fact they have technical means to produce electricity, diesel fuel must be provided. To fill the generators sets, the fuelhas to be transported from large vendors to those communities, roughly increasing the price two to three fold. The availability of biomass in most part of the country, especially in the Rain Forest, may turn gasification of therenewable resources an important option in bringing cheaper and reliable electricity to those communities. Thesynthesis gas could be premixed with air and burnt in a compression ignition engine. Biomass gasification in small units is a proven technology. Typical drawbacks of the entire process, like tarseparation, cooling and filtration of the synthesis gas are now dealt with some degree of success, and by more frequentintervention to the engine and the gasification system. Technical requirements for such units are far less restrictive thanthose claimed by larger systems. Dasappa et al. (2004) reported the existence of over 30 gasification units operating inIndia and abroad accumulating more than 80,000 hours of experience. The gasifiers are of downdraft type with all theauxiliary system for gas clean-up, ash handling, water treatment, and so on. They claimed the system to be reliable forvillage electrification. The mechanical power, from standard engines, was obtained either from dual fuelling (diesel andgas) or gas alone operation. The authors claimed that for small biomass gasification plants, a downdraft reactor wouldgive more chance of success in designing the system for low tar content. In dual fuelling operation, many gaseous fuels burn simultaneously with diesel, such as hydrogen (Gopal, et al.,1982), biomass-charcoal synthesis gas (Batthacharya et al., 2001), biogas ( Henham and Makkar, 1998), ethanol(Noguchi and Sakata, 1996), to mention a few. More recently Singh at al. (2006) tested the performance of dieselengine in dual mode operation with a blend of refined rice bran oil (RRBO) and fossil diesel (FD) along with producergas from a wood gasifier. Stable operation was reported up to the point in which the blend contained 25% of diesel fueland 75% vegetable oil (RRBO). Performance and emissions characteristics of diesel engines fueled by vegetable oils were also investigated byYoshimoto et al. (2001). The engines tested had two combustion chamber configurations, bowl in piston and toroidal.The base fuel, in part of the experiments, was rape-seed oil blended with several kinds of alcohol. One importantconclusion drawn from the work was that, the addition of alcohol to the vegetable oil realized good stable combustion. Based on these renewable resources (biomass and vegetable oil) we present, in this work, experimental results of anew technological concept for rural electrification based on diesel engines and biomass gasification. We were able tocarry out stable operation of a diesel generator set with straight (pure) vegetable oil burning simultaneously withsynthesis gas produced by gasification of endocarps. In a sense, this paper can be thought as one extension of the workof Singh et al. (2006), by firstly considering we were able to use 100% pure vegetable oil as the pilot flame (dual fueloperation), and secondly because the feedstock of the gasifier was the endocarp of the plant from which the oil itselfwas extracted. Two combinations of bio-fuels were tested in a 12.5 kW unit, Orbignya sp. (babaçu) and Acrocomiaaculeata (macaúba). In both cases straight vegetable oil (SVO−1 and SVO−2) was injected into the engine while therespective endocarp of the plant was gasified in a stratified downdraft reactor producing what here is referred assynthesis gas (SG−1 and SG−2). Index 1 for SVO and SG refers to Orbignya sp. and 2 for Acrocomia acuelata.2. RENEWABLE FUELS As a tropical country, Brazil has plenty of renewable sources suitable for producing electricity. Distributedgeneration may be provided by photovoltaic cells, small hydropower plants, direct burning of biomass in steam cycles,burning of pure vegetable oil and biodiesel in small diesel engines as well as through biomass gasification and furtherburning of the synthesis gas. In another paper, it is discussed the productive chain of Orbignya sp. (babaçu) andAcrocomia aculeata (macaúba) for small scale power generation (Xavier et al., 2009). Out of uncountable possibilities,the paper addresses these two species as an instance of what could be a technical proposition towards a sustainableelectrification of remote communities, and mostly to help establish foundations towards local economic development. The extraction and further processing of plant oils require energy. Human effort and animal power have beentraditionally employed on those communities to execute many of the daily tasks while pursuing some sort of incoming.Manpower has also to be invested in subsistence activities like in crops growing, oil and food gathering (fruits andnuts), hunting, fishing and so on. An intermediate stage of economic development would be reached if electrificationtakes place followed by some sort of mechanization. As an example, some medicinal and cosmetic oils are pre-processed and sold as a raw material for large enterprises. Mechanization of the process would free residents to beinvolved in other activities while still generating incoming. More importantly, knowing that the oil is only a smallportion of the extracted biomass one should seek means to bring value for the byproducts of the productive chain. Forinstance, the endocarp of the plants contains, in most cases, the largest portion of the biomass and could easily beexploited as a feedstock for a gasification reactor. Table 1 shows the share of the biomass and oil from the fruits underinvestigation. It can be seen that the endocarp is the second largest (29%) component in the fruit for macaúba, and thelargest (58%) for babaçu. Both feedstocks are excellent candidates for biomass gasification, on account of their highcharcoal yield after carbonization in temperature above 300° C (Silva and Brito, 1986). The authors reported carbonyields of the order of 38 and 44%, respectively after carbonization of the endocarp of babaçu, which are higher thanthat give after carbonization of eucalyptus wood, under the same conditions. Depending on the amount of oil extracted,
