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Combustion, vibration and noise analysis of hydrogen-diesel dual fuelled engine
Fuel 241 (2019) 488–494
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Combustion, vibration and noise analysis of hydrogen-diesel dual fuelled engine
T
Sarthak Nag, Priybrat Sharma, Arpan Gupta, Atul Dhar
⁎
School of Engineering, Indian Institute of Technology Mandi, 175005, India
ARTICLE INFO
ABSTRACT
Keywords: Hydrogen Dual fuel Combustion characteristics Vibration analysis Combustion noise
The transportation sector of the present-day world is facing severe problems like increasing global pollution and continuous depletion of conventional energy resources; both at alarming rates; which has motivated the researchers to look for alternative fuels and study various aspects of clean burning and sustainable fuels. The vibration of the engines during the combustion is one crucial aspect, as it defines the overall ride quality and comfort of an automobile. In this work, the authors have studied dual fuel combustion using a constant speed diesel engine, operated using hydrogen and diesel. The experimental studies are carried at the load of 25%, 50% and 75% with the substitution of diesel with hydrogen for the energy share of 0%, 5%, 10% and 20%. The effect of hydrogen addition on the combustion characteristics, vibrations and acoustics in the engine is investigated. In this study, marginal pernicious effects of hydrogen addition on the in-cylinder pressure are observed, particularly at lower loads. However, the vibration and noise level sees a reduction with hydrogen addition. The effect of combustion characteristics on noise and vibration parameters is carried out to understand their correspondence. Hydrogen supplementation is found beneficial for noise and vibrations level at low and mid-range loads.
1. Introduction Due to the increasing environmental issues and depletion of natural petroleum resources, the governments across the globe are constantly trying to look for the utilization of alternative fuels for transportation purposes. Researchers are constantly working on various eligible candidates like biodiesel, compressed natural gas (CNG), hydrogen, alcohols, liquefied petroleum gas (LPG) and most recently electricity [1–6]. Among all these candidates, hydrogen is seen as the most suitable alternative fuel due to the variety of methods available to produce it as well as the reduction in emissions it offers on combustion [7,8]. Moreover, hydrogen acts as a combustion enhancer due to its high flame speed, high diffusivity and broader flammability limit [4,9]. But to infrastructural incapability in current world scenario, it is better to take the path of utilization of hydrogen in bi-fuel vehicles, also known as diesel pilot ignited hydrogen combustion, before switching to hydrogen-fuelled internal combustion engines [7]. Diesel engines, owing to their reliability, fuel mileage, robustness and low-end torque, are quite popular in long-haul transportation [10]. But problems like high emission of NOx and other greenhouse gases and high vibrations leads to high pollution as well as driving discomfort and fatigue [11–14]. Vibrations, sometimes ignored, is an essential factor for overall engine performance, passenger comfort and condition ⁎
monitoring [15]. Motion sickness and full body vibrations; which affect the health of the passengers are entirely associated with engine vibrations [16]. Therefore, substitution of some amount of diesel by hydrogen seems to be an exciting study to curb the aforementioned issues. Various studies have been carried on the combustion characteristics of hydrogen in CI engines in the last decade. Lilik et al. conducted experiments on a 2.5 L, 4-cylinder diesel engine by substituting diesel by 0%, 2.5%, 7.5% and 15% hydrogen based on energy share at various loads and speeds. They noted an increase in the maximum in-cylinder pressure, with an elevated effect at higher loads [17]. Szwaja et al. also studied the combustion of hydrogen in diesel engines by injecting the hydrogen in intake manifold using port fuel injector. HES was kept at 0%, 5%, 15% and 25%. They obtained higher in-cylinder pressure on the addition of hydrogen. Moreover, the start of combustion saw a shift from 6 CAD bTDC to 15 CAD bTDC on hydrogen addition [18]. However, Christodoulou et al. reported a low combustion efficiency of hydrogen at low load and low hydrogen fraction [19]. Hence, there is a discrepancy on the effects of H2 energy substitution on combustion characteristics. To seek the reason behind this disagreement, Chintala et al. studied the autoignition of hydrogen-air charge in dual fuel engine and concluded that hydrogen combustion is predominantly affected by the in-cylinder temperature [20]. For the vibrational analysis of the hydrogen-diesel dual fuelled
Corresponding author. E-mail address: [email protected] (A. Dhar).
https://doi.org/10.1016/j.fuel.2018.12.055 Received 1 April 2018; Received in revised form 8 December 2018; Accepted 11 December 2018 0016-2361/ © 2018 Elsevier Ltd. All rights reserved.
