Department of Mechanical Engineering, Sant Longowal Institute of Engineering and Technology, Longowal, PUNJAB: INDIA  -148106

Corresponding author Email: dvijander@gmail.com

Article Publishing History

Introduction

Everybody has a desire to live in comfort and pollution free environment. To achieve comfort, human being introduced machinery in modern world such as engine. Generally engines run on fossil fuel which generates harmful emission and are ultimate cause of pollution and global warming (Ramya et al. 2012). In rapidly growing global energy consumption, diesel engine play the main role (Shameer et al. 2018). Although emission of machinery cannot be eliminated completely but a significant reduction is possible by use of  green fuel or bio fuels. Green fuels have one more advantage that is these are renewable. Bio fuels have been introduced as a substitute for fossil fuels (Yu et al. 2013). (Deshpande and Kulkarni 2012) derived green fuel from Jatropha oil. Animal fats (TAG) and modified vegetable oils in nature can be used for the production of chemical products such as biofuels (Suarez et al .2007). Due to chemical and thermal instability and high viscosity, vegetable oils forms carbon deposits inside the combustion chamber of diesel engines and hence not used directly in engine (Biswas and Sharma 2013). (Buzetzki et al. 2011) used zeolite catalysts with NaY and clinoptilolite to investigate the cracking of vegetable oils (sunflower, rapeseed, jatropha, waste frying oils and soybean). Most of researcher investigated the influence of biodiesel on engine performance, combustion and emissions (Ozener et al. 2014, Zhang et al. 2013, Qi et al. 2010) but very few on green diesel. Biodiesel has few disadvantages like higher viscosity, higher production cost, restriction on feedstock use, low energy density and higher freezing point. (Agarwal 2007, Knothe et al. 2005). Crude palm oil increases the deposit formation in cylinder as compared to petro diesel (Pipitone and Costanza 2018).

The different technologies used a variety of feedstock including lignocelluloses biomass (such as wood and crop residues, dedicated herbaceous or tree energy crops), grains, sugar crops, vegetable oil (soybean, canola/rapeseed, etc.), animal fat (beef tallow, pork lard), and waste cooking greases. These all technologies targeted hydrocarbon products that are similar to petroleum diesel (Milbrandt et al. 2009). (An et al. 2012) computed the combustion and emissions of waste cooking based biodiesel at partial load conditions. (Silitonga et al. 2013) investigated the performance and exhaust emissions of Ceiba pentandra blend biodiesel in diesel engine. Two common techniques are used to produce diesel-type fuel from biomass which are hydro processing and transesterification of triglycerides. Transesterification is used to obtain biodiesel whereas hydro processing is used to synthesize green diesel (Boyás et al. 2012). The cost of feed stock affects the total cost of biofuel significantly. Waste cooking oil (WCO) is more economically viable then vegetable oils, also it is presumed that cooking oil becomes carcinogenic after heating for a long period and it is harmful for health, that is why WCO was selected as a feedstock.

Material and Methods

This experimental work is divided into three parts. The first part of the experiment involves production of green diesel, second part is related to the measurement of key properties of green diesel and third part is associated with performance computation and combustion analysis.

Production of green diesel: For production of green diesel, waste cooking oil was selected as a feedstock where as Na₂CO₃ is used as a catalyst. In the present study green diesel was produced by hydro processing of waste cooking oil. Hydroprocessing completed in two phases (hydrocracking and biocrude distillation). The steps involves in the production of green diesel are shown below in figure 1 with the help of flowchart.

Figure 1: Flow chart of steps involved in the production of Green Diesel

In first step, 1.5 liters waste cooking oil was taken with the help of measuring tube. The quantity of sample has been decided on the basis of capacity of the cylinder of HTHP reactor (2 liters). Na₂Co₃ (anhydrous) was mixed in the sample of waste cooking oil (WCO) as a catalyst. Sample was filled into the reactor, and hydrogen (H₂) was supplied up to 5.5 bar pressure through the inlet vent. Selection of catalyst and optimum pressure of H₂ was predefined on the basis of production optimization. About 87 %(by weight) bio crude could be obtained after hydro processing while the balance 8 % escapes as non-condensable gases and 4-5% water at the bottom of the collecting flask. The resultant bio crude was investigated with respect to appropriate standards and distilled as per ASTM D2892 and ASTM D5236 using the TBP distillation unit, (Rakopoulos et al. 2006).

Different hydrocarbon chain lengths have progressively higher boiling points, so they can be separated by distillation. A fractional distillation tower will heat, vaporize, and then condense into different products. In the present experimental investigation, 1200 ml (1100 gm) bio-crude was taken for distillation. After distillation about 110 ml gasoline, 25 ml aviation/kerosene and 240 ml diesel fraction is being produced. Diesel fuel fraction has been produced at 180-380°C temperature range, aviation fuel between 140-180^oC and gasoline fuel fraction at 35- 140^oC. Different distillates of biocrude oil have different color and different number of carbon. Color of different biocrude oils after biocrude distillation is shown in figure 2. where as carbon atom range shown in Table 1.

