Investigation of a Single Cylinder Diesel Engine Performance under Recycling and Conditioning of Exhaust for Air Intake

Transcription

1 3 th International Conference on AEROSPACE SCIENCES & AVIATION TECHNOLOGY, ASAT- 3, May 6 8, 9, asat@mtc.edu.eg Military Technical College, Kobry Elkobbah, Cairo, Egypt Tel : +() , Fax: +() 698 Paper: ASAT-3-TH-3 Investigation of a Single Cylinder Diesel Engine Performance under Recycling and Conditioning of Exhaust for Air Intake S. E. Elshamarka *, M. A. Elwahhab *, A. M. Rashad *, H. M. A. Elkhalek * Abstract: The exhaust gases of a diesel engine have been conditioned in a recycling process that made it suitable for reuse. The engine thus, is converted into a closed cycle diesel engine (CCDE). The performance of this CCDE is investigated under the prepared synthetic atmosphere. The engine used is a single cylinder air cooled diesel engine (Deutz FL-5), displacement 85 cm 3, 8.3 hp at 5 rpm. The test rig is completely constructed and equipped with all the instrumentation necessary for measuring the parameters needed for the investigation. In addition, a theoretical model is developed to predict the overall performance of a diesel engine operated with normal or synthetic air. Runs are performed in the following conditions: a) Increasing O percentage in an open mode up to 3%, b) Increasing CO percentage in the inlet charge for a closed mode operation. The experimental work is used to verify the theoretical model. The results show that increasing O percentage in the inlet charge leads to increase the rated brake power, decrease the BSFC and increase the BMEP of the engine. Also, the results show that the presence of CO in the inlet charge would have a deleterious effect on the engine performance. Keywords: Closed cycle; diesel engine; synthetic atmosphere; engine performance Abbreviations: AIP Air Independent Propulsion BSFC Brake Specific Fuel Consumption Ca(OH) Calcium Hydroxide CCDE Closed Cycle Diesel Engine CO Carbon dioxide GOX Gaseous Oxygen KOH Potassium Hydroxide I.C.E Internal Combustion Engine IMEP Indicated Mean Effective Pressure LOX Liquid Oxygen NaOH Sodium Hydroxide Oxygen O * Egyptian Armed Forces /

2 . Introduction Diesel engine is an efficient mechanical power generator among all other types of engines. There are many restricted fresh air supply areas, like in mines, caves, under ground installation and, so on, where fresh air is not available for combustion and operating such engines; So, synthetic air is the solution in these areas. G. A. Karime [] experimentally investigated the performance of compression ignition engine in nonconventional atmosphere. He created the synthetic atmosphere by addition of some gases, such as CO or O or N to the intake fresh charge. His study recorded that increasing CO has a strong effect on the delay period, consequently; drop in the output power. But, increasing O content in the intake charge improves the output power. A. Fowler [, 3], developed a hybrid computer simulation for the individual components of the closed cycle diesel engine. The system was constructed and successfully operated. The concentration of CO in the synthetic air was not exceeding - 4% (by volume) to maintain same specific ratio as that of natural air. J G Hawley et al [4, 5], used a 4 cylinder turbocharger diesel engine, after removing the turbocharger to allow the engine to operate naturally-aspirated. Replacing the inert N in air by CO his engine operated purely on (O / CO ) mixture, the engine was being operated with 5% CO (by volume). Other ignition trials were done, where the concentrations of CO reached to 7% and that of O up to 3% (by volume) and the mixture was pre-heated to 5 ºC. H W Wu and C T Shu [6], developed the first CCDE in Taiwan. They studied the engine performance under transient and steady operating conditions. They found that the BSFC decreases as the electric load or the injection pressure increases, and also decreasing when using KOH as CO absorber rather than other absorbents [NaOH, Ca (OH) ]. The oscillation of O at a higher electric load is larger than at a lower electric load.. Theoretical Model The basic concept of the closed cycle diesel engine is relatively simple, but its practical implementation is quite complex, expensive and time consuming. This is due to many different designs and operating variables associated not only with the engine itself but also, with the subsystems used to create and manage the synthetic air loops. Thus, it is decided to develop a model which can be used to predict the overall performance of diesel engines, operated by normal or synthetic air. Input data and output results of the model are shown in Fig. (), by which the performance of the engine operated on open or closed mode were evaluated to save time, effort and cost. /