Fuel 241 (2019) 488–494
S. Nag et al.
Nomenclature aTDC bTDC CA CI CR EVC EVO FFT H2 HES
IVC IVO kJ kPa MPRR ms RMS RPM STFT TDC θ
After top dead centre, degrees Before top dead centre, degrees Crank angle, degrees Compression ignition Compression ratio Exhaust valve close Exhaust valve open Fast Fourier Transform Hydrogen gas Hydrogen energy share, %
engine, there is an apparent gap in the literature. Negligible attention has been given to the vibration characteristics of the hydrogen diesel engines. However, a few studies on dual fuelled engine’s vibrational and acoustic characteristics have been reported. Recently, Omar et al. carried out the time and frequency analysis of dual fuel engine using LPG-diesel [16]. They took the aid of FFT and STFT for the analysis of the vibrations. Their results showed the low vibrational levels in dual fuel engines as compared to diesel engines. More recently, Satsangi et al. studied the noise and vibration for diesel/n-butanol blends on genset engine and found that the blends show high vibrations at higher loads compared to baseline diesel [11]. Researchers have also studied the vibration of various blends of biodiesel [12]. In their study, B40 and B20 blends have minimum vibrations. The vibrations further reduced by 12% when the engine was serviced. However, no such results and data for the hydrogen addition in diesel engine exist as of authors’ knowledge. Owing to the inconsistency in the literature regarding the effect of hydrogen on combustion characteristics, and the complete gap of the
Table 1 Detailed specification of the test engine. Engine Parameter
Specification
Make and model Engine type Rated power Type of cooling Swept volume Bore × Stroke Clearance volume Compression ratio (CR) Speed Injection pressure Injection timing Injector Angle Diameter of nozzle Number of injector holes Combustion chamber
Kirloskar, Model TV1 Single-cylinder, 4-stroke, CI diesel engine 5.2 kW (7 BHP) @1500 rpm Water cooled 0.661 L 87.5 × 110 mm 40.1 cc 17.5:1 1500 rpm, constant 270 bar at Full Load 23° BTDC 15° with the vertical axis 9.2 mm 3 Hemispherical bowl-in-piston type
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Hydrogen Gas Cylinder Pressure Regulator of Hydrogen Flame Arrestor Hydrogen Mass Flowmeter Needle Valve Hydraulic Seal Hydrogen Injector Air Filter Air Mass Flowmeter Air surge tank Fuel Tank Load Cell for Fuel Measurement
13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
Intake valve close Intake valve open Kilo Joules Kilo Pascal Maximum Pressure Rise Rate Millisecond Root Mean Square Rotations per minute Short-Time Fourier Transform Top dead centre Degree crank angle
Fuel Line Pressure Sensor Diesel Injector Accelerometer In-cylinder Pressure Sensor Optical Encoder Test Engine Transient Dynamometer VFD Drive Test Bed Control System Engine Control System Exhaust Temperature Measurement Data Acquisition and Analysis System
Fig. 1. Schematic diagram of the test setup.
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taken to understand the vibrational signature of the engine. The ringing intensity and combustion noise are also studied at various loads and HES. These values are of great interest as they would encourage the researchers to investigate the hydrogen-diesel dual-fuel engines for better reliability and performance. In a nutshell, this study will supplement the existing combustion knowledge of hydrogen in a diesel engine (dual fuel mode) and will uncover the vibrational and combustion characteristics of the hydrogen diesel dual fuelled engine.
Table 2 Engine Experiment Test Matrix. Load%
Hydrogen Energy Replacement level
Gaseous fuel replacement flow rate required (g/min)
Engine Torque (N-m)
25
0% 5% 10% 20%
0 0.17 0.35 0.7
7.5 7.5 7.5 7.5
50
0% 5% 10% 20%
0 0.23 0.46 0.92
15 15 15 15
75
0% 5% 10% 20%
0 0.3 0.6 1.18
22.5 22.5 22.5 22.5
2. Experimental setup and methods 2.1. Experimental setup A single cylinder, four stroke, water cooled engine which was modified to run in dual fuel mode was used for the experiments. Engine specifications are given in Table 1. This engine was mounted on a universal engine mounting test bed and was coupled to a three-phase asynchronous vectorial servo motor. Variable frequency drive (VFD) controlled the motor, and an industrial programmable logic control (PLC) system controlled the drive for initial starting and loading purposes. Engine crank gear was also modified to mount and couple optical encoder to measure the engine speed and crank rotation of the crankshaft. Fig. 1 shows the schematic diagram of the experimental setup. Port fuel injection of hydrogen and direct injection of diesel was
vibration and acoustic study of the hydrogen-diesel dual fuelled engines, this study focuses on the impact of hydrogen on the engine combustion and vibrational characteristics. Therefore, the impact of hydrogen substitution on combustion characteristics, heat release rates, vibrational characteristics and combustion noise is reported in this study. Further, for the vibrational studies, the aid of FFT and STFT is
Fig. 2. Cylinder pressure and heat release rate as a function of CAD at (a) 25% load; (b) 50% load; and (c) 75% load. 490
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Fig. 3. (a) Combustion noise; and (b) Normalized ringing intensity; as a function of load for various HES.
done to achieve dual fuel combustion in the setup. Hydrogen was supplied from 130 bar pressurised industrial gas cylinder, which was reduced to 3 bars using a double-stage pressure regulator. For the safety measures, two flashback arrestors (Messers, DG91N) were used, one just after double-stage pressure regulator and another before port fuel injector. Additionally, a hydraulic seal was installed in the hydrogen supply line, serving the dual purpose of safety and flow fluctuation damping. Needle valves were used to control the flow of hydrogen through the system safely. A Coriolis mass flow meter (Bronkhorst, Mini CORI-FLOW M14) is used to detect and log the mass flow rate of hydrogen gas. On the engine end, port fuel injector (AFS Gs-60-05-5H) was mounted on the intake manifold, and hydrogen injection was timed using an in-house developed engine control and data acquisition system. The diesel fuel tank was placed on a shear-beam type load cell (Sensortronics, 65089) to obtain and record gravimetric diesel consumption. The engine air intake was fitted with a 200 L air-box, airfilter, orifice plate and manometer arrangement to dampen the airflow oscillations and measure air consumption rate. The diesel engine was equipped with an in-cylinder pressure sensor (Kistler, 6045B) with a range of 0 to 250 bars for accurate combustion monitoring. The head of the engine was modified to fit in the cylinder pressure sensor. A fuel line pressure transducer (Kistler, 4067E) was mounted on the 6 mm fuel line after boring a 1.5 mm hole in the line. The single axis accelerometer (PCB Piezotronics, 352C03) was suitably mounted on the head of the cylinder. The combustion and vibration data was then collected and stored using data acquisition system (National Instruments, 9411; 9223).
