total fuel cost. Maybe this is a commercial operator cost, but as a homeowner, I don't spend that much per year. Infact, I may only spend $5-$10 per year replacing an occasional gas can every other year.
5. If this is just regular engine maintenance costs, I don't spend but one third of what the calculator is showing.
Like I've said before, you've got a neat little calculator there. I've followed this thread, and at times, it has gotten rather interesting to say the least. I am old enough to remember all the conversions done on daily driver cars/trucks in the late 70's, and also that they faded away almost as soon as the 80's rolled around. Other than the Schwan's trucks in this area, we don't have any fleet vehicles running propane. I know vehicle technology has advanced since the 70's, and engines are far more efficient in general and are running higher compression ratios, but I have to ask myself why aren't there more propane powered vehicles on the road if it was cost effective? I know this has been debated in length here, and that was purely an observation and I'm not looking specifically for a reply to that question.
However, I would like to see this thread brought back on track.