Prediction of combustion and emission characteristics ...

The 5th AUN/SEED-Net Regional Conference on New/Renewable Energy STE, HUST, September 26-27, 2012

Prediction of combustion and emission characteristics in a single cylinder common-rail diesel engine enriched by syngas Tran Thi Thu Huong, Nguyen Duc Khanh, Pham Hoang Luong, Le Anh Tuan Hanoi University of Science & Technology E-mail: [email protected]

Abstract The increase of energy demand for transport, industry and personal leads to the sources of fossil fuels are becoming exhausted and found major contributed greenhouse gas emissions by the consumption of these fuels. Hence, a numerous researchers and engine manufacturers worldwide are focused on using alternative fuels for internal combustion engines. Biomass gasification products consist of many compositions such as hydrogen (H2), carbon monoxide (CO), methane (CH4), etc., which is also known as syngas. The effects of syngas addition on common-rail diesel engine combustion and emission characteristics are present in this article by the simulation study on AVL Boost software. The simulation results show that indicated mean effective pressure (IMEP) is increased; ignition delay and combustion duration are slightly shorter; NOx, CO and soot emissions surged with the addition of syngas. When adjusting the diesel flow rates to obtain same IMEP value, the emissions are declined; however, it was still higher than the original engine. With the same engine power output, diesel fuel can be saved about 7.25% with the flow rate of syngas is 0.48 kg/h at 33% load. Keywords: common-rail diesel engine, syngas, biomass gasification, AVL Boost simulation

1. Introduction In recent decades, the exhaust of traditional energy resources such as coal, petroleum oil, etc. leads to the cost for them is higher, effect directly on the world economy. Finding new and renewable energies to replace the fossil energies is the most important mission of scientific researchers over the world [1]. There are a lot of alternative energies are discovered: wind (onshore and offshore), marine (wave and tidal), solar PV, hydrogen from renewable sources, biomass, etc. [2]. Among many energy alternatives, biomass may likely emerge as the most strategically important sustainable energy sources in the foreseeable future. This biomass contribution represents 17 - 30% of projected total energy requirements up to 2050 [3]. About 60% of the needed process energy in pulp, paper, and forest products is provided by biomass combustion [4]. Lignocellulosic biomass is a potential source for second generation ethanol, methanol for Spark Ignition (SI) engines, and

that is not directly linked to food production. For Compression Ignition (CI) engines, the production of biomass gasification (synthesis gas – syngas) can be used to produce Biomass To Liquid (BTL), Gas To Liquid (GTL) ... through Fischer-Tropsch (FT) synthesis, or methanol (to produce Dimethyl Ether – DME) through chemical reactions. Furthermore, synthesis gas is also used for fuel cells and directly combustion for heating [5]. Syngas had been using as an additive fuel for CI engines or the main fuel on SI engines. There are a numerous paper investigated about using syngas on internal combustion engines. C.D. Rakopoulos et al. [6,7] 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. [8] studied the performance and emissions of a SI engine driven generator on biomass based syngas. The experimental is carried out on a commercial 5.5 kW generator modified for operation with

1


100% syngas, the mass flows of this gas are adjusted to obtaining same electrical power with those got for gasoline operation. The CO and NOx emissions are lower, whereas CO2 is significantly higher for the syngas operation. R. G. Papagiannakis et al. [9] evaluated the performance and exhaust emissions of a SI engine operating on syngas as against natural gas at the same lambda (λ) value. The engine power is slightly higher than that of natural gas engines. The brake specific fuel consumption (BSFC) is significant increased. NO and CO emissions concentration are higher for syngas operation. On CI engine, A. S. Ramadhas et al. [10] used producer gas from coir-pith as a supplement fuel for diesel and Rubber seed oil. The brake thermal efficiencies (BTE) are decreased when operating at dual-fuel conditions. The CO and CO2 emissions of dual-fuel engine are 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. [11,12] evaluated the effects of H2/CO ratio on the performance of dual-fuel diesel engine. There are four ratios of H2:CO in syngas fuel, 100:0, 75:25, 50:50 and 0:100. The BTE of dual fuel modes raised with an increase in H2% of syngas composition. The HC, CO and CO2 emissions improved with the increase of CO content in syngas, whereas NOx emission had an opposite trend. R. Uma et al. [13] also used producer gas supplying to a diesel generator engine, the experimental test is conducted at four loads; the concentration of CO, CO2, SO2, HC and particulate matter (PM) are measured. The results showed that BTE reduced in the dual-fuel mode, CO and HC emissions surged, NOx, SO2 and PM declined. In conclusion, the low energy density of the producer gas/air mixture and the engine’s volumetric efficiency are the main factors causing the power de-rating of engines [14]. However, the cost for production same engine power while using biomass is much cheaper than 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 had a positive effect on the environment by using agriculture wastes (rice husk, stover, straw) or forest/wood residues (wood chips, sawdust, coir-pith ...).