were installed, controlled by solenoid valves to set which fuel should be injected for that experiment. The pre-heating ofthe vegetable oil, as needed for viscosity correction, was obtained by electric trace heaters, 80 W each, positioned alongthe fuel line between the diesel pump and the fuel injectors. The capacity of the trace heaters allowed the vegetable oilto be heated from just over 65° up to about 120° C, depending on power demand. Lower injection temperatures wereassociated with higher power demands, because of larger fuel flow rates for a constant heat supply. This heating systemallowed the unit to be started with pure vegetable oil without relying in diesel fuel for cold start. Figure 2. Test apparatus - gasification unit, diesel generator set, resistance bank and instrumentation. The generator set was assembled by Heimer Brazil Ltd; model GEHK-18 (220 V, 60 Hz). The rotational speed was1800 rpm with maximum power delivered of 12.5 kW. Because of constant speed operation, tests were conductedvarying the load, by way of an electric resistance bank with five 2.0 kW and one 1.0 kW water immersion heaters.These heaters were set on and off by electrical switches, depending on the requested load. Supplied energy wasconsumed while evaporating water of the resistance bank. Nominal engine power output was penalized, because testswere conducted at about 1200 m altitude (city of Brasília – Brazil). In our investigation we used a direct injection diesel engine (Kirloskar - India), naturally aspirated, with thefollowing features: • two cylinders; • bore/stroke= (100 mm)/(200 mm); • total displacement = 1884 cm3; • compression ratio = 17; • maximum output = 16.9 kW @ 1800 rpm; The gasification system was comprised of an open top downdraft reactor and a gas cleaning system. The gasifierwas designed to operate in the range of about 300 kg/h/m2 specific gasification rate when coupled to the 1884 cm3(1800 rpm) engine. At this rate, the gasifier most certainly operated outside of the optimum envelope. The reason wasthat the engine maximum power was rated at 16.9 kW, while the generator set was for 12.5 kW. If maximum powerfrom the engine and the generator matched, specific gasification rates would approach an optimum, if considering thefigures presented by Jain and Goss (2000). They performed a large number of tests in a downdraft reactor fed by ricehusk, realizing good performance, for different configurations (diameter of the reactor), at equivalence ratio around 0.4and specific gasification rate of about 192.5 kg/h/m2. Following the reactor, a cyclone was installed for particle capture. Producer gas was cooled by a specially designedheat exchanger, were gas flowed inside the tubes and water outside. While cooling the gas, the superheated steamcondensed retaining most of the tar along the process. This mixture (condensed water and tar) accumulated in a tankpositioned at the lower part of the heat exchanger, for further extraction. After operating the gasifier for a couple ofhours the condensed mixture was sent to a laboratory for composition analysis. Concentration of oils and greasedissolved was estimated as 21 mg/liter, showing very low tar content in gas. Dissolved solids were estimated as 8.5mg/liter, also showing a good particle separation, both by the cyclone and by the steam condensation process. In anycase, the gas was further cooled and cleaned by an organic filter, before the carburetor system. A couple of runs were conducted. Here, we present just the results of two large sets of experiments, the firstgasifying the endocarp of Orbignya sp. (babaçu), injecting the extracted oil, from the nuts of the same plant, into the
SVO−1 (T1, T3 and T5) and SVO−2 (T1, T4 and T6) necessary to sustain a given load. For that, diesel fuel wasreplaced by straight vegetable oil and the wood ships, in the gasifier, by the endocarps from both palm trees. Tests T3and T4 were also carried out as reference cases to derive what levels of oil substitution would be reached in dual-modeoperation, after adding synthesis gas (SG−1 and SG−2) to the intake air. At this point, still no alteration in the fuelinjection system has been made, such as maximum rates and timing. Only when putting into practice tests T5 and T6,the fuel pumping system was adjusted so the maximum rate of fuel injection (straight vegetable oil) should be no higherthan 0.4 g/s. Figure 4 presents the results for SVO−1 as the sole fuel, following test T3 plan, and SVO−1with simultaneousburning of synthesis gas, obtained by gasification of the endocarp of the respective fruit (SG−1) as planned in test T5.Besides the consumption of straight vegetable oil, for both operating modes, the consumption of fossil diesel is alsoshown to help the comparison. The oil temperature range, before injection, was estimated from 91 to 111 °C. Highertemperatures were associated with