Figure 2: Different distillates of bio crude oil

Table 1: Approximate molecular size of crude oil fractions

Fraction                                                                No. of carbons

Gases                                                                     1-4

Gasoline                                                                7-11

Aviation fuel/kerosene                                      9-16

Diesel                                                                    12-22

Residue                                                                >40

Fuel properties of green diesel: Key fuel properties such as specific gravity, kinematic viscosity, cetane number and flash point were measured. (Pham et al.2018) introduced a correlation to predict kinematic viscosity and density of biodiesel. The principle involves the oscillating U-tube which is a technique to determine the density of liquids and gases based on electronic measurement of the frequency of oscillation, from which the density value is calculated. From density, specific gravity of fuel can be calculated. The engine frequency of this container is influenced by the sample’s mass. The direction of oscillation is normal to the level of the two branches. The oscillator’s eigen frequency is only influenced by the part of the sample that is actually involved in the oscillation. These properties were measured as per ASTM D975.Instrument used for measurement of flash point and fire point follows the ASTM D92 – 12b standard. The kinematic viscosity of the oil was determined as per ASTM D 446 –12 using kinematic viscosity bath. The device was manufactured by Lawler Manufacturing Corporation, USA, with Model 86-17D

Performance computation and combustion analysis: Engine test rig was used for basic measurements, which usually should be undertaken to evaluate the performance of an engine on almost all tests, like engine speed, break power, indicated power, fuel consumption. The test engine and dynamometer were controlled by a microprocessor system equipped with data acquisition and logging. Sensors were fitted to the engine and dynamometer to measure relevant parameters and send the data to the control system. The sensors measured engine load, engine speed, inlet air temperature, exhaust gas temperature, lubrication oil temperature, fuel consumption and the cooling water temperature.

Figure 3: Schematic diagram of engine test rig. 1. Test engine 2. Dynamometer 3. Control board 4. Exhaust calorimeter 5. Temperature indicator 6. Cooling tower

Results and Discussion

The fuel properties help us to explain the behavior of fuel. So, it is necessary to measure the fuel properties. The important fuel properties such as specific gravity, kinematic viscosity, net calorific value and flash point etc. were measured in laboratory. These fuel properties for green diesel are shown in the table 2

Table 2: Green diesel fuel properties

Fuel properties                                                         Magnitude

Specfic gravity                                                        0.78

Kinematic viscosity (centi-stoke)                       3.0823

Flash point (°C)                                                      114

Cetane Number                                                      84

Net calorific value (KJ/KgK)                               38823

From the computational data in table 2 it is concluded that green diesel has low specific gravity and high cetane number. Kinematic viscosity about 3.0 centi-stoke which is satisfactory with past research. The net calorific value is 38823 kJ/kg K which has considerable variation with calorific value calculated by Kennedy et al.(2015). The cause of variation may be due to  different feedstock or different production method or may be any device error or due to limited experiment. To overcome this, more experiment need to be performed. The performance parameters: Include indicated thermal efficiency, brake thermal efficiency, specific fuel consumption (kg/kWh), and fuel consumption were calculated at different rpm and at different load condition. Performance data of green diesel observed by this experiment is shown in the table 3 and table 4.

Table 3: Indicated and brake thermal efficiency using green diesel

         Speed (rpm)              Load                           IThEff (%)                BthEff (%)

1490                                0.86                                  83.82                                5.18

1470                                4.90                                  85.76                                21.29

1450                                8.97                                  87.96                                33.97

1430                                12.84                                74.23                                35.98

1410                                16.68                                67.98                                38.14

1390                                20.62                                51.37                                31.20

From table 3 it is observed that if load is increased and engine speed is decreased then initially indicated thermal efficiency and break thermal efficiency both increases but after that they start decreasing. It can be noticed that indicated thermal efficiency is maximum at 1450 rpm and 8.97 kg load whereas maximum break thermal efficiency is 38.14 % at 1410 rpm and 16.68 kg load. BthEff increases with load because if load increases power also increases.

Table 4: SFC & Fuel consumption for green diesel

 Speed (rpm)                  Load (kg)                   SFC(kg/kWh)           Fuel (kg/h)

1490                                0.86                                  1.79                                    0.42

1470                                4.90                                  0.43                                    0.56

1450                                8.97                                  0.27                                    0.69

1430                                12.84                                0.26                                    0.97

1410                                16.68                                0.25                                    1.48

1390                                20.62                                0.30                                    1.67

Specific fuel consumption in kg/kWh decrease with increase in load but it starts increasing when load is increased up to 20.62 kg. This is due to initial increase in brake power with load but after certain value of load, brake power also decreases. The fuel consumed in kg/h increases with load. This is because power requirements increases with load and ultimately consumption of fuel increases