Before the experimental stage, predicting the characteristics of dual fuel syngas/diesel engine by using an advanced simulation tool like AVL Boost is always beneficial for analyzing. It provides a higher flexibility in changing parameters, savings in time and money.

2. Simulation models 2.1 Combustion model Mixing Controlled Combustion (MCC) model is used for the prediction of the combustion characteristics of DI diesel engine [15]. The model considers the effects of the premixed (PMC) and diffusion (MCC) controlled combustion processes according to: dQtotal dQPMC dQMCC   d d d

(1)

with dQMCC  Ccomb . f1 mF , QMCC . f 2 k , V  d  dQPMC     QPMC   a .m  1. y m .e a . y m1 d  c

(2)

(3)

The ignition delay is calculated using the Andree and Pachernegg [16] model by solving the following differential equation: dI id TUB  Tref  d Qref

(4)

When the ignition delay integral Iid reaches a value of 1.0 (=at αid) at the ignition delay τid is calculated from τid = αid – αSOI. 2.2 Heat transfer model The heat transfer to the walls of the combustion chamber, the cylinder head, the piston, and the cylinder liner, is calculated from: (5) Qwi  Ai . w .TC  Twi  with αw is heat transfer coefficient, it is calculated by G. Woschni in 1978 [17]. 2.3 Exhaust emission formation model For the calculation of NOx formation in IC engines, a computational program based on a reaction-kinetic model was developed by Pattas and Häfner with 6 reactions (based on the well known Zeldovich mechanism) [18].

2


The concentration of N2O is obtained by the following relation: N 2O   18,71  1,1802.106 T10,6125 exp  N 2 O2  RT 

(6)

The NO formation rate is calculated by Eq. 7:  R R  p d NO  2 1   2  1e  4 e  dt 1  K 2 1  K 4  RT





(7)

Table 1. Specifications of test engine Model Type Bore Stroke Compression ratio Start of Injection Injection pressure

PL1 R2

The CO value can be computed by solving a differential equation based on two reactions and expressing the resulting CO reaction rate as [19]:  CO   d CO   R1  R2 1   dt  CO e 

9 J1 5 10

CL1

2

(9) n1

   .e  

 p O2 dm soot.ox 1 n  Aox . .msoot  2 .  pO ref d  char  2

Ta  form Tave

(10)

n3

  TTa ox  .e ave (11)  

- Aform soot formation factor [-] - Aox soot oxidation factor [-] - τchar characteristic mixing time [0CA] - mfuel mass of fuel burned [kg] - Ta-form activation temp: soot formation [K] - Ta-ox activation temp: soot oxidation [K] - Tave average in-cylinder temperature [K] - pcyl/pref normalized in-cylinder press [-] - pO2/pO2ref normalized oxygen partial press [-] - n1, n2, n3 model factor [-]

6 11 R1

J2

MP1

12 1 PL2

7

MP4

SB2

SB1

Fig. 1. AVL 5402 engine simulation model 3.2 Model calibration The calibration is conducted at an engine speed of 2000 rpm, λ = 1.56, IMEP = 6.35 bar, using only diesel fuel. Fig. 2 and 3 shows the comparison of the pressure curve and CA1050-90 values acquired from experimental and simulation. 90 n = 2000 rpm λ = 1.56 IMEP = 6.35 bar

75

Pressure [bar]

d

p . cyl d diff  p ref

I1 MP3

C1

with dm fuel

8

3

(8)

dm soot dm soot. form dmsoot.ox   d d d

 A form .

