Reduction of Carbon Dioxide Emission from Diesel Engine Fuelled with Plastic Pyrolytic Oil Using Modified Charcoals

Carbon dioxide is one of the greenhouse gases majorly contributing to the global warming and greenhouse effects. Combustion of fossil fuels such as coal, petroleum products and natural gas for power production, transportation and industrial applications produce maximum amount of carbon dioxide. Hence, reduction of CO2 emission is mandated to avoid additional add on to the atmosphere and control global warming. A new low cost carbon trapper using modified charcoals has been designed and tested in a stationary diesel engine for the reduction of carbon dioxide emission and results were reported in this article. Normal wooden charcoal was produced and impregnated with NaOH and KOH. These two modified charcoals, Normal wooden charcoal and commercially purchased activated charcoal were testes individually and compared with each other. Also the effect of amount of different charcoals at 100 grams, 200 grams and 300 grams on carbon dioxide reduction were also tested. The potassium hydroxide (KOH) impregnated wooden charcoal with 300 grams mass shows the best result of 63.92% CO2 reduction at 75% engine load and sodium hydroxide (NaOH) impregnated charcoal shows 62.89% reduction in CO2 at the same engine load due to increased adsorption along with absorption and high porosity.


Introduction
CO2 emission due to the fossil fuel combustion from the anthropogenic sources such as coal combustion in power generation, diesel combustion in transport and power sectors is major reason for radiative energy imbalance and global warming in the earth. This increase in level of CO2 leads to 2°C raise in average global temperature which causes glazier melting, acid rain, adverse climatic changes in the earth surface and pollution of water resources. It is mandatory to reduce the CO2 level on the earth surface for safeguarding the human beings and other living things in the earth from many vulnerable defects. The developed countries in the globe have formed many regulatory bodies and IOP Publishing doi: 10.1088/1757-899X/1130/1/012082 2 stringent emission norms for automotive and power industries to control CO2 emission and other harmful pollutants. Hence it has become mandatory to develop new technological solutions for green house emission capture. There are three major CO2 capturing methods widely recommended for fossil fuel combustion systems namely pre-combustion, oxy-combustion and post-combustion out of which post-combustion is identified as well matured, economic, flexible and effective method. Among the several technologies used, CO2 adsorption technique at ambient and high pressure using activated carbon employed in postcombustion method is most efficient and cost effective with low energy requirement. However the efficiency of this technique is mainly depends on the quality of the adsorbent used. The desired properties of the adsorbent for effective CO2 adsorption are (i) capacity of adsorption at different temperatures (ii) kinetics of adsorption / desorption (iii) stability of adsorption capacity after repeated cycles and (iv) sufficient mechanical strength to withstand high pressure stream. Activated carbon or activated charcoal derived from biomass solid waste such as wood, coconut shell, date seed and walnut shell etc. have been found to be best suitable adsorbents for CO2 capture from engine exhaust gas. To improve the adsorption capacity of the activated carbon its surface needs to be modified by chemical treatments with mineral, chemicals and other materials. Because the CO2 adsorbing capacity of the activated charcoal is mainly based on the porosity of the structure and surface density properties. The adsorbing capacity of the activated carbon can be improved by the impregnation of base solutions on the surface, because of the acidic nature of the CO2. Yong et al. reported that calcium oxide and magnesium oxide impregnation on carbon based adsorbents have been recorded with increased adsorption capacity of 0.22 and 0.28 mmol/g respectively. They also reported that adsorption capacity has been enhanced due to the strong interaction between CO2 and impregnated adsorbent [19]. Somy et al. studied the effect of Cr2O and ZnCO3 impregnated activated carbon on CO2 adsorption and reported that the adsorption capacity has been increased by 25% due to the impregnation [24]. The higher adsorption capacity has been reported for cation impregnated activated carbons in comparison with normal raw activated carbons due to the combined action of physical and chemical adsorption due to metal ion groups [25]. The effect of NaOH, KOH and Na2CO3 impregnated zeolite on the CO2 adsorption was studied and reported by Lillo-Rodenas et al. They reported that Na2CO3 impregnated zeolite showed the better performance. In the present study two base components namely KOH and NaOH are impregnated on the surface of commercially available activated charcoal and tested for the CO2 reduction from the exhaust emission of diesel engine fuelled with plastic pyrolysis oil and results were compared with the normal wooden charcoal and commercially available activated charcoal.

Preparation of plastic oil through pyrolysis
The waste plastics of different kinds collected from various sources were heated to 300 -400°C in absence of oxygen for about 90 minutes in a fixed bed reactor made up of steel of 25 cm diameter, 30 cm long and 0.5 cm wall thickness with electrical heater of 10°C/min rate of rise. Most of the toxic gases are burnt at that high temperature and hot plastic oil will be condensed and collected. Fractional distillation process was used to get the different categories of fuel from the waste plastic oil in further stage. The fatty acid components of plastic pyrolysis oil is presented in the table 1. The physiochemical properties of waste plastic pyrolysis oil are estimated and compared with diesel and given in table 2. The photographic views of crude and distilled plastic pyrolysis oil are shown in figure 1.

