1. Rajshahi University of Engineering & Technology Bangladesh.
2. Rajshahi University of Engineering & Technology Bangladesh.

*             Correspondence: faisal.bdmail@gmail.com

Keywords: biodiesel, pitraj oil, diesel engine

1. INTRODUCTION

Now a day the world is highly dependent on petroleum fuels for generating power, vehicle movement, agriculture and domestic useable machinery operation and for running the different industries. Every year about 137000 vehicles comes from manufacturing region [1]. Most of the vehicle based on petroleum fuel. So With technological progress and improvement of living standard of the people the demand of the petroleum fuel increases simultaneously. But the reserve of the petroleum fuel is limited & is evenly distributed in such a way so that many regions have to depend on the others for their fuel requirements [2]. The price of the petroleum fuel is also increasing day by day and use of the petroleum fuel in engine produces harmful products which pollutes the environment. Due to the above reason, attention has gone to the search of renewable source of fuel which can meet the demand locally [3]. Vegetable oils may be an alternative renewable source of diesel fuel known as “biodiesel” which can be produced in any local area. Vegetable oils and their derivatives (especially methyl esters), commonly referred to as “biodiesel,” The use of vegetable oils in diesel engines is nearly as old as the diesel engine itself [4]. They are technically competitive with or offer technical advantages compared to conventional diesel fuel. Many researchers have shown that using raw vegetable oils for diesel engines can cause numerous problems. Vegetable oils have increased viscosity, low molality, cold flow properties and certain number causes injector cocking, piston ring sticking, and fuel pumping problem and deposit on engine [5]. These problems limit the direct use of vegetable oil in engine in place of conventional diesel. However the above limitation can be greatly minimized by converting the vegetable oil into ester through esterification which is named as biodiesel [6]. But due to limited availability of agricultural land the factor edibility of vegetable oil and its higher prices greatly restricts the scope of using esterified vegetable oil as fuel [7]. There is a chance to overcome this restriction if waste and non-edible vegetable oil is used as feed stock for bio-diesel plant. The products of diesel produce a lot of hazardous emission like carbon-di-oxide (CO2), carbon mono oxide (CO) sulfur-di-oxide (SO2) nitrogen- di-oxide (NO2), particulate matter (PM10), unburned hydrocarbon (UBHC), 1,3 butadiene, visible smoke(CH2CHCHCH2),noise and odor [8]. Studies accused diesel combustion as the main reason of “Global Warning”, on the contrary, bio-diesel is biodegradable, and they do not contain any sulfur [9]. As a result the products of combustion of the bio-diesel do not produce sulfur-di-oxide   (SO2). The main advantage of using bio diesel in diesel engines is neutral carbon-di-oxide (CO2) emissions. This is possible by following way. When bio-diesel will be used in engine in regular and large basis, more plants have to plantation to mitigate the oil demand [10]. On the other hand that plant will use the carbon-di-oxides emitted from the engines for their food production. As a result there will be established a food chain between the engine and bio-diesel resources in an indirect way and such a process satisfy the neutral condition of carbon-di-oxide (CO2) emissions [11]. For the variation of climate, soil condition etc. different countries search the different vegetable oils to replace the diesel fuel. Malaysia is searching the feasibility of palm oil for diesel fuel substitute; in Russia and Australia experiment has been carried on the rapeseed oil Bangladesh is an under developing country [12]. It’s energy demand increasing day by day. The annual demand of diesel fuel in our country is about 37 million liters [13]. For this demand country totally dependent on foreign countries and large amount of foreign currencies are spent to import the diesel fuel. If esterified vegetable oil is used to some extent in place of diesel fuel, a vast amount of foreign currencies will be saved. But in Bangladesh is highly populated country, there are about 15 cores people live in this country and cultivable land is very limited [14]. The total amount of edible oil produces in our country cannot meet the domestic demand, substantial amount of edible vegetable oil is imported every year to meet the demand and the price of vegetable oil is greater than that diesel fuel. So there is no chance of to use to use the edible vegetable oil as feed stock for biodiesel [15]. In aspect of Bangladesh non-edible renewable pit raj (local name) oil (aphanamixis polystachya) can play a vital role in the production of substitute diesel fuel [16]. The climatic and soil condition of Bangladesh is also suitable for the production of this plant. Our attention goes to the pit raj oil because it is non- edible renewable source of oil & it is a new research over the world. The climate of our country is good to cultivate [17]. The oil as well as biodiesel can be prepared with most economical way. By increasing pit raj plantation in our country, we can meet our domestic demand and save our capital. Finally the byproduct of Trans esterification can be used in the soap industry .This also save our capital and reduce cost [18]. At present 100 percent bio-diesel is not used in place of diesel fuel to run the engine, because 100 percent bio-diesel causes significant reduction of brake thermal efficiency, higher specific fuel consumption& excessive Nox formation. This problem can be greatly minimized by using diesel biodiesel blend & additives for Knox formation. The most widely used blends are B10 (10 % bio, 90 % diesel) & B20 (20 % bio, 80 % diesel). Diesel biodiesel doesn’t cause significant increase of NOx & reduction of brake thermal efficiency. Meanwhile the other performance parameter of the engine is like as net diesel fuel.