E1

4

MP2

with [CO]e is the predicted equilibrium concentration of CO. The soot formation model based on Schubiger et al. [20] used two steps equation approach (formation and oxidation). The net rate of change in soot mass msoot is the difference between the rates of soot formed msoot.form and oxidized msoot.ox.

dm soot. form

AVL 5402 Four-stroke, CI engine 85 mm 90 mm 17.3 200CA before TDC 600 bar

Experimental Simulation

60 45 30 15 0 -180

-120

-60

0

60

120

180

Crank Angle [deg]

3. Simulation setup

Fig. 2. Calibration of in-cylinder pressure 100

3.1 Simulation model building MFB [%]

Based on the structure of real engine and elements attached in AVL Boost software, the simulation model of the test engine can be created, as showed in Fig. 1. The test engine used in this study is the AVL 5402 single cylinder research engine with the specifications are listed in table 1.

Experimental

80

CA90= 46.030

Simuation

60 CA50= 3.680

40 20 CA10= -5.430

0 -180

-120

-60

0

60

120

180

Crank Angle [deg]

Fig. 3. Calibration of CA10-50-90

3


Syngas is the mixture of many components. In this study, syngas defined as a mixture of CO, H2, CO2, CH4 and N2 with the ratio showed in table 2. Table 2. Syngas compositions and properties Properties % by vol. % by mass Mol. weight Density* A/F ratio LHV

CH4 CO H2 N2 CO2 6 29 29 38 8 4.07 34.37 1.62 45.04 14.9 16.04 28.01 2.016 28.01 44.01 0.714 1.25 0.089 1.25 1.964 17.2 2.5 34.3 0 0 50 10.1 120 0 0

* at 00C and 1 atm Based on the data in table 2, properties of syngas can be calculated as follow: - Density : 1.0544 [kg/m3] - Stoichiometric A/F ratio : 2.115 [-] - Low heating value (LHV) : 7.45 [MJ/kg] To estimate the effects of syngas contribution on the combustion and emission characteristics of the test engine, five values of mass flow rates (kg/h) of syngas are used: 0 (case 1), 0.12 (case 2), 0.24 (case 3), 0.36 (case 4) and 0.48 (case 5). In the first condition, the diesel flow rates are fixed at three positions of load (33%, 66% and 100% - full load). In the second condition, the diesel flow rates are adjusted to obtaining the same IMEP value (at three load values) with the addition of syngas. The λ value for dual-fuel engine is calculated as following equation: 

dm Air dmdiesel . A F diesel  dmsyngas . A F syngas

(12)

In this equation, dmAir, dmdiesel and dmsyngas are mass flow rates of intake air, diesel and syngas, respectively [kg/h]; (A/F)diesel and (A/F)syngas are the stoichiometric A/F ratio of diesel and syngas, respectively.

4. Results and Discussion Fig. 4 presents the variation in percentage of IMEP with the adding of syngas at four flow rate (relative with case 1 – original operation). As shown in the Fig. 4, the effect of syngas

10 Case 2 Case 3

8

IMEP increase [%]

3.3 Simulation procedure

addition is most apparent at light load with leaner mixture.

Case 4 Case 5 6

4

2

0 33%

66%

100%

Load position [%]

Fig. 4. The variation of IMEP with the addition of syngas There is a little difference in the combustion start timing and combustion duration. The ignition timing is earlier and combustion duration is shorter than that of the original engine. Fig. 5 illustrates the in-cylinder temperature profiles at different flow rate of syngas at 33% load. The peak value of temperature jumps with the increase of syngas addition. 1900 Case 1 Case 2 Case 3 Case 4 Case 5

1700

Temperature [K]

These figures describe that the simulation results matched with the experimental data. Hence the simulation model can be applied to predict the combustion and emission characteristics of syngas dual-fuel diesel engine.