Preparation of modified charcoal
The normal wooden charcoal and commercial activated charcoal used in this study were purchased from the local market in Chennai India. The activated carbon was made in to small particles IOP Publishing doi:10.1088/1757-899X/1130/1/012082 3 approximately into 2 mm size and filtered from the dust particles, further it was washed using deionized water and dried in the furnace at 100 °C for about 2 hours. 100 grams of the laboratory grade KOH and NaOH were weighted exactly and thoroughly dissolved in 1000 ml of deionized water. 100 grams of charcoal (1:1 weight ratio) was mixed with alkaline solution. The mixing was performed in a water bath shaker for 60 minutes at room temperature. Then the solution was filtered and impregnated charcoal was dried in the oven at 100 °C for 48 hours [17]. The process flow of impregnation is given in figure 2.    Figure 2. Impregnation process flow.

Design of CO2 capture unit
The CO2 capture unit was designed as two parts namely inner core and outer shell and assembled. The inner core unit was designed for filling the carbon particles in three different mass of 100 grams, 200 grams and 300 grams. Three comportments of steel cylindrical vessels surrounded by wire mesh on top and bottom faces and one small hole with lid on each vessel to fill the charcoal granules were welded 200 mm apart each to make inner core. The outer shell was made by steel pipe of 4 inch diameter as shown in figure 3. The 3D CAD model of CO2 capture unit is shown in figure 4. The photographic views of the unit is shown in figure 5. Each compartment in the inner unit is capable of filling 100 grams of charcoal. For 200 grams test two compartments will be filled and for 300 grams test 3 compartments will be filled and used. The space between two compartments is designed in such a way that the back pressure will not shoot up and affect the engine performance.

Design of CO2 capture unit
The experimental engine setup consists of a 5.2 kW single cylinder, rated speed, direct injection, naturally aspired, water cooled Kirloskar make engine equipped with eddy current dynamometer and load cell. The engine is also coupled with a data acquisition system, pressure, temperature and crank angle position sensor for accurate measurements. Well calibrated AVL 444 digas analyzer and AVL smoke meter are attached in the engine tailpipe for the measurement of CO, CO2, NO, HC and smoke opacity emissions. The schematic diagram of the experimental setup, photographic views of the experimental setup and exhaust gas analyzer are shown in figure 6, figure 7 and figure 8 respectively. The detailed specification of test engine is given in table 3 and accuracy and percentage of uncertainties of different instrument are given in table 4. The total percentage of uncertainty for the instruments is ±1.4%. The engine is started after the confirmation of level of lubricating oil and flow of cooling water circulation. Once the engine attained stability the required engine performance related readings are noted at different loads from 0% to 100% of full load with 25% increment. The repeatability of the engine results are ensured by conducting each trial thrice and average value is considered for further analysis. The effect of each charcoal at different mass proportions on CO2 reduction are analyzed and compared.

Effect of different charcoals on CO2 reduction
The variation of CO2 emission at different loads for plastic oil fuelled diesel engine with and without CO2 capturing unit are compared with that of diesel. The experimental results for three different mass proportions (100 grams, 200 grams and 300 grams) of charcoals filled in the CO2 capturing unit are plotted and shown in figure 9, figure 10 and figure 11 respectively. It is clearly noted from the figures that KOH impregnated charcoal recorded lower CO2 emission than that of other charcoals at all three mass proportions. This is due to that the KOH impregnation on charcoal surface would have enhanced the adsorption process along with the regular absorption of CO2 by charcoals. The NaOH impregnated charcoal recorded second best results at all loads and all mass proportions. The major reason is the base chemical impregnation on the surfaces of charcoals may favours the sorption performance due to the acid nature of CO2 emission. The experiments beyond 300 grams of charcoals are not recorded here due to the increase in stagnation pressure in the capturing unit leads to increase in the back pressure in the tail pipe of the engine which will affect the performance of the engine.

Conclusion
An attempt was made to design and develop a cost effective CO2 capturing system for the reduction of diesel engine CO2 emission with KOH and NaOH impregnated activated charcoal. Experiments were conducted in the single cylinder diesel engine fuelled with plastic pyrolysis oil at different loading conditions to assess the effectiveness of the CO2 trapping system and the following conclusions were made.
• The KOH impregnated charcoal showed highest adsorption capacity followed by NaOH impregnated charcoal at all loading conditions. • The maximum percentage reduction of CO2 is 63.92% recorded for 300 grams of KOH impregnated charcoal at 75% engine load followed by 300 grams of NaOH impregnated charcoal at the same load with 62.89%. • 300 grams mass of charcoal showed better results that other mass proportions at all loading conditions irrespective of type of charcoal.