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Joumal ofScience & Technology 100 (2014) 036-041 Simulation of a Syngas - Diesel Dual Fuel Engine for Small-Scale Power Generator Le Anh Tuan *, Pham Hoang Luong Hanoi University ofScience and Technology No 1, Dai Co Viet Str., Hai Ba Trung, Ha Noi, Viet Nam Received: September 17 2013; accepted: April 22, 2014 Abstract The paper presents findings from numerical simulation on utilization of syngas in cylinder diesel engine, 8.75 kW power, used in a small gen-set, based on the concept of syngas-dieset dua! fuel It is the first step of the process of applying syngas produced by biomass gasification system to the diesel gen-set to be used in rural areas The simulation model was created on AVL Boost software, of which Vibe zone combustion model was used for the prediction of combustion characteristics, Woschni 1978 was selected for heat transfer model, while NOx, CO and soot emission calculation was based on models developed by Pattas & Hefner, Onoiati and Schubiger, respectively With the constant rates of the syngas containing of 11.63%, H2, 24.47% CO, 01%, CH4, 0.08%, O2, 1.79%, CO2 and 62 02%, N2, the simulation results show that at the engine spe 1500 rpm and indicated mean effective pressure, IfvlEP = 6.54 bar (at the full load condition), the syngas could replace upto 60% of diesel fuel consumption The specific energy consumption increased and exhaust emissions including CO and NOx were raised while soot emission decreased with the syngas quantity of the dual fuel cases Keywords: Syngas-diesel dual fuel, Small d ^1 gen-set, Biomass gasification, AVL Boost simulation Introduction The gasification technology is i kind of thermochemical technologies that can efficiently destroy biomass and generate synthesis gas in a very short time [I] The products of this process consist of ash and synthesis gas which can be applied both heating and power production purpose (mechanical and electricity power) [2] In case of power production purpose, the intemal combustion engine has been considered for integrating with gasification system in small scale power plant (< MW) that can be beneficial in the areas like islands, mral areas, industrial areas, etc [3] Syngas has been using as an additive fuel for compression ignition engines (CI engines) or the main fiiel on spark ignition engines (SI engines) There are a numerous paper investigated about using syngas on intemal combustion engines C D Rakopoulos et al [4,5] investigated the performance and NO emission formation of a SI engine fueled with syngas under various loads by using a multi-dimension combustion model Ajay Shah et al [6] studied the performance and emissions of a SI engine driven generator on biomass based syngas The experiment was earned out on a commercial 5,5 kW generator modified for " Corresponding author; Tel,: (•f84) 4386.3176 Email- tu an leanh@hust edu.vn Operation with 100% syngas, the mass flows of this gas were adjusted to obtaining same electrical power with those got for gasoline operation The CO and NOx emissions were lower, whereas CO2 was significantly higher for the syngas operation R G Papagiannakis et al [7] evaluated the perfonnance and cxhausi emissions of a SI engine operating on syngas and natural gas at the same lambda (X) value The engine power was slightly higher than that of natural gas engines The brake specific fuel consumption (BSFC)' was significant increased NO and CO emissions concentiation were higher for syngas operation On CI engme, A S Ramadhas et al [8] used producer gas from coir-pith as a supplement fuel for diesel and rubber seed oil The brake thermal efficiencies (BTE) were decreased when operatmg at dual fuel conditions The CO and C O : emissions of dual fuel engine were higher than that of the original engine; the smoke density had the same trends with the addition of coir-pith producer gas, B B Sahoo et al [9,10] evaluated the effects of H2/CO ratio on the performance of dual fuel diesel engine There were four ratios of H2:C0 in syngas fiiel, 100:0, 75:25, 50:50 and 0:100 The BTE of dual fuel modes raised with an increase in HiVo of syngas composition The HC, CO and CO2 emissions improved with the increase of CO content in syngas, whereas NOx emission had an opposite tiend Journal ofScience & Technology 100 (2014) 