3. MATERIALS AND METHODS

Biodiesel is a diesel fuel substitute produced from renewable sources such as vegetable oils, animal fats, and recycled cooking oils. Chemically, it is defined as the mono alkyl esters of long chain fatty acids derived from renewable lipid sources. Biodiesel is typically produced through the reaction of a vegetable oil or animal fat with methanol or ethanol in the presence of a catalyst to yield glycerin and biodiesel (chemically called methyl or ethyl esters). Biodiesel was made by transesterification method. It is the most common method to produce biodiesel from vegetable oil. The transesterification process reduces the density, viscosity, long chain of carbon & increases the cold flow properties of the oil. Transesterification is the process of using an alcohol (e.g. methanol, ethanol or butanol), in the presence of a catalyst, such as sodium hydroxide or potassium hydroxide, to break the molecule of the raw renewable oil chemically into methyl or ethyl esters of the renewable oil, with glycerol as a by-product. Transesterification of vegetable oil.

Figure 01: Transesterification of fatty acid and typical chain structure of fatty acid methyl ester.

The engine used in this experiment was a single cylinder water-cooled, naturally aspirated (NA), 4-stroke, DI (pitter) diesel engine. The specifications of the engine are shown in table. The experiment was conducted with conventional diesel fuel, pitraj oil methyl ester. The RPM was measured directly from the tachometer attached with the brake dynamometer. The fuel injection timing was set at 24BTDC (before top dead center). The exhaust gases including NOx, CO, were measured with a portable digital gas analyzer (IMR 1400). The data of exhaust emissions were taken from the end of the exhaust pipe of the engine. Engine noise is measured by using sound meter setting 2 feet distance from the engine. The engine speed was selected by varying the speed under maximum efficiency keeping load constant The exhaust gas temperature was measured by the gas analyzer from the exhaust pipe under the constant speed was selected & varying the load. Fuel consumption was measured by a burret attached to the engine fuel. A stopwatch was used to measure fuel consumption time for every 10 cc fuel. The engine was electrically loaded. The engine was first run at load 35.59 N by varying rpm from 600 to 1250 rpm and maximum efficiency is obtained at 700 rpm. Now the engine is operated about 30 minute with diesel fuel so that the engine became sufficiently warm up. The engine was run at the fixed rpm (700) and loads were varied from 3 lb to 15 lb. Each time corresponding data of exhaust gas temperature, emission, fuel consumption were measured and noted for the diesel & diesel biodiesel blend. The volumetric blending ratio of biodiesel to diesel fuel was set at 10%, 15%. A gas analyzer was used to measure the exhaust gas emission. Every test was carried up to three times for getting maximum reliable results.

Table 01: Engine specifications

Engine type	4-stroke DI diesel engine (AVI)
Number of cylinders	One
Bore x Stroke	80 x 110 mm
Swept volume	553 cc
Compression ratio	16.5:1
Rated power	4.476KW@1800 rpm
Fuel injection timing	240 BTDC

Table 02: Gas Analyzer specifications

Items	Description
Power supply	230V / 50-60 Hz.
Charging time	Fill charge 625h. Operating time 8h state of charge is displayed
Fuels	Light oil, natural gas, town gas, coal gas, liquid gas.
Printer	Thermo printer, 58 mm wide paper roll.
Gas probe	Heated probe with PTC resistor temperature 650C cone. Thermocouple NiCrNi.
Gas hose	3 way hose, length 3.5m.
Memory	Buffered.
Sensor	3 portable sensor; CO, NOX, O2.
Air probe	Integrated current sensor.
Condensate trap	Bulb type manually emptied.
Dust filter	Cellpor-filter, 4 micron.
Dimension	430 X 290 X 190 mm.
Weight	7.5 kg.
Operating Temperature	-100C bic to 400C.
Storage temperature	-200C bic to 500C.