lower injection rates, because of dual-mode operation. On account of the lower heating value (36305 kJ/kg), the consumption of SVO−1, compared to that of diesel (43559kJ/kg), is everywhere higher for the same power output. The difference seems to be larger as power increases. With theaddition of synthesis gas (SG−1) and reduced fuel injection rate (< 0.40 g/s) it was possible to recover power output toloads lower than 10 kW. In the range of 8 and 9 kW the SVO−1 substitution was of the order of 73%. By simplyallowing the engine to receive synthesis gas, at an assigned load, a decrease in straight vegetable oil injection rate wasrealized. This adjusting took place on account of the added chemical energy, contained in the synthesis gas. Theengine’s governor automatically reduces the amount of oil injected to maintain the rotational speed of the electricgenerator. Higher power outputs could not be obtained because fuel injection was limited to 0.4 g/s. Figure 4: Straight vegetable oil (Orbignya sp.) consumption rate, in sole and dual-mode operation. Figure 5 presents the results for SVO−2 as the sole fuel, following test T4 plan, and SVO−2 with simultaneousburning of synthesis gas, obtained by gasification of the endocarp of the respective fruit (SG−2) as planned in test T6. Acurve showing the consumption of fossil diesel was also included to help comparison. For this oil the injectiontemperature range was 91 to 119 °C. The lower heating value of SVO−1 (37577 kJ/kg) opposed to that of diesel also explains the higher fuelconsumption for the renewable oil for any given power output. In like manner, it was observed here an increase inrelative consumption as power increased. By adding synthesis gas (SG−2) to the intake air, with maximum fuelinjection rate reduced it was possible to recover power output to loads lower than 9 kW. At the maximum load applied,about 9 kW, the straight vegetable (type 2) substitution was of the order of 69%. In a previous investigation, using a different gasifier (downdraft with open top) with larger diameter we could reachbetter figures regarding vegetable oil substitution. With a gasifier with improved specific gasification rate the oilsubstitution was of the order of 80% and the maximum power output was 10.9 kW with fuel pumping system limited to0.40 g/s. The engine derating was less than that with the smaller diameter gasifier. From Fig. 4 and 5 we can see that at almost engine full load (~12 kW) the consumption of vegetable oil was about1.35 g/s. By limiting the injection rate to 0.40 g/s (30% of the reference case) when synthesis gas was burntsimultaneously with vegetable oil, less fuel has to be atomized, thus reducing vegetable oil spray penetration. Becauseof that, the most common engine failure is because of deposits on pistons as well as cylinder walls. Injecting 30% lessfuel would probably extended the time engine breakdown would take place. Premixed flame propagation into the enginewould help in lowering carbon deposits, further extending the time period until engine failure. Considering the villages
10.02 0.07 8.2 9.2 94 0.13 1299 11.77 0.20 9.5 7.4 91 0.31 1378 Table 3. Amount of biomass in different parts of the fruits, for the species considered in this work. SVO‐1+SG‐1 EMISSIONS POWER OUTPUT [kW] CO [%] CO2 [%] 02 [%] HC [ppm] COc [%] NOx [ppm] 1.97 1.02 6.0 13.2 123 2.18 58 3.84 0.97 10.8 7.8 102 1.24 43 5.79 0.56 12.5 6.5 117 0.64 89 8.29 0.39 14.1 4.9 81 0.40 144 9.31 0.47 14.4 4.5 73 0.47 206 Table 4. Amount of biomass in different parts of the fruits, for the species considered in this work. SVO‐2+SG‐2 EMISSIONS POWER OUTPUT [Kw] CO [%] CO2 [%] 02 [%] HC [ppm] COc [%] NOx [ppm] 1.99 1.25 7.9 11.5 139 2.05 48 3.92 1.07 7.9 11.3 104 1.79 104 5.81 0.81 12.0 7.2 95 0.95 69 7.72 0.86 12.9 5.8 75 0.94 138 8.84 1.30 13.8 7.2 63 1.29 15 CONCLUSIONS The main conclusions of this work can be summarized as follows: • Gasification of endocarps of Orbignya sp. (babaçu) and Acrocomia aculeata (macaúba) in a open top downdraft gasifier was accomplished; • Straight vegetable oil obtained from Orbignya sp. (babaçu) and Acrocomia aculeata (macaúba) could be used in a compression ignition engine without penalizing rated power; • It was possible to operate the engine, in a stable manner, in dual-mode operation of SVO and synthesis gas, with reduced fuel injection up to 80% oil substitution; • NOx emissions were greatly reduced while operating the engine with SVO and SG, from both palm species, compared to diesel at any load; • CO emissions were higher for SVO and SG, compared to fossil diesel. The proposed technological arrangement may be an alternative mean to burn, in a long term, straight vegetable oilin compression ignition engines because the injected amount of fuel was less than 30% of that if no syngas is used.ACKNOWLEDGEMENTS The authors would like to acknowledge the support from CNPq, FAPDF and the Ministry of Mines and Energy inthis research.REFERENCESRadu, R. and Mircea, Z., 1997, “The Use of Sunflower Oil in Diesel Engines”, SAE Technical Paper Series 972979.Yoshimoto, Y., Onodera, M. and Tamaki, H., 2001, “Performance and Emissions Characteristics of Diesel Engines Fueled by Vegetable Oils”, SAE Technical Papers Series 2001-01-1807/4227.Babu, A.K. and Devaradjane, 2003, “Vegetable Oils and Their Derivatives as Fuels for CI Engines: An Overview”, SAE Technical Paper Series 2003-01-0767.Lüft, M., Bernhardt, S., Velji, A., and Spicher, U., 2007,”Optimization of Injection of Pure Rape Seed Oil in Modern Diesel Engines with Direct Injection”, DAE Technical Paper 2007-01-2031.