3 Input data Fuel s chemical composition Inlet synthetic air compositions (by volume) Excess air factor No. of cylinders Speed Compression ratio Thermal Calculations Output data Pressure and Temperature at the end of each stroke IMEP, BMEP, P m Thermal efficiency Fuel consumption (G f, g i, g b ) Power (N i, N b, N m ) Fig. () Input and output data of the model The model is written in (Visual Basic) language for use with any computer, the runs were performed to determine the engine s performance for the following conditions: Operating the engine by natural air on open mode. Increasing and decreasing O percentage in the inlet charge about its normal percentage in the normally aspirated air (% by volume). Operating the engine by synthetic air on closed mode. Then, increasing CO percentage in the inlet charge to 4% (by volume) on the expense of N percentage, under constant O percentage at % (by volume). It is difficult analytically to determine the work performed in an actual cycle, since the losses resulting from each individual process can not be evaluated beforehand for a given engine. In diesel engine, which is used in present research, the value of the excess air factor (α) is varied greatly depending on the load of the engine (from over 5 in small loads to [.3:.5] in full load), so the combustion equation in this case (α > ), can be expressed as: C 6 H 34 + α ε (y O +x CO + (-y-x) N ) θ CO + θ H O+θ 3 N +θ 4 O That equation is used in calculating the pressure and temperature of the mixture during the combustion process. The pressure in the cylinder during admission can be determined assuming steady state process by using the Bernoulli's equation, such as: 3/

4 p in in in gh in p a a is is is gh a By applying the heat balance for a fresh charge and the residual gases before and after mixing, and assuming that the mixing process takes place at constant pressure, we can calculate the temperature at the end of admission process as follow, T a T in T res res T res Hence, the pressure and temperature at the end of compression process are, p com = p a Є n T com = T a Є n - The pressure and temperature at the end of combustion and expansion processes can be calculated as follow, p combustion p com z H l M p T exp exp res U c resu" c n n p com T com res 834T c U" z 834T z Using the previous equations, we can calculate the design indicated work of the whole cycle, as follow: W i. d p com V com n n n n Consequently, calculating the indicated and brake performance of the engine, which characterizes the perfection of the cycle as a utilization of heat and is used to compare between the engine s performances when operated on open or closed modes and varying the concentrations of the inlet charge. 4/

5 3. Experimental Setup and Procedure Figure () shows a schematic drawing for the construction of the test rig and the location of the installed instruments used in this study. The test rig consists of three subsystems (diesel engine coupled with an electric generator, load control system, and exhaust treatment loop. The engine is a 85 cm 3, single cylinder, air cooled, four stroke, direct injection diesel engine (Deutz-FL-5), Table (). In order to produce a synthetic atmosphere, the combustion products which consist of CO, H O, excess O, N and small solid particles (ash and soot) must pass through the treatment loop, to remove the unfavorable constituents from the exhaust flow, and prepare it for mixing with the fresh moderating gases by the suitable percentages. Exhaust gases from the engine flow into the washer to reduce its temperature before entering the scrubber, thus improves the efficiency of the chemical reaction. The cooled gases flow into the absorber as shown in Fig. (3). The main feature of the absorber is the adoption of a simple bubbling method to absorb CO from the exhaust gases by a chemical reaction with a solution of NaOH used as the absorbent with a concentration of 5 % by mass in this study. - Calibrated pipette for fuel flow rate measurement,, 3- Orifice meters for inlet synthetic air and exhaust gases flow rates measurement, 4- Shaft encoder (WDG58B- G4) for engine speed and crank angle measurement, 5- Piezoelectric sensor (PCB-B) for in-cylinder pressure measurement, 6, 7, 8, 9- K type thermocouples for exhaust gases temperature measurement,, - Gas analyzer (UEI Automotive Auto 4-) for exhaust gases and inlet synthetic atmosphere concentrations measurement. Fig. () Layout of the test rig 5/

6 Table () Specifications of the diesel engine Parameter Description Model Deutz FL 5 Combustion chamber Open type Bore mm Stroke 5 mm Displacement 85 cm 3 Compression ratio 7 : Cooling system Air cooling Number of cylinders One - vertical Maximum output 8.3 HP at 5 rpm Injection timing 3 o CA, BTDC Starting Electrical Fig. (3) Assembly drawing of CO absorbing unit 6/

