How would I be able to experimentally test the efficiency of conventional and alternate sources of car fuel?

Question

We are trying to determine the efficiency of unleaded gasoline, pure ethanol, 10% ethanol, B20, and B100 (using Jatropha biofuel). Most likely, we will try to use a basic self built calorimeter to test for how long the fuels burn, how quickly they reach their maximum heat (and what that maximum heat is), the time it takes to reach its flash point, and the overall heat/energy produced. How should we go about with this experiment? How could we build our own calorimeter? How much fuel should we be burning (we were thinking about 250ml but that might be a bit dangerous...)? Are there any other important sources of fuel that we should be including in our tests? We also wanted to try and test for the negative emissions, but that might be hard. Do you have any idea of how we could measure these emissions (CO2, nitrogen, sulfur, etc)?

Answer 1

There is a slight problem with the comparison of "apples and oranges." Gasoline and diesel fuels are used under different conditions and will give different results. The products of combustion will also change as a function of pressure.

The reactions of burning a fuel with atmospheric gases can be very different than exploding the same fuel under pressure.

In a bomb calorimeter, very small samples (under 1.0 mL) could be used. The oxygen content might be a problem unless STP was used for all specimens. Flash point is measurable but time studies are almost impossible.

A realistic approach might be to use an actual engine with carburetion or fuel injection modification for the different fuels (at least the gasoline variety). The total torqued rpm could be measured. If the engine was located in a vehicle, the distance traveled could be measured. The exhaust gases could be analyzed with typical gas chromatography techniques.

Several additional biodiesel fuels are currently available. Methane might be one addition. There are several biosources. You might also want to look at Methanol and not just Ethanol for the alcohols.

Answer 2

Don't waste your money on a self built calorimeter. You cannot get consistent or reliable results and will waste a lot of time. Get your fuels tested by a laboratory. A properly built bomb calorimeter will give results in duplicate in less than 30 minutes. The calorific value of ethanol will be tabulated in the CRC Handbook of Chemistry and Physics. If you have an accurate analysis of these fuels you can calculate the calorific values by weighted average from tabulated values. However not all values are likely to have been measured before. A bomb calorimeter burning an oil will require 0.25 to 0.5 grams of sample, for a high ethanol mix you might need 0.6 to 0.8 grams of sample as the C.V. of ethanol is not very great. Any more than that will probably overheat the bomb and water and a measurement will be impossible.

Analyse exhaust gases by gas chromatograph, preferably using one set up as a refinery gas analyser, mine air analyser or transformer gas analyser. Last one I used cost the laboratory over $40,000. However these cannot analyse for S02 or H2S since these gases are so reactive that they are absorbed by the sampling equipment or the innards of the chromatograph itself. You might be able to take samples in large Mylar bags and have them tested at a smog testing place. The chromatograph will give results for H2, CO2, C2H4, C2H6, O2, N2, CH4 and CO and perhaps a few other gases. Other methods will include non-dispersive infra-red photometers for CO2, and total hydrocarbons and a paramagnetic analyser for O2. You will also want to measure the water content.

The best inexpensive way to analyse for sulphur is in the input fuel, this could be a gravimetric analysis using Eschka's Mixture or a titrimetic analysis with a high temperature tube furnace. However the sulphur content of most plant oils is very low, though I don't know about Jatophra oil. These are standard tests in coal laboratories, as are calorific value tests. The cost per test is fairly low, since the lab will do many of these every week. A coal laboratory can also analyse for total carbon, hydrogen and if you want, nitrogen, phosphorus, arsenic etc in the fuels.

Experience with various forms of Diesel engines running biodiesel and straight vegetable oil shows insignificant changes in power output at the rear wheels over running petro-diesel. Some vehicles produce a few more hp, like 3 to 5, some a little less, like 3 to 5. You will not be able to fuel a common-rail Diesel engine (the most recent type) on unmodified straight vegetable oil. In general, Diesel engines with indirect injection can burn straight unmodified vegetable oil for thousands of hours without damage, apart from some build up of carbon on the injectors which is relatively easily fixed. However injector pumps usually cannot handle the strain of the viscous vegetable oil and it is best to heat the fuel to perhaps 140F first to reduce the viscosity. Even this is not enough for some injector pumps which will fail quickly. The only vehicles that seem to combine an adequate injector pump and indirest injection are 20-year-old Mercedes Benz cars using the 5- and 6 cyclinder engines introduced in the late 1970s or early 1980s. Even then people converting them to vegetable oil, set up heating systems for the vegetable oil.

Engines using direct injection will last several hundred to a few thousand hours on straight vegetable oils but then will go into severe engine damage from accumulation of carbon around the piston rings and the injectors. To fuel such engines, trans-esterified biodiesel is needed. I do not know whether biodiesel will run in common-rail engines.