Results

     A higher viscosity of a fuel can lead to problems related to incomplete combustion or excessive smoke emissions.  Although the biodiesel had properties of higher viscosity compared to the No. 2 diesel fuel, no evidence of combustion problems were found.  When fuels are burned, carbon deposits form, known as Conradson carbon residue (CCR).  A strong correlation exists between the carbon content of a fuel and deposit formation at the injector, suggesting problems will occur with combustion of waste olive oil methyl ester.  However, the researchers observed no problems related to incomplete combustion or abnormal carbon residue.

     Knothe and Dunn, from a different journal on using vegetable oil as a candidate for biofuel, states that saturated hydrocarbon chains, found in fatty acids, are especially suitable for conventional diesel fuel.  Fatty acid composition are not considerably different between used and unused oil.  Used olive oil represent up to 15% of the saturated chains, whereas saturated chains of canola oil are in the range of 5%-7%.  Soybean oil are in the range of 4.7%-17%, and those from sunflower oil are in the range of 4.8%-12.1%.  The laboratory measures support the idea that olive oil methyl ester provides a more suitable value to be considered as a biodiesel-fuel alternative.

     The cold filter pluggins point (CFPP) relates to operating conditions during cold weather.  Table 1 shows olive oil methyl ester to have a CFPP of -9 ^oC, a better value than vegetable oil, which is -5 ^oC.  The major problem associated with the use of biodiesel is its poor low-temperature flow properties, documented by having a high cloud point (CP) and pour point (PP).  CP is the temperature at which crystals form and solidification of saturates occur.  PP is the lowest temperature at which fluid will still flow.  Major operating problems will result from clogged fuel lines and filters due to temperature decreases as more material solidifies.  Engine manufacturers recommend a CP below the temperature of use and not more than 6 ^oC above the PP.  The CP of used olive oil methyl ester is -2 ^o C - the same for rapeseed oil methyl ester and lower than temperature of soybean oil methyl Ester and sunflower methyl ester.  Engine starting on waste olive oil methyl ester nearly proved effortless, indicating suitability of the CP and PP values.  Difficulties have been observed with engine starting when using biodiesel from sunflower oil and curcas oil, respectively.

     The parameter for No. 2 Diesel for determining combustion quality is known as the cetane number (CN).  More accurately, the cetane number is a measure of the fuel's ignition delay, from the start of injection to the start of combustion of the fuel.  Cetane is an unbranched open chain alkane molecule that ignites very easily under compression, given a CN of 100, while alpha-methyl napthalene was assigned a cetane number of 0.  All other hydrocarbons in diesel fuel are indexed to cetane.

     CN is not applicable to biodiesel.  Instead, an alternate parameter to determine combustion quality is the cetane index (CI).  Table 1 (from Part 1) shows an appropriate value in comparison to the CN for No. 2 diesel fuel.  Used olive oil methyl ester presents a value of 39.67 MJ/kg, similar to biodiesel from rapeseed oil, soybean oil and sunflower oil, but smaller than No. 2 diesel fuel (47 MJ/kg).

     Engine power results are similar between No. 2 diesel fuel and the olive oil methyl ester biodiesel.  The maximum engine power slightly increased by 5.7% using biodiesel instead of No. 2 diesel fuel during engine startup, but a minor loss in maximum power occurred by 2% when biodiesel was used instead of No. 2 diesel fuel; given the accuracy of the engine dynamometer, engine behavior seems to be normal.  Mittelbach and Tritthart found similar results using biodiesel from waste oils, and several researchers observed engine-power losses up to 10% using biodiesel from straight vegetable oil.

     Different loads and speed settings generated various performance curves.  The following equation integrates the N-w surface at maximum load considering an engine speed within 1300-2300 rpm to calculate engine power output.

The presented equation (1) helps clarify the percentage differences between each test, compared to No. 2 diesel fuel.  N_i is the engine power in kilowatts.  S₀ corresponds to that of diesel fuel at the beginning of the test, and S_i is the power-speed area value for each test.

Table 2 reveals results of slight differences between biodiesel tests and the No. 2 diesel-fuel test at 0 h, consistent with the lower biodiesel energy delivery.  A power loss of 7% occured with No. 2 diesel fuel, running the engine at 0 h to 50 h.

     Brake-Specific Fuel Consumption (BSFC) is a measure of fuel efficiency with a shaft reciprocating engine.  Brake-specific fuel consumption volume (V) was calculated by equation 2:

Units of g (kW h)^-1 describes the brake-specific fuel consumption, q_jk.  Values were chosen to simulate the usual requirements of the engine.  Brake-specific fuel consumption in biodiesel increased by approximately 6.4% compared to No. 2 diesel fuel.  However, brake-specific fuel consumption in biodiesel increased by 26% after the engine was running for 50 h.  Several authors found similar results using biodiesel from straight vegetable oil.  Graphic results are shown in Figure 1.

Panel b1 shows data for diesel fuel at 0 h, whereas panel b2 shows data for waste olive oil methyl ester after 50 h.  Variation of specific fuel consumption between each test and the No. 2 diesel fuel was not significant, and statistical analysis showed experimental error irrelevant in findings.

Energy Delivery/Energy Consumption:

A relationship between energy output and energy input determines whether the use of the biodiesel affects engine performance.  A higher viscosity of the biodiesel requires all report of energy loss in the injection pump or in the combustion chamber.  Equations 3 and 4 calculates energy output and input.  Equation 5 represents the quotient (R) between both values, considering only engine speeds of 1300-2300 rpm only.

E_DELIVERY is the energy delivered per cycle by the engine (Joules/cycle).  E_CONSUMPTION is the energy provided per cycle by the fuel (Joules/cycle).  Table 2 shows a slight increase by 6% using waste olive oil methyl ester during the engine start tests, but no differences were occurred after the engine had been running for 50 h when comparing both No. 2 diesel fuel and waste olive oil methyl ester tests.  Panel c1 on Figure 1 shows data for No. 2 diesel fuel at 0h, whereas panel c2 shows data for biodiesel after 50 h.

Discussion/Conclusion (based on the journal)

The results are encouraging.  Energy conversion efficiency is almost the same for both fuels, and even a slight increase is noticeable.  Carbon deposits and wear levels seemed normal, and no known difficulties of engine starting existed.  The engine performance on the biodiesel was satisfactory throughout the entire test, and smoke emissions from use of the biodiesel were lower than that of No. 2 diesel fuel.  Waste olive oil methyl ester can be recommended as a diesel fuel substitute, if long-term diesel-engine tests provide satisfactory results.

Acknowledgements

Work done by M. P. Dorado, E. Ballesteros, J. M. Arnal, J. Gomez, F. J. Lopez Gimenez, and all their supporters and references.

Wikipedia (used to obtain definitions only; not considered a citeable source)