HES =
mhydrogen LCVhydrogen (1)
mhydrogen LCVhydrogen + mdiesel LCVdiesel
() g s
where LCVhydrogen = 120 × and mhydrogen , mdiesel are fuel mass flow rates. At engine load of 25, 50 and 75%, HES is increased from 0 to 5, 10 and 20% as shown in Table 2. Managing dynamometer torque allows loading of the engine and managing hydrogen flow rate enables control of HES. All the measurements were performed after the test point attains stability, starting with in-cylinder and fuel line pressure data, followed by acceleration data. For the analysis of the vibration signal acquired using the accelerometer, mathematical tools like RMS, FFT and STFT were carried out. The RMS value is given by the Eq. (2) kJ 103 Kg
N x (n ) 2 n= 1
RMS =
N
(2)
where x(n) is the discrete signal and n is the number of samples acquired n = 1,2, 3… N terms. The FFT of the signal was computed using Eq. (3). N
x (n ) e (
X (k ) = n=1
i2 nk )/ N
(3)
2.2. Experimental methods In this study, the engine was run at a constant speed of 1500 RPM, while the engine load and hydrogen energy share (HES) was varied. The engine has a valve overlap period of 9° CAD after IVO till EVC at 4.5° aTDC. So the hydrogen injection was started at 14.5° aTDC with a margin of 10° CAD for safety. Even though the total available injection duration was 190° CAD till IVC but throughout the experimentation, hydrogen injection period was kept constant to 90° CAD (10 ms @1500 RPM), i.e. till 75.5° bBDC. Such injection strategy allows for the maximum hydrogen to enter the cylinder with assured reliability. The hydrogen line had an injection pressure of 3 bar and the needle valve placed after the flame trap was used to control the flow rate of hydrogen. The HES is calculated using Eq. (1).
Fig. 4. RMS acceleration and maximum pressure rise rate as a function of HES at loads of 25%, 50% and 75%. 491
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Fig. 5. Frequency spectrum of vibrations (g) produced in engine head at (a) 25% load; (b) 50% load; and (c) 75% load.
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HES 5%
HES 10%
HES 20%
Load 75%
Load 50%
Load 25%
Diesel
Fig. 6. 20 kHz short time–frequency analysis of vibrations produced in engine head at various loads and hydrogen energy share.
where k = 1,2, 3… N terms. The STFT of the same signal x(n) is given by the Eq. (4).
S (k , m) =
x (n ) W ( k
n) e (
and 50% with hydrogen substitution. Such findings are synchronous with the findings reported by Zhou et al. The dip in the peak pressure was due to the poor combustion efficiency exhibited by hydrogen at lower loads [23]. HRR curves for load 25% and 50% shows retardation of premixed combustion peak. At the load of 75%, improved combustion efficiency is exhibited by hydrogen due to the increase in bulk temperature inside the cylinder. Moreover, the HRR has a noticeable increase at 75% load case. The peak pressure also shows a noticeable increase with hydrogen substitution for 75% load (6560 kPa, 6616 kPa, 6638 kPa and 6680 kPa for HES 0%, 5%, 10% and 20% respectively).
i2 mn )/ N
n=
(4)
where W(n) is the window function and m is the discrete frequency variable. The ringing intensity, an acoustic metric gives the tendency to knock [21,22]. The Eq. (5) presents the mathematical formula for calculation of ringing intensity.
RI
1 2
where
quency,
(( ) ) dP dt max
Pmax
2
RTmax
3.2. Combustion noise and ringing intensity
(5)
Combustion noise was calculated using the cylinder pressure data. Fig. 3(a) shows the combustion noise for various loads at varying HES. The combustion noise level for loads of 25% and 50% decreases with an increase in hydrogen substitution levels due to a decrease in cylinder pressure. But the noise levels increase tremendously for 75% engine load due to the active participation of hydrogen in combustion. Similar trends are noticeable for the ringing intensity (RI). RI is based on acoustic energy flux produced by oscillating pressure and gives the measure of knock [24]. The tendency of knocking decreases for 25% and 50% load on the substitution of hydrogen, but increases for 75% load. Due to the high in-cylinder bulk temperature, multiple local heat spot formation leads to higher knocking tendency. Visible pressure aberrations can be seen on the cylinder pressure plot at Fig. 2(c).