1500 1300 1100 900 700 -40

-30

-20

-10

0

10

20

30

40

Crank Angle [deg]

Fig. 5. In-cylinder temperature curves with the addition of syngas at 33% load Fig. 6, 7 and 8 demonstrates the accumulated mass of NOx, CO and Soot emissions along with crank angle at 33% load. Due to the syngas consist of CO, CO2, N2, and the reduction dramatically of the λ value, both of CO and soot emissions are increased. Over the engine load, the average increase of the NOx emission is in turn 5.48%, 9.27%, 14.21% and 23.43%; CO emission is in turn 4.92%, 10.71%, 17.24% and 18.37%; soot emission is in turn 8.96%, 18.44%, 28.43% and 43.92% for case 2, case 3, case 4 and case 5, respectively.

4


rates. All the pollution emissions are surged with the addition of syngas at the same performance. The increase of emissions is more apparent at light load and higher mass flow rates of syngas addition.

0.5 Case 1 Case 2 Case 3 Case 4 Case 5

0.3

8 0.2

0.1

0 -40

-30

-20

-10

0

10

20

30

40

Crank Angle [deg]

Fig. 6. Accumulated mass of NOx emission with crank angle at 33% load 0.8

CO mass [mg]

0.6 0.5

0.2 0.1 0 -20

-10

0

10

20

30

40

Crank Angle [deg]

Fig. 7. Accumulated mass of CO emission with crank angle at 33% load 0.1 Case 1 Case 2 Case 3 Case 4 Case 5

Soot mass [mg]

0.08

Case 4

5

Case 5

4 3 2 1

0.04

0.02

5. Summary

0.06

0 -30

-20

9.08

Fig. 9. The percentage change of diesel fuel consumption reduction with syngas addition As shown in table 3, the increase of three main emissions under the same IMEP is lower than that of the first case – same diesel flow rates. It can be explained by the change of the λ value. At the same diesel flow rates, the additions of syngas lead to the λ value reduces dramatically. Whereas, when reducing the diesel flow rates to keep the IMEP, the mixture is leaner. Hence NOx, CO and soot emissions deteriorate in comparison with the first case. Table 3. Average pollution emission reduction with the constant of IMEP (relative to case 1) Emissions NOx CO Soot

-40

6.35

IMEP [bar]

0.3

-30

Case 3 6

3.59

0.4

-40

Case 2

7

0

Case 1 Case 2 Case 3 Case 4 Case 5

0.7

Diesel consumption reduction [%]

NOx mass [mg]

0.4

-10

0

10

20

30

40

Crank Angle [deg]

Fig. 8. Accumulated mass of soot emission with crank angle at 33% load Fig. 9 illustrates the proportion reduction of diesel fuel consumption when the IMEP is constant. When IMEP fixed over the engine load, the diesel fuel consumption declines about 1.23%, 2.05%, 3.48% and 4.37% with the flow rates of syngas addition are 0.12, 0.24, 0.36 and 0.48 kg/h, respectively. Table 3 shows the variation in percentage of three main pollution emissions from the test engine under different loads and syngas flow

Case 2 Case 3 Case 4 Case 5 +0.84% +5.25% +4.40% +8.61% +2.31% +5.64% +7.91% +12.1% +6.31% +14.1% +19.8% +28.6%

The paper presented the simulation results of combustion and emission characteristics of a single cylinder common rail diesel engine enriched by syngas. The addition of syngas from the intake manifold had both of positive and negative effect. The positive effect is IMEP increased; however, the whole of the main emissions are improved. When reducing the diesel flow rate to keep the IMEP, diesel can be saved about 4.37% with the addition of syngas with its flow rate of 0.48 kg/h. The pollution emissions are lower than that of the first case, but it is slight higher than the original engine.