7 NaOH + CO Na CO 3 + H O kj / kg CO After passing through the absorber, the gases pass through the mist separator, in order to protect the mixer, the surge tank and the engine from the corrosion effects due to NaOH vapours. Then, the flow passes through the gas mixing unit which provides spices to the exhaust gases moderating gases from high pressure bottles, in order to produce the required synthetic air by the required concentrations. The fresh gases are stored in high pressure bottles ( bars), and fed to the mixing unit, via a system of control valves (coarse and fine valves) for each bottle. Then the prepared synthetic atmosphere passes into a surge tank, its volume is.56 m 3 (more than times the engine swept volume) in order to obtain more exact concentration to the entire flow, lower pressure oscillation of the added fresh gases and to ensure a steady and uniform flow for the entire synthetic air before entering the engine. The experimental sequence is as follow, all the measuring instruments are calibrated and zero adjusted before the starting of any experiment. Starting the engine must be done on normal air mode, till it reaches to the steady state operation, Turning the mode of operation to the closed mode, via control valves at the inlet and outlet of the engine, and start feeding the treated exhaust by O and CO from high pressure bottles till reaching to the desired inlet charge concentrations, checked by the gas analyzer device at the inlet of the engine. Using ASME Standard committee MFC- M [], for uncertainties in flow measurements, the uncertainties are determined and shown in Table (). Table () Conclusions of the uncertainty of the measured parameters Parameter Uncertainty % Minimum Maximum Comment Temperature..434 High precision Orifice area High precision Synthetic air mass flow rate.8. High precision Fuel consumption Less precision power.46.5 High precision 4. Results and Discussions More than twenty three experiments were carried out to define the load characteristics of the engine at open and closed modes with varying the concentrations of the inlet charge. The experimental work is done in two parts having the same test conditions and constant speed of 5 rpm; the first is operating the engine on open mode for defining the performance of the engine on normal air, with different O percentage in the engine intake. 7/

8 The data acquisition system is used to record the data from the in-cylinder pressure transducer and the crank shaft encoder to trace the cylinder pressure versus crank angle (Φ) for each test. At variable loads, for different inlet charge concentrations, in-cylinder pressure is taken for each of crank angle and average of consecutive engine cycles to have accurate results. These results are used to observe the effect of varying the inlet charge concentration on the combustion process. Figures (4) to (6) show the improvement of the engine's performance due to increase O percentage in the inlet charge from % to 5% by volume on the expense of N concentration and the comparison between the theoretical and experimental results. The reported improvement in the rated brake power of the engine by :3% from idling to full load, as shown in Fig. (6), decreasing the fuel consumption by 7:% from idling to full load, as shown in Fig. (5), are due to increasing the pressure and the temperature inside the cylinder, as shown in Fig. (4) Brake power 7 6 Brake power kw % O 5% O 4% O 3% O % O % O kw % O % O 3% O 4% O 5% O Fig. (4) Theoretical and experimental effect of increasing O on brake power kg / hr Fuel consumption % O % O 3% O 4% O 5% O 3% O kg/hr Fuel consumption % O % O 3% O 4% O 5% O Fig. (5) Theoretical and experimental effect of increasing O on Fuel consumption 8/

9 9 8 7 Combustion pressure 75 7 Combustion pressure MPa % O % O 3% O 4% O 5% O 3% O bar % O % O 3% O 4% O 5% O Fig. (6) Theoretical and experimental effect of increasing O on combustion pressure The second part of experimental work is operating the engine on closed mode, increase CO percentage in the inlet charge to 35% by volume, 8% increment step, with constant O percentage at %. It is noticed that the presence of CO in the intake mixture would have a measurably deleterious effect on the engine's performance in comparison with that achievable on a normal air mixture. In closed mode operation, especially at high loads, the engine becomes more available of the presence of CO which reaches to % by volume in the inlet charge, the degradation in engine performance and the validation of theoretical results can be clearly seen on Figs. (7) to (9). CO absorbs more energy than normal air in order to reach the same final temperature. During the compression stroke it doesn't attain the auto-ignition temperature at the same position of the piston, leads to increase the ignition delay period over that experienced in naturally aspirated conditions, and reduce the reaction rate. Consequently, delays the starting of combustion which leads to incomplete burning of the fuel, reducing the available time for combustion and substantial drop in the max pressure is observed, as shown in Fig. (9), which shows the reduction in the combustion pressure by increasing the CO percentage. The pressure reduction is more noticeable at high loads, as CO percentage increased, when compared to normal air. This leads to increase the exhaust gas temperature, increase the consumed fuel Fig. (8), reduce torque and output brake power Fig. (7) and increase the BSFC. 9/