is the specific heat ratio,
( )
dP dt max Tmax is
1/4f , where f = oscillating freis the maximum pressure rate rise, Pmax is the peak
pressure, the temperature corresponding to peak pressure and R is the gas constant. 3. Results and Discussion 3.1. Combustion characteristics
The cylinder pressure data was measured using the in-cylinder pressure sensor. Fig. 2(a), (b) and (c) illustrates the variation of cylinder pressure and heat release rate with crank angle. The maximum pressures of 5225 kPa, 5109 kPa, 5053 kPa and 4978 kPa were measured for the load of 25% at HES of 0%, 5%, 10% and 20% respectively. A similar gradual decrease in pressure with hydrogen substitution was observed for 50% load. The similar trends follow for heat release rate metric. The peak pressure positions also showed a noticeable delay for loads of 25%
3.3. Vibrational analysis Fig. 4 shows the variation of the RMS value of acceleration and MPRR with varying HES at various loads. RMS acceleration decreases 493
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with increase in HES for loads of 25% and 50%. This decrease can be correlated with the reduced combustion efficiency of hydrogen at lower loads. A similar trend observed for the maximum value of the rate of pressure rise for these loads. However, at the load of 75%, the increase in MPRR value increases the acceleration after the initial dip up to 5% HES. Hence it can be concluded that the improvement in combustion efficiency of hydrogen tends to increase the vibrations in the engine. Fig. 5 shows the frequency spectrum of the vibration signal. For the load of 25% (Fig. 5(a)), the amplitude vibration at 875 Hz decreases with the substitution of hydrogen in an engine. The decrease can be directly correlated with the reduction of in-cylinder pressure on the addition of hydrogen (Fig. 2(a)). A similar pattern can be observed for 50% load condition (Fig. 5(b)) where the peak of 875 Hz decreases with hydrogen substitution too. However, for 75% load, the peak of 875 Hz shows an increase in vibration amplitude with hydrogen substitution. All these findings indicate that hydrogen combustion tends to increase the vibrations in the dual fuelled engine. The vibration data is in complete agreement with the cylinder pressure variation. Moreover, this also shows that the combustion frequency of the hydrogen diesel powered engine is 875 Hz. Since humans are more susceptible to frequencies below 1000 Hz [15], hydrogen substitution may cause more discomfort in the real-time conditions. Fig. 6 shows the 20 kHz short time–frequency analysis of vibrations produced in engine head at various hydrogen energy share for 25%, 50% and 75% load, respectively. The vibrations caused in the engine head due to valve opening and closures are also visible at CAD of −356°, −144°, 144° and 355°. STFT confirms that the higher frequency and magnitude vibrations are caused due to the combustion.
at Indian Institute of Technology Mandi, India. References [1] Emiroğlu AO, Şen M. Combustion, performance and emission characteristics of various alcohol blends in a single cylinder diesel engine. Fuel 2018;212:34–40. [2] Lin C-Y, Lin S-A. Effects of emulsification variables on fuel properties of two-and three-phase biodiesel emulsions. Fuel 2007;86:210–7. [3] Singh AP, Agarwal AK, Agarwal RA, Dhar A, Shukla MK. Introduction of alternative fuels. Prospect Altern Transp Fuels 2018:3–6. Springer. [4] Tripathi G, Nag S, Dhar A, Patil DV. Fuel Injection Equipment (FIE) Design for the New-Generation Alternative Fuel-Powered Diesel Engines Singapore: Springer; 2018. p. 387–405. https://doi.org/10.1007/978-981-10-7518-6_16. [5] Yu X, Du Y, Sun P, Liu L, Wu H, Zuo X. Effects of hydrogen direct injection strategy on characteristics of lean-burn hydrogen–gasoline engines. Fuel 2017;208:602–11. https://doi.org/10.1016/J.FUEL.2017.07.059. [6] Sharma P, Dhar A. Effect of hydrogen supplementation on engine performance and emissions. Int J Hydrogen Energy 2018;43:7570–80. https://doi.org/10.1016/J. IJHYDENE.2018.02.181. [7] Verhelst S, Wallner T. Hydrogen-fueled internal combustion engines. Prog Energy Combust Sci 2009;35:490–527. https://doi.org/10.1016/J.PECS.2009.08.001. [8] Tomita E, Kawahara N, Piao Z, Fujita S, Hamamoto Y. Hydrogen Combustion and Exhaust Emissions Ignited with Diesel Oil in a Dual Fuel Engine, 2001. doi:10.4271/ 2001-01-3503. [9] Bhasker JP, Porpatham E. Effects of compression ratio and hydrogen addition on lean combustion characteristics and emission formation in a Compressed Natural Gas fuelled spark ignition engine. Fuel 2017;208:260–70. https://doi.org/10.1016/ J.FUEL.2017.07.024. [10] Johnson TV. Diesel emissions in review. SAE Int J Engines 2011;4. https://doi.org/ 10.4271/2011-01-0304. 2011-01–0304. [11] Satsangi DP, Tiwari N. Experimental investigation on combustion, noise, vibrations, performance and emissions characteristics of diesel/n-butanol blends driven genset engine. Fuel 2018;221:44–60. https://doi.org/10.1016/J.FUEL.2018.02.060. [12] Taghizadeh-Alisaraei A, Ghobadian B, Tavakoli-Hashjin T, Mohtasebi SS. Vibration analysis of a diesel engine using biodiesel and petrodiesel fuel blends. Fuel 2012;102:414–22. https://doi.org/10.1016/J.FUEL.2012.06.109. [13] World Energy Outlook 2014. IEA; 2014. doi:10.1787/weo-2014-en. [14] Wang M. The Greenhouse Gases, Regulated Emissions and Energy Use in Transportation (GREET) Model 1999. [15] Wongchai B, Visuwan P, Chuepeng S. The vibration analysis of diesel engine with hydrogen-diesel dual fuel. Am J Appl Sci 2013;10814:8–14. https://doi.org/10. 3844/ajassp.2013.8.14. [16] Omar FK, Selim MYE, Emam SA. Time and frequency analyses of dual-fuel engine block vibration. Fuel 2017;203:884–93. https://doi.org/10.1016/J.FUEL.2017.05. 034. [17] Lilik GK, Zhang H, Herreros JM, Haworth DC, Boehman AL. Hydrogen assisted diesel combustion. Int J Hydrogen Energy 2010;35:4382–98. https://doi.org/10. 1016/J.IJHYDENE.2010.01.105. [18] Szwaja S, Grab-Rogalinski K. Hydrogen combustion in a compression ignition diesel engine. Int J Hydrogen Energy 2009;34:4413–21. https://doi.org/10.1016/J. IJHYDENE.2009.03.020. [19] Christodoulou F, Megaritis A. Experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine. Int J Hydrogen Energy 2013;38:10126–40. https://doi.org/10.1016/J.IJHYDENE. 2013.05.173. [20] Chintala V, Subramanian KA. Experimental investigation of autoignition of hydrogen-air charge in a compression ignition engine under dual-fuel mode. Energy 2017;138:197–209. https://doi.org/10.1016/J.ENERGY.2017.07.068. [21] Maria A, Cheng WK, Kar K, Cannella W. Understanding knock metric for controlled auto-ignition engines. SAE Int J Engines 2013;6. https://doi.org/10.4271/2013-011658. 2013-01-1658. [22] Dernotte J, Dec JE, Ji C. Energy distribution analysis in boosted HCCI-like/LTGC engines – understanding the trade-offs to maximize the thermal efficiency. SAE Int J Engines 2015;8. https://doi.org/10.4271/2015-01-0824. 2015-01-0824. [23] Zhou JH, Cheung CS, Leung CW. Combustion, performance, regulated and unregulated emissions of a diesel engine with hydrogen addition. Appl Energy 2014;126:1–12. https://doi.org/10.1016/J.APENERGY.2014.03.089. [24] Wildman C, Scaringe RJ, Cheng W. On the Maximum Pressure Rise Rate in Boosted HCCI Operation, SAE Technical Paper, 2009. doi:https://doi.org/10.4271/200901-2727.