036-041 R Uma et al [ I I ] also used producer gas supplying to a diesel generator engine The experimental results showed that BTE reduced in the dual fuel mode, CO and HC emissions surged, while NOx, SO2 and PM emissions declined The low energy density of the producer gas/air mixture and the engine's volumetnc efficiency are the main factors causing the engine's power derating [12] Besides, the cost for production same engine power while using biomass is much cheaper than that of the conventional diesel engine Hence, using dual fuel syngas-diesel mode is one of the ways to reduce the expense per unit of engine power In addition, the gasification of biomass has a positive effect on the environment by using agriculture wastes (rice husk, rice straw) or forest/wood residues (wood chips, sawdust, coir-pith ,) This paper focuses on numerical study of a cylinder diesel engine, 8.75 kW max power, used in a small gen-set which is operated with single diesel fuel and syngas-diesel dual fuel modes It is aimed to investigate the diesel replacement potential by syngas as well as effects of syngas-diesel dual fiiel modes to combustion characteristics, engine's performance and exhaust behaviors Model Setup And Parameterization 2.1 Engine Specifications The test engine used in this study is the S3L2, cylinder diesel engine with the specifications listed in table I Table ! Specifications of the test engine Model Type Bore Stroke Compression ratio Actual power/speed S3L2 Four-stioke, CI engine 78 mm 92 mm 22:1 8.75 kW/I500 rpm This engine is located in 12 kVA small gen-set The max power at 1500 rpm of this engine at brand new condition is 9.6 kW Of the cunent status, it was measured as 8.75 kW at 1500 rpm, 2.2 Simulation Model and Procedure The simulation model of the test engine was created on AVL Boost It is showed in Fig I The combustion model used is the Vibe zone which has the same input as for the single Vibe function However, instead of one mass averaged temperature, two temperatures (burned and imbumed zone) are calculated The rate of heat release, and thus the mass fraction burned, is specified by a Vibe function However the assumption that bumed and unbiuned charges have the same temperature is dropped Instead the first law of thermodynamics is applied to the bumed charge and unbumed charge, respectively [14] Fig The simulation model 'Il^=-p^^+^dTUu uu 2^-l-hJ/^-hBB.b^^ dVu '^ iia "'' (I) (2) "" index b: bumed zone index u: unbumed zone The term ' i u ~ T ^ covers the enthalpy flow from the unbumed to the bumed zone due to the conversion of a fresh charge to combustion products Heat flux between the two zones is neglected In addition the sum of the volume changes must be equal to the cylinder volume change and the sum of the zone volumes must be equal to the cylinder volume da da Vi,+K = da (3) t4) The heat tiansfer to the walls of the combustion chamber is calculated by: Qi (5) Qm and A, are wall heat flow and surface area (cylinder head, piston, liner), respectively; «„ is heat transfer coefficient, is calculated by Woschni in 1978 model [14]; Tc and T^, are gas temperahire in the cylinder and wall temperature The NOx formation in CI engines is calculated based on a reaction-kinetic model developed by Pattas Journal ofScience & Tecbnology 100 (2014) 036-041 and Hafher [15] The concentiatton of N2O is obtained by the following relation: J ^ N,40, l.lSOS.lO-r-expi^ -Hr (6) The NO formation rate is calculated by: 20%, 30% to 60% while syngas was supphed (dieselsyngas dual fuel) to the intake manifold aiming to maintain the indicated mean effective pressure (IMEP = 6.54bar) The engme performance, combustion charactenstics and exhaust emissions were investigated to evaluate the potential of diese] replacement by syngas 2.3 Syngas dt if, K, RT (7) The CO value can be computed by solving a differential equation based on two reactions and expressing the resulting CO reaction rate as [16]' dCO * R ^ R, I ' CO CO (8) with [CO]e is the predicted equilibrium concentration of CO The soot foimation model based on Schubiger et al [17] used two steps equation approach (formation and oxidation) The net rate of change in soot mass msooi is the difference between the rates of soot formed msooiform and oxidized m^ooi.oxdm ,
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