10 kw Brake power Normal air.5 CCDE CCDE-4% CO.5 CCDE-% CO CCDE-3% CO CCDe-35% CO.5 CCDE-4% CO kw Brake power Normal air CCDE 4% CO % CO 3% CO 35% CO Fig. (7) Theoretical and experimental effect of CCDE and increasing CO on brake power.5 Fuel consumption.8 Fuel consumption.6.4 kg / hr MPa.5 Normal air CCDE CCDE-4%CO.5 CCDE-% CO CCDE-3%CO CCDE-35%CO CCDE-4% CO kg / hr..8 Normal air.6 CCDE.4 4% CO % CO. 3% CO 35% CO Fig. (8) Theoretical and experimental effect of CCDE and increasing CO on fuel consumption Combustion pressure Normal air CCDE CCDE-4% CO CCDE-% CO CCDE-3% CO CCDE-35% CO CCDE-4% CO bar Combustion pressure % O CCDE 4% CO % CO 3% CO 35% CO Fig. (9) Theoretical and experimental effect of increasing CO on combustion pressure in CCDE /

11 By increasing the CO percentage in the inlet charge to 35% by volume, 8% increment step, more degradation in the engine's performance (brake power, BSFC and fuel consumption) are observed for air and synthetic air operation. It can be seen that a reduction of about 4:% of the rated brake power from idling to 8% partial load respectively, increase in the fuel consumption by about :% from idling to 8% partial load. Also, it can be seen that the results of experimental work have the same trend of the theoretical results but there are some discrepancies in some values due to the used coefficients in the theoretical model which needs some correlations and mean that the model is acceptable for presenting the engine's performance for open and closed modes. 5. Conclusions The basic concept of the closed cycle diesel engine is relatively simple, but its practical implementation is quite complex, expensive and time consuming. This is due to many different designs and operating variables associated not only with the engine itself but also, with the subsystems used to create and manage the synthetic air loops. Much attention should be given to well matching of subsystems and sufficient precaution and safety awareness will be taken. From the present work the following could be concluded:. Increasing O percentage leads to increase the released heat from combustion process which transformed into extra work for the engine, translated into enhancing the output performance of the engine as increasing the rated brake power of the engine by :3% from idling to full load, decreasing the BSFC by 5:3%, increasing the BMEP by -5% and decreasing the fuel consumption by 7:% from idling to full load.. Complete closed cycle has been successfully developed; presence of CO in the inlet charge is a thermodynamic problem. CO is a tri-atomic gas; its presence in the inlet charge increases the heat capacity of the mixture, hence decreasing the ratio of specific heats and reducing the temperature and pressure within the cylinder at the end of compression stroke. Operating the engine on closed mode and increasing CO percentage to 35% on the expense of N, at constant O percentage, leads to a lowering the in-cylinder peak pressure by about 5:5% from idling to full load. 3. Theoretical model for calculating thermodynamic properties of the engine has been successfully developed. Modifications to existing model have been improved from experimental work to be successful for predicting the engine's performance whilst operating under air or synthetic air. /

12 6. References [] G. A. Karime, D. E. Gee and R. T. C. Satterford, "Performance of a C.I engine in unconventional atmosphere", Journal of The Engineer, Technical Contributors Section, Vol. 9, pp , March 965. [] A. Fowler, "Hybrid computer simulation and validation of a closed cycle diesel engine", proceedings of UKSC Conference on Computer Simulation, Bath University, pp 38-39, September, 984. [3] A. Fowler, "Underwater power sources", Society for under water Technology, Sub technical 83 Conference, 983. [4] J. G. Hawley, S. J. Ashcroft and M. A. Patrick, "The effects of non- air mixtures on the operation of a diesel engine by experiment and by simulation", proceedings of IMechE, paper A469, Vol., part A, pp 55-67, 998. [5] J. G. Hawley, S. J. Ashcroft and M. A. Patrick, "Diesel engine research for underwater applications", Transaction IMareE, Vol. 6, part, pp 6-75, 993. [6] H. W. Wu, C. T. Shu, "Effects of operating parameters on steady and transient behaviors of a closed cycle diesel engine", Journal of Energy Conversion and Management, Vol. 47, pp 7-8, March 6. [7] R. B. Abernethy, R. P. Benedict and R. B. Dowdell, ASME measurement uncertainty, Journal of Fluids Engineering, Transactions of the ASME, Vol. 7, pp 6-64, June 985. /