4. Conclusions Combustion characteristics along with noise and vibration analysis of the hydrogen-diesel dual fuelled engine were studied experimentally in this article. The value of hydrogen based on the energy share was varied in the sets of 0%, 5%, 10% and 20%. The in-cylinder pressure and engine vibration were measured at different engine loads. The major conclusions from this study were:
• As the HES is increased from 0% to 20%, the peak pressure de• •
creased by 4.7% for 25% and 50% load conditions but increased by 2% for 75% load. This was due to improved hydrogen combustion efficiency at higher loads. The tendency of knocking also decreases with hydrogen supplementation for lower loads but increases at higher loads. Vibrations in the engine also increase due to the active participation of hydrogen in the combustion, but this phenomenon is observed at higher loads. At lower loads, the vibrations are quite moderate.
Acknowledgments The authors gratefully acknowledge the research funding and support provided by the Department of Science and Technology-Science and Engineering Research Board, Government of India vide Project No. ECR/2015/000135 titled “Study of Synergistic Use of Hydrogen and other Alternative Fuels in a Dual Fuel Engine for Emissions Reduction”
494
Contents lists available at ScienceDirect
Fuel journal homepage: www.elsevier.com/locate/fuel
Full Length Article
Combustion, vibration and noise analysis of hydrogen-diesel dual fuelled engine
T
Sarthak Nag, Priybrat Sharma, Arpan Gupta, Atul Dhar
⁎
School of Engineering, Indian Institute of Technology Mandi, 175005, India
ARTICLE INFO
ABSTRACT
Keywords: Hydrogen Dual fuel Combustion characteristics Vibration analysis Combustion noise
The transportation sector of the present-day world is facing severe problems like increasing global pollution and continuous depletion of conventional energy resources; both at alarming rates; which has motivated the researchers to look for alternative fuels and study various aspects of clean burning and sustainable fuels. The vibration of the engines during the combustion is one crucial aspect, as it defines the overall ride quality and comfort of an automobile. In this work, the authors have studied dual fuel combustion using a constant speed diesel engine, operated using hydrogen and diesel. The experimental studies are carried at the load of 25%, 50% and 75% with the substitution of diesel with hydrogen for the energy share of 0%, 5%, 10% and 20%. The effect of hydrogen addition on the combustion characteristics, vibrations and acoustics in the engine is investigated. In this study, marginal pernicious effects of hydrogen addition on the in-cylinder pressure are observed, particularly at lower loads. However, the vibration and noise level sees a reduction with hydrogen addition. The effect of combustion characteristics on noise and vibration parameters is carried out to understand their correspondence. Hydrogen supplementation is found beneficial for noise and vibrations level at low and mid-range loads.
1. Introduction Due to the increasing environmental issues and depletion of natural petroleum resources, the governments across the globe are constantly trying to look for the utilization of alternative fuels for transportation purposes. Researchers are constantly working on various eligible candidates like biodiesel, compressed natural gas (CNG), hydrogen, alcohols, liquefied petroleum gas (LPG) and most recently electricity [1–6]. Among all these candidates, hydrogen is seen as the most suitable alternative fuel due to the variety of methods available to produce it as well as the reduction in emissions it offers on combustion [7,8]. Moreover, hydrogen acts as a combustion enhancer due to its high flame speed, high diffusivity and broader flammability limit [4,9]. But to infrastructural incapability in current world scenario, it is better to take the path of utilization of hydrogen in bi-fuel vehicles, also known as diesel pilot ignited hydrogen combustion, before switching to hydrogen-fuelled internal combustion engines [7]. Diesel engines, owing to their reliability, fuel mileage, robustness and low-end torque, are quite popular in long-haul transportation [10]. But problems like high emission of NOx and other greenhouse gases and high vibrations leads to high pollution as well as driving discomfort and fatigue [11–14]. Vibrations, sometimes ignored, is an essential factor for overall engine performance, passenger comfort and condition ⁎
monitoring [15]. Motion sickness and full body vibrations; which affect the health of the passengers are entirely associated with engine vibrations [16]. Therefore, substitution of some amount of diesel by hydrogen seems to be an exciting study to curb the aforementioned issues. Various studies have been carried on the combustion characteristics of hydrogen in CI engines in the last decade. Lilik et al. conducted experiments on a 2.5 L, 4-cylinder diesel engine by substituting diesel by 0%, 2.5%, 7.5% and 15% hydrogen based on energy share at various loads and speeds. They noted an increase in the maximum in-cylinder pressure, with an elevated effect at higher loads [17]. Szwaja et al. also studied the combustion of hydrogen in diesel engines by injecting the hydrogen in intake manifold using port fuel injector. HES was kept at 0%, 5%, 15% and 25%. They obtained higher in-cylinder pressure on the addition of hydrogen. Moreover, the start of combustion saw a shift from 6 CAD bTDC to 15 CAD bTDC on hydrogen addition [18]. However, Christodoulou et al. reported a low combustion efficiency of hydrogen at low load and low hydrogen fraction [19]. Hence, there is a discrepancy on the effects of H2 energy substitution on combustion characteristics. To seek the reason behind this disagreement, Chintala et al. studied the autoignition of hydrogen-air charge in dual fuel engine and concluded that hydrogen combustion is predominantly affected by the in-cylinder temperature [20]. For the vibrational analysis of the hydrogen-diesel dual fuelled
Corresponding author. E-mail address: [email protected] (A. Dhar).