In combustion analysis, the behavior of fuel – air mixture inside the cylinder is analyzed to find out the physics behind the performance and emissions characteristics of the fuel. During  the combustion of green diesel, the variation in pressure, temperature, net heat release, and fraction of fuel mass burned were investigated with crank angle and then compared to petro diesel. Combustion information was obtained from the pressure sensor located in the engine cylinder head. The in-cylinder pressure plot reflects slightly late combustion and larger ignition delay for the green diesel fuels when compared to petro-diesel fuel. In the initial phase of combustion, the pressure rise for green diesel was less because it does not contain smaller length hydrocarbons that can mix quickly with air. Diesel fuel is composed of a wide range of hydrocarbons with varying chain lengths in the range of C-8 to C-21. Green diesel consists of primarily C-11 to C-17 alkenes (Yoon and Lee 2011). The green diesel contains a narrow range (i.e. 11 to 17) which leads to high intensity combustion occurs with. The high pressure values of green diesel fuel  may be a result of better combustion near top dead centre (TDC). Green diesel has the high cylinder pressure peak as compared to petro-diesel. The peak pressure in case of green diesel was 72.8 bar at 376° crank angle and for petro-diesel was 72.2 bar at 376° crank angle. Figure 4 shows the plots of the pressure rise with crank angle for both fuels for complete cycle where as figure 5 show this variation at top dead centre.

Figure 4: In cylinder pressure variation with crank angle

Figure 5: In cylinder pressure variation with crank angle (near the TDC position)

The rate of pressure rise for the green diesel fuels is also noticeably large as compared to petro-diesel fuel. This mainly depends on the fuel’s  chemical and physical properties, which affect the mixing and ignition process. Higher increasing rate of in-cylinder pressure generally leads to more combustion noise.  Figure 6 show the rate of pressure with crank angle.

Figure 6: Rate of pressure rise with crank angle

Figure 7 shows the plots of the net heat release rate for both fuels. The heat release rate curve for both the fuels follow a similar pattern. Both have a pre-mixed combustion phase and a diffusion combustion phase. The green diesel fuels have shorter ignition delays (Dolanimi et al. 2015) and higher heat release rates as compared to petro diesel. The previous literature reported the shorter ignition delays experienced by green diesel fuels and may be due to thermal cracking which tends to break up longer chain hydrocarbons to form smaller hydrocarbons and gaseous compounds which are liable to ignite much faster than their longer chain hydrocarbon counterparts. (Yoon and, Lee 2011). But in present study the combustion results show that the green diesel might not  contain smaller hydrocarbons and gaseous compounds. The combustion results of green diesel are somehow different from the previous publications.  This might be due to  the specific conditions for the current green diesel production process and experimental setup. More experiments are required by altering the production parameters.

Figure 7: Net heat release rate with crank angle

Figure 8 shows the fraction of mass burned with crank angle for both green diesel and petro diesel. From the graph it is observed that at initial stage when the fuel is injected, the fraction of petrol diesel consumed is more than green diesel, at the middle stage it is equal and in later stage fraction consumed of green diesel is more as compared to petro diesel. This is due to high cetane number of green diesel. It will burn at low temperature as compared to petro diesel which have low cetnane number. If a tinny drop of green diesel is injected inside the cylinder it starts burning immediately but when tiny drop of  petro diesel is injected in cylinder it will not burn at this temperature and pressure. Meanwhile another drop injected at same time and piston moves more upward which create more compression. Due to this, temperature will increases which in turn increases the rate of fuel burn.

Figure 8: Fraction of fuel mass burned with crank angle

Figure 9 show variation of gas temperature inside the cylinder with crank angle near the top dead centre. From the figure 9 it is concluded that the temperature rise in initial phase is more for green diesel than petro diesel. The reason behind this is the shorter ignition delay of green diesel due to which fuel burn rate is high in this phase as compared to petro diesel which lead to high temperature. In later stage temperature generated is slightly more for petro diesel. Petro diesel have higher ignition delay which causes long lasting of burning fuel as compared to green diesel

Figure 9: Variation of gas temperature inside the cylinder with crank angle

Conclusion and Recommendations

Green diesel has quality attributes comparable to those of syndiesel, including complete compatibility with petroleum diesel, high energy density, low specific gravity (0.78), excellent storage stability. Results from combustion show shorter ignition delays for green diesel which can overcome the problem of knocking in CI engine. Green diesel has the high cylinder pressure peak as compared to petro-diesel. The peak pressure in case of green diesel was 72.8 bar at 376° crank angle and for petro-diesel was 72.2 bar at 376° crank angle. In India due the poor economic condition and lack of awareness, used oil is not dumped, and is reused for cooking purpose. If the government introduces some program related to awareness of the harmful effect of reusing the used oil and also provides proper waste oil collection system, then there is huge scope to produce bio fuel from waste oil in India also.

Acknowledgement

The author extends his gratitude to all the people who contributed directly or indirectly in bringing out this research to final form, a special thanks to Prof.  Rakesh Kumar.

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