Table 03: Properties of diesel, biodiesel & pitraj oil.

No.	Properties	Neat diesel	Pitraj oil	Neat Biodiesel
1	Density (gm/cc)	0.86	0.948	0.87
2	Viscosity (c.st) @ 23ºC	4.98	8.04	6.22
3	Higher heating value (kJ/kg)	44579	*	38588
4	Cetane index	47	*	51
5	Flash point (ºC)	74	*	153
6	Fire point (ºC)	84	*	164
7	Copper corrosion	negligible	*	No

4. RESULT & DISCUSSION

4.1 Growth Parameters

While neat vegetable oils are competitive with conventional diesel fuel in some emission categories, problems were identified for other kinds of emissions. For example, it was shown that PAH emissions were lower for neat vegetable oils, especially very little amounts of alkylated PAHs, which are common in the emissions of conventional diesel fuel. Besides higher NOx levels, aldehydes are reported to present problems with neat vegetable oils. Total aldehydes increased dramatically with vegetable oils. Formaldehyde formation was also consistently higher than with diesel fuel. It was reported that component TGs in vegetable oils can lead to formation of aromatics via acrolein (CH2=CH-CHO) from the glycerol moiety. Another author observed significantly lower emissions of C3 aldehydes (for example, acrolein) for methyl esters of Neemseed oil than for the oil itself. Another study attributes increased emissions of aldehydes and ketones when using vegetable oils as fuels to the formation of acidic water during decomposition of the oils. This acidic water could be an indication for the formation of short-chain oxygenates which likely ignite poorly compared to the long-chain carbon-rich fatty compounds.

Figure 02: Variation of higher heating value for different biodiesel blends.

From fig-10 it is seen that heating value of the biodiesel is lower than that of conventional diesel. This is due to the fact that biodiesel contains about (10-12) % oxygen. Oxygen doesn’t liberate heat during combustion because oxygen cannot burn itself. It only helpful to burn the other elements (carbon & hydrogen) on the other hand conventional diesel doesn’t contain oxygen. Figure shows higher heating value diesel, biodiesel blend decreasing with the increase in percentage of biodiesel in the blend. With the increase in biodiesel percentage in blends the amount of oxygen per gram of fuel also increases. This increase percentage of oxygen reduces the higher heating value of the blends.

Figure 03: Effect of engine speed on brake thermal efficiency. (Load 35.59 N)

Result has been illustrated the variation of brake thermal efficiency with engine speed. From the figure it is seen that the brake thermal efficiency of engine increases with increase of engine speed at constant load (35.59 N). After reaching maximum value the efficiency decreases. This is due to the fact that, initially with the increase of engine speed the torque produced by the engine increases, hence the efficiency also increases. But at higher rpm (> 700) more amount of fuel is injected into the engine cylinder per cycle & due to higher engine speed these fuel doesn’t get sufficient time to burn completely which reduce the efficiency of the engine. Hence the maximum efficiency obtained at 700 rpm.

Figure 04: Effect of BMEP (brake mean effective pressure) on brake thermal efficiency (Engine speed 700 rpm).

It illustrates the variation of brake thermal efficiency with engine BMEP (brake mean effective pressure) with diesel & biodiesel blends. It presents that the efficiency of engine increases with the increase in engine BMEP and decreases after reaching maximum value Because from the equation of brake thermal efficiency with increase in engine BMEP the engine torque increases as well as increase the thermal efficiency of the engine. At higher load more amount of fuel is injected into the engine cylinder which cannot burn completely. It causes higher bsfc (brake specific fuel consumption) and low brake thermal efficiency. The figure also shows that efficiency of biodiesel blends is lower than that of neat diesel. This drop in efficiency is due to the poor volatility, higher viscosity & higher density of biodiesel.