https://doi.org/10.1016/j.fuel.2018.12.055 Received 1 April 2018; Received in revised form 8 December 2018; Accepted 11 December 2018 0016-2361/ © 2018 Elsevier Ltd. All rights reserved.
Fuel 241 (2019) 488–494
S. Nag et al.
Nomenclature aTDC bTDC CA CI CR EVC EVO FFT H2 HES
IVC IVO kJ kPa MPRR ms RMS RPM STFT TDC θ
After top dead centre, degrees Before top dead centre, degrees Crank angle, degrees Compression ignition Compression ratio Exhaust valve close Exhaust valve open Fast Fourier Transform Hydrogen gas Hydrogen energy share, %
engine, there is an apparent gap in the literature. Negligible attention has been given to the vibration characteristics of the hydrogen diesel engines. However, a few studies on dual fuelled engine’s vibrational and acoustic characteristics have been reported. Recently, Omar et al. carried out the time and frequency analysis of dual fuel engine using LPG-diesel [16]. They took the aid of FFT and STFT for the analysis of the vibrations. Their results showed the low vibrational levels in dual fuel engines as compared to diesel engines. More recently, Satsangi et al. studied the noise and vibration for diesel/n-butanol blends on genset engine and found that the blends show high vibrations at higher loads compared to baseline diesel [11]. Researchers have also studied the vibration of various blends of biodiesel [12]. In their study, B40 and B20 blends have minimum vibrations. The vibrations further reduced by 12% when the engine was serviced. However, no such results and data for the hydrogen addition in diesel engine exist as of authors’ knowledge. Owing to the inconsistency in the literature regarding the effect of hydrogen on combustion characteristics, and the complete gap of the
Table 1 Detailed specification of the test engine. Engine Parameter
Specification
Make and model Engine type Rated power Type of cooling Swept volume Bore × Stroke Clearance volume Compression ratio (CR) Speed Injection pressure Injection timing Injector Angle Diameter of nozzle Number of injector holes Combustion chamber
Kirloskar, Model TV1 Single-cylinder, 4-stroke, CI diesel engine 5.2 kW (7 BHP) @1500 rpm Water cooled 0.661 L 87.5 × 110 mm 40.1 cc 17.5:1 1500 rpm, constant 270 bar at Full Load 23° BTDC 15° with the vertical axis 9.2 mm 3 Hemispherical bowl-in-piston type
1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
Hydrogen Gas Cylinder Pressure Regulator of Hydrogen Flame Arrestor Hydrogen Mass Flowmeter Needle Valve Hydraulic Seal Hydrogen Injector Air Filter Air Mass Flowmeter Air surge tank Fuel Tank Load Cell for Fuel Measurement
13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
Intake valve close Intake valve open Kilo Joules Kilo Pascal Maximum Pressure Rise Rate Millisecond Root Mean Square Rotations per minute Short-Time Fourier Transform Top dead centre Degree crank angle
Fuel Line Pressure Sensor Diesel Injector Accelerometer In-cylinder Pressure Sensor Optical Encoder Test Engine Transient Dynamometer VFD Drive Test Bed Control System Engine Control System Exhaust Temperature Measurement Data Acquisition and Analysis System
Fig. 1. Schematic diagram of the test setup.
489
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taken to understand the vibrational signature of the engine. The ringing intensity and combustion noise are also studied at various loads and HES. These values are of great interest as they would encourage the researchers to investigate the hydrogen-diesel dual-fuel engines for better reliability and performance. In a nutshell, this study will supplement the existing combustion knowledge of hydrogen in a diesel engine (dual fuel mode) and will uncover the vibrational and combustion characteristics of the hydrogen diesel dual fuelled engine.