5


Due to these effects of syngas addition and the system equipment, syngas is unsuitable for vehicle engines in the city or other high populated places. This gas can be used for diesel generator in the country and mountain region due to the available of local biomass for syngas production and the place to build downdraft biomass gasifiers; in addition, the cost is much cheaper than the conventional power generation cost.

6. Acknowledgement The authors would like to thank HUST and International Collaboration Protocol project for funding this study. We are grateful for the help and support of Msc. Nguyen The Truc and other staffs at Internal Combustion Engine Lab, STE, HUST.

7. References [1] T. Catal et al., Electricity production from twelve monosaccharides using microbial fuel cells, Journal of Power Sources 175, (2008), pp. 196-200. [2] T.J. Foxon et al., UK innovation systems for new and renewable energy technologies: drivers, barriers and systems failures, Energy Policy 33, (2005), pp. 2123–2137. [3] D.O. Hall, Biomass energy in industrialised countries - a view of the future, Forest Ecology and Management 91, (1997), pp. 1745. [4] H. Chum and R. Overend, Biomass and renewable fuels, Fuel Processing Technology 71, (2001), pp. 187–195. [5] W. Zhang and U. Söderlind, A review on transportation fuels from biomass syngas, 7th World Congress on Recovery, Recycling and Reintegration, Beijing, 2005. [6] C.D. Rakopoulos and C.N. Michos, Development and validation of a multi-zone combustion model for performance and nitric oxide formation in syngas fueled spark ignition engine, Energy Conversion and Management 49, (2008), pp. 2924–2938. [7] C.D. Rakopoulos et al., Availability analysis of a syngas fueled spark ignition engine using a multi-zone combustion model, Energy 33, (2008), pp. 1378– 1398. [8] Ajay Shah et al., Performance and emissions of a spark-ignited engine driven

generator on biomass based syngas, Bioresource Technology 101, (2010), pp. 4656–4661. [9] R.G. Papagiannakis et al., Study of the performance and exhaust emissions of a sparkignited engine operating on syngas fuel, International Journal of Alternative Propulsion, Vol. 1, (2007), pp. 190-215. [10] A.S. Ramadhas et al., Dual fuel mode operation in diesel engines using renewable fuels: Rubber seed oil and coir-pith producer gas, Renewable Energy 33, (2008), pp. 2077– 2083. [11] B.B. Sahoo et al., Effect of H2:CO ratio in syngas on the performance of a dual fuel diesel engine operation, Applied Thermal Engineering, (2011) (in press). [12] B.B. Sahoo et al., Effect of Load Level on the Performance of a Dual Fuel Compression Ignition Engine Operating on Syngas Fuels With Varying H2/CO Content, Journal of Engineering for Gas Turbines and Power 133, (2011), pp. 122802-1–122802-12. [13] R. Uma et al., Emission characteristics of an electricity generation system in diesel alone and dual fuel modes, Biomass and Bioenergy 27, (2004), pp. 195–203. [14] Juan Daniel Martínez et al., Syngas production in downdraft biomass gasifiers and its application using internal combustion engines, Renewable Energy 38, (2012), pp. 1-9. [15] Chmela. F and Orthaber. G, Rate of Heat Release Prediction for Direct Injection Diesel Engines Based on Purely Mixing Controlled Combustion, SAE paper 1999-01-0186. [16] Andree. A and Pachernegg. S.J, Ignition Conditions in Diesel Engines, SAE paper 690253. [17] Woschni. G, A Universally Applicable Equation for the Instantaneous Heat Transfer Coefficient in Internal Combustion Engines, SAE paper 6700931. [18] Pattas and Häfner, Stickoxidbildung bei der ottomotorischen Verbrennung, MTZ 12, (1973), pp. 397-404. [19] A. Onorati et al., 1D Unsteady Flows with Chemical Reactions in the Exhaust DuctSystem of S.I. Engines: Predictions and Experiments, SAE paper 2001-01-0939. [20] R. A. Schubiger et al., Rußbildung und Oxidation bei der dieselmotorischen Verbrennung, MTZ 5, (2002), pp. 342-353.

6