Figure 05: BSFC (Brake specific fuel consumption) Vs engine speed for diesel & biodiesel blend. (Load 35.59 N)

From figure it is seen that the brake specific fuel consumption (bsfc) for biodiesel is higher than the diesel fuel under given condition. At the lower speed the consumption is higher & decreases to a minimum value then increases. The fuel consumption increases with increasing engine speed but at low speed the torque develops as well as power is low. So the brake specific fuel consumption (bsfc) is high at low speed. The torque increases with increasing engine speed & maximum at certain speed cause minimum bsfc. Further increase the engine speed the torque decreases & the bsfc increases. The brake specific fuel consumption for biodiesel blend is higher than the diesel due to lower power than diesel.

Figure 06: Engine torque Vs speed curve for diesel & biodiesel blend. (Load 35.59 N)

Figure illustrates the variation of torque with engine speed at constant load. At low speed the torque is low & increases with increasing engine speed. Further increase the engine speed causes the torque decreases due to reduction of time to burn the fuel completely. Hence incomplete combustion reduces the pressure inside the engine cylinder & also reduces the torque at the engine crankshaft. The torque for biodiesel blend is always lower than the diesel fuel. Because biodiesel contain excess oxygen that only help to burn the fuel but not burn itself. Besides the heating value for biodiesel is lower than the diesel fuel. Lower heating value produce smaller energy inside the engine cylinder.

Figure 07: Engine power Vs speed curve for diesel & biodiesel blend. (Load 35.59 N)

From figure it is seen that the engine power at low speed is smaller & increases with increasing the speed. The power is maximum at certain engine speed. Further increase the engine speed the power decreases. Because at higher engine speed although the fuel consumption is higher but the torque develop is lower due to small time to burn all the fuel. The power mainly depends on the torque characteristics which described. The power for biodiesel blend is always lower than diesel fuel under given condition. Because biodiesel contain excess oxygen & lower heating value which reduce torque as well as power.

Figure 08: Variation of engine noise with % of biodiesel. (Engine speed 700 rpm, load 20.44 N).

Figure illustrates the variation of engine noise with % of bio diesel, the engine noise comes from the mechanical linkage in the engine cylinder & thrust of combustion product. From the figure it is seen that the noise level for the biodiesel blend lower than that the neat diesel for the same condition with increasing the % of biodiesel. This characteristics prove that the biodiesel contain better lubricity property than that the neat diesel which reduce the engine noise. The reduction of engine noise increases the engine life & improves the sound pollution in the environment.

Figure 09: Variation of CO emission with engine BMEP for neat diesel & bio diesel blends. (Engine speed 700 rpm)

Result shows the effect of engine load on CO emission, in diesel engine combustion takes place normally at higher A/F ratio, therefore sufficient oxygen is available to burn all the carbon in the fuel fully to C02. This oxidation reaction is not irreversible reaction like oxidation of nitrogen and the process is limited (below certain temperature level, < 1500K) by the phenomenon of dissociation. During this dissociation CO2 splits into CO and O2. If sufficient energy is supplied to CO2, collision takes place between some of the CO2 molecules. For biodiesel CO emission level is lower than that of diesel fuel, because bio- diesel supplies extra 10% to 15% oxygen. Due to the presence of extra oxygen, additional oxidation reaction takes place between oxygen and CO. This oxidation reaction lowers the CO emission by producing extra CO2 by complete combustion.

Figure 10: Variation of NOx emission with engine BMEP for neat diesel & biodiesel blends (Engine speed 700 rpm)

Figure illustrates the effect of engine load on NOx emission. Naturally NOx emission increases with the increase in engine BMEP. It is well known that nitrogen is an inert gas, but it remains inert up to a certain level (1100 0C) and above this level it does not remain inert and participate in chemical reaction. At the end of combustion, cylinder gas temperature arises about 2500 0C. At this temperature level oxidation of nitrogen takes places in presence of oxygen inside the cylinder. On the other hand, since the formation of nitrogen oxides do not attain chemical equilibrium reaction; then after the end of expansion stroke when the burned gases cool and the formation of NOx freeze, the concentration of the formed NOx in the exhaust gas remain unchanged. This figure also shows that NOx level is higher for biodiesel blend than conventional diesel fuel at same engine load. Biodiesel contains about 10% to 15% more oxygen than normal diesel fuel. This additional oxygen is responsible for extra NOx emission.

4.1 Growth parameters

Studies report that, at least in short-term trials, neat oils gave satisfactory engine performance and power output, often equal to or even slightly better than conventional diesel fuel [19]. However, vegetable oils cause engine problems, this was recognized in the early stages of renewed interest in vegetable oil-based alternative diesel fuels. Studies on sunflower oil as fuel noted coking of injector nozzles, sticking piston rings, crankcase oil dilution, lubricating oil contamination, and other problems [20]. These problems were confirmed and studied by other authors. A test for external detection of coking tendencies of vegetable oils was reported [21]. The causes of these problems were attributed to the polymerization of TGs via their double bonds which leads to formation of engine deposits as well as the low volatility and high viscosity with resulting poor atomization patterns. An oxidative free-radical mechanism was suggested as governing TG polymerization in lubricating oil contamination when using sunflower oil as fuel [22]. Fumigation with propane was studied as a means to reduce injector coking. The engine problems have caused neat vegetable oils to be largely abandoned as alternative DF. Generally, most emissions observed for conventional diesel fuel are reduced when using esters. NOx emissions are the exception [23]. In an early paper reporting emissions with methyl and ethyl ester as fuel, it was found that CO and hydrocarbons were reduced but NOx were produced consistently at a higher level than with the conventional reference diesel fuel. Similar results were obtained from a study on the emissions of rapeseed oil methyl ester. NOx emissions were slightly increased, while hydrocarbon, CO, particulate and PAH emissions were in ranges similar to the diesel fuel reference [24]. As mentioned above, the esters emitted less aldehyde than the corresponding neat rapeseed oil. Unrefined rapeseed methyl ester emitted slightly more aldehydes than the refined ester, while the opposite case held for PAH emissions [25]. A 31% increase in aldehyde and ketone emissions was reported when using rapeseed methyl ester as fuel, mainly due to increased acrolein and formaldehyde, while hydrocarbons and PAHs were significantly reduced, NOx increased slightly, and CO was nearly unchanged [26]. The study on PAH emissions, where also the influence of various engine parameters was explored, found that the PAH emissions of sunflower ethyl ester were situated between diesel fuel and the corresponding neat vegetable oil [27]. Reduced PAH emissions may correlate with the reduced carcinogenity of particulates when using rapeseed methyl ester as fuel [28]. The general trend on reduced emissions except NOx was confirmed by later studies, although some studies report little changes in NOx. In a DI engine, sunflower methyl ester produced equal hydrocarbon emissions but less smoke than 75:25 blend of sunflower oil with diesel fuel. Using a dieseloxidation catalyst in conjunction with soy methyl ester was reported to be a possible emissions reduction technology for underground mines [29].

5. CONCLUSION

Growth parameters viz., plant height, number of leaves per plant was studied at 25, 50, 75 and 100 days after transplanting and at harvesting stage. Different sources of nitrogen showed remarkable effect on plant height, number of leaves, dry matter percentage of bulb at all the stages. The highest plant height, number of leaves per plant and dry matter percentage were recorded in variety N-53 followed by Red Creole, Agri Found Dark Red. Variety Agri Found Light Red had lowest values for all these growth attributes. Result recorded highly significant effect on bolting percentage. The investigation revealed that there was significant effect of varieties on neck diameter, polar and bulb diameter, average weight and total yield of onion bulb. Different sources of nitrogen revealed significant influence on growth attributes at all the stages. The highest plant height, number of leaves per plant and dry matter percentage of bulb were found at (50% N by Urea + 50% N by PM) followed by (Full dose of N by PM) and the lowest growth attributes were recorded under (Full dose of N by Urea). Different sources of nitrogen had significant influence on neck diameter, polar and bulb diameter of onion bulb, average weight of bulb, total bulb yield and T.S.S. content in bulb and biological yield, harvest index, single center and marketable bulb yield. The result recorded highly significant effect on bolting percentage of variety. Interaction effect of varieties and different sources of nitrogen was non-significant on dry matter percentage of onion bulb. Plant height and number of leaves per plant showed non-significant influence of interaction effect of varieties and different sources of nitrogen. Interaction effect of varieties and different sources of nitrogen did not show any significant effect on neck thickness of bulb, polar as well as bulb diameter, bolting percentage and T.S.S. content of onion bulb. Hence, among the evaluated varieties of onion (Allium cepa. L) N-53variety was found best for response of different sources of nitrogen and the varietal response was more effective to (50% N by Urea + 50% N by PM) than other treatments.

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