Table 2 Engine Experiment Test Matrix. Load%
Hydrogen Energy Replacement level
Gaseous fuel replacement flow rate required (g/min)
Engine Torque (N-m)
25
0% 5% 10% 20%
0 0.17 0.35 0.7
7.5 7.5 7.5 7.5
50
0% 5% 10% 20%
0 0.23 0.46 0.92
15 15 15 15
75
0% 5% 10% 20%
0 0.3 0.6 1.18
22.5 22.5 22.5 22.5
2. Experimental setup and methods 2.1. Experimental setup A single cylinder, four stroke, water cooled engine which was modified to run in dual fuel mode was used for the experiments. Engine specifications are given in Table 1. This engine was mounted on a universal engine mounting test bed and was coupled to a three-phase asynchronous vectorial servo motor. Variable frequency drive (VFD) controlled the motor, and an industrial programmable logic control (PLC) system controlled the drive for initial starting and loading purposes. Engine crank gear was also modified to mount and couple optical encoder to measure the engine speed and crank rotation of the crankshaft. Fig. 1 shows the schematic diagram of the experimental setup. Port fuel injection of hydrogen and direct injection of diesel was
vibration and acoustic study of the hydrogen-diesel dual fuelled engines, this study focuses on the impact of hydrogen on the engine combustion and vibrational characteristics. Therefore, the impact of hydrogen substitution on combustion characteristics, heat release rates, vibrational characteristics and combustion noise is reported in this study. Further, for the vibrational studies, the aid of FFT and STFT is
Fig. 2. Cylinder pressure and heat release rate as a function of CAD at (a) 25% load; (b) 50% load; and (c) 75% load. 490
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Fig. 3. (a) Combustion noise; and (b) Normalized ringing intensity; as a function of load for various HES.
done to achieve dual fuel combustion in the setup. Hydrogen was supplied from 130 bar pressurised industrial gas cylinder, which was reduced to 3 bars using a double-stage pressure regulator. For the safety measures, two flashback arrestors (Messers, DG91N) were used, one just after double-stage pressure regulator and another before port fuel injector. Additionally, a hydraulic seal was installed in the hydrogen supply line, serving the dual purpose of safety and flow fluctuation damping. Needle valves were used to control the flow of hydrogen through the system safely. A Coriolis mass flow meter (Bronkhorst, Mini CORI-FLOW M14) is used to detect and log the mass flow rate of hydrogen gas. On the engine end, port fuel injector (AFS Gs-60-05-5H) was mounted on the intake manifold, and hydrogen injection was timed using an in-house developed engine control and data acquisition system. The diesel fuel tank was placed on a shear-beam type load cell (Sensortronics, 65089) to obtain and record gravimetric diesel consumption. The engine air intake was fitted with a 200 L air-box, airfilter, orifice plate and manometer arrangement to dampen the airflow oscillations and measure air consumption rate. The diesel engine was equipped with an in-cylinder pressure sensor (Kistler, 6045B) with a range of 0 to 250 bars for accurate combustion monitoring. The head of the engine was modified to fit in the cylinder pressure sensor. A fuel line pressure transducer (Kistler, 4067E) was mounted on the 6 mm fuel line after boring a 1.5 mm hole in the line. The single axis accelerometer (PCB Piezotronics, 352C03) was suitably mounted on the head of the cylinder. The combustion and vibration data was then collected and stored using data acquisition system (National Instruments, 9411; 9223).
HES =
mhydrogen LCVhydrogen (1)
mhydrogen LCVhydrogen + mdiesel LCVdiesel
() g s
where LCVhydrogen = 120 × and mhydrogen , mdiesel are fuel mass flow rates. At engine load of 25, 50 and 75%, HES is increased from 0 to 5, 10 and 20% as shown in Table 2. Managing dynamometer torque allows loading of the engine and managing hydrogen flow rate enables control of HES. All the measurements were performed after the test point attains stability, starting with in-cylinder and fuel line pressure data, followed by acceleration data. For the analysis of the vibration signal acquired using the accelerometer, mathematical tools like RMS, FFT and STFT were carried out. The RMS value is given by the Eq. (2) kJ 103 Kg
N x (n ) 2 n= 1
RMS =
N
(2)
where x(n) is the discrete signal and n is the number of samples acquired n = 1,2, 3… N terms. The FFT of the signal was computed using Eq. (3). N
x (n ) e (
X (k ) = n=1
i2 nk )/ N
(3)
2.2. Experimental methods In this study, the engine was run at a constant speed of 1500 RPM, while the engine load and hydrogen energy share (HES) was varied. The engine has a valve overlap period of 9° CAD after IVO till EVC at 4.5° aTDC. So the hydrogen injection was started at 14.5° aTDC with a margin of 10° CAD for safety. Even though the total available injection duration was 190° CAD till IVC but throughout the experimentation, hydrogen injection period was kept constant to 90° CAD (10 ms @1500 RPM), i.e. till 75.5° bBDC. Such injection strategy allows for the maximum hydrogen to enter the cylinder with assured reliability. The hydrogen line had an injection pressure of 3 bar and the needle valve placed after the flame trap was used to control the flow rate of hydrogen. The HES is calculated using Eq. (1).
Fig. 4. RMS acceleration and maximum pressure rise rate as a function of HES at loads of 25%, 50% and 75%. 491
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Fig. 5. Frequency spectrum of vibrations (g) produced in engine head at (a) 25% load; (b) 50% load; and (c) 75% load.
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HES 5%
HES 10%
HES 20%
Load 75%
Load 50%
Load 25%
Diesel
Fig. 6. 20 kHz short time–frequency analysis of vibrations produced in engine head at various loads and hydrogen energy share.
where k = 1,2, 3… N terms. The STFT of the same signal x(n) is given by the Eq. (4).
S (k , m) =
x (n ) W ( k
n) e (
and 50% with hydrogen substitution. Such findings are synchronous with the findings reported by Zhou et al. The dip in the peak pressure was due to the poor combustion efficiency exhibited by hydrogen at lower loads [23]. HRR curves for load 25% and 50% shows retardation of premixed combustion peak. At the load of 75%, improved combustion efficiency is exhibited by hydrogen due to the increase in bulk temperature inside the cylinder. Moreover, the HRR has a noticeable increase at 75% load case. The peak pressure also shows a noticeable increase with hydrogen substitution for 75% load (6560 kPa, 6616 kPa, 6638 kPa and 6680 kPa for HES 0%, 5%, 10% and 20% respectively).
i2 mn )/ N
n=
(4)
where W(n) is the window function and m is the discrete frequency variable. The ringing intensity, an acoustic metric gives the tendency to knock [21,22]. The Eq. (5) presents the mathematical formula for calculation of ringing intensity.
RI
1 2
where
quency,
(( ) ) dP dt max
Pmax
2
RTmax
3.2. Combustion noise and ringing intensity
(5)
Combustion noise was calculated using the cylinder pressure data. Fig. 3(a) shows the combustion noise for various loads at varying HES. The combustion noise level for loads of 25% and 50% decreases with an increase in hydrogen substitution levels due to a decrease in cylinder pressure. But the noise levels increase tremendously for 75% engine load due to the active participation of hydrogen in combustion. Similar trends are noticeable for the ringing intensity (RI). RI is based on acoustic energy flux produced by oscillating pressure and gives the measure of knock [24]. The tendency of knocking decreases for 25% and 50% load on the substitution of hydrogen, but increases for 75% load. Due to the high in-cylinder bulk temperature, multiple local heat spot formation leads to higher knocking tendency. Visible pressure aberrations can be seen on the cylinder pressure plot at Fig. 2(c).
is the specific heat ratio,
( )
dP dt max Tmax is
1/4f , where f = oscillating freis the maximum pressure rate rise, Pmax is the peak
pressure, the temperature corresponding to peak pressure and R is the gas constant. 3. Results and Discussion 3.1. Combustion characteristics
The cylinder pressure data was measured using the in-cylinder pressure sensor. Fig. 2(a), (b) and (c) illustrates the variation of cylinder pressure and heat release rate with crank angle. The maximum pressures of 5225 kPa, 5109 kPa, 5053 kPa and 4978 kPa were measured for the load of 25% at HES of 0%, 5%, 10% and 20% respectively. A similar gradual decrease in pressure with hydrogen substitution was observed for 50% load. The similar trends follow for heat release rate metric. The peak pressure positions also showed a noticeable delay for loads of 25%
3.3. Vibrational analysis Fig. 4 shows the variation of the RMS value of acceleration and MPRR with varying HES at various loads. RMS acceleration decreases 493
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with increase in HES for loads of 25% and 50%. This decrease can be correlated with the reduced combustion efficiency of hydrogen at lower loads. A similar trend observed for the maximum value of the rate of pressure rise for these loads. However, at the load of 75%, the increase in MPRR value increases the acceleration after the initial dip up to 5% HES. Hence it can be concluded that the improvement in combustion efficiency of hydrogen tends to increase the vibrations in the engine. Fig. 5 shows the frequency spectrum of the vibration signal. For the load of 25% (Fig. 5(a)), the amplitude vibration at 875 Hz decreases with the substitution of hydrogen in an engine. The decrease can be directly correlated with the reduction of in-cylinder pressure on the addition of hydrogen (Fig. 2(a)). A similar pattern can be observed for 50% load condition (Fig. 5(b)) where the peak of 875 Hz decreases with hydrogen substitution too. However, for 75% load, the peak of 875 Hz shows an increase in vibration amplitude with hydrogen substitution. All these findings indicate that hydrogen combustion tends to increase the vibrations in the dual fuelled engine. The vibration data is in complete agreement with the cylinder pressure variation. Moreover, this also shows that the combustion frequency of the hydrogen diesel powered engine is 875 Hz. Since humans are more susceptible to frequencies below 1000 Hz [15], hydrogen substitution may cause more discomfort in the real-time conditions. Fig. 6 shows the 20 kHz short time–frequency analysis of vibrations produced in engine head at various hydrogen energy share for 25%, 50% and 75% load, respectively. The vibrations caused in the engine head due to valve opening and closures are also visible at CAD of −356°, −144°, 144° and 355°. STFT confirms that the higher frequency and magnitude vibrations are caused due to the combustion.
at Indian Institute of Technology Mandi, India. References [1] Emiroğlu AO, Şen M. Combustion, performance and emission characteristics of various alcohol blends in a single cylinder diesel engine. Fuel 2018;212:34–40. [2] Lin C-Y, Lin S-A. Effects of emulsification variables on fuel properties of two-and three-phase biodiesel emulsions. Fuel 2007;86:210–7. [3] Singh AP, Agarwal AK, Agarwal RA, Dhar A, Shukla MK. Introduction of alternative fuels. Prospect Altern Transp Fuels 2018:3–6. Springer. [4] Tripathi G, Nag S, Dhar A, Patil DV. Fuel Injection Equipment (FIE) Design for the New-Generation Alternative Fuel-Powered Diesel Engines Singapore: Springer; 2018. p. 387–405. https://doi.org/10.1007/978-981-10-7518-6_16. [5] Yu X, Du Y, Sun P, Liu L, Wu H, Zuo X. Effects of hydrogen direct injection strategy on characteristics of lean-burn hydrogen–gasoline engines. Fuel 2017;208:602–11. https://doi.org/10.1016/J.FUEL.2017.07.059. [6] Sharma P, Dhar A. Effect of hydrogen supplementation on engine performance and emissions. Int J Hydrogen Energy 2018;43:7570–80. https://doi.org/10.1016/J. IJHYDENE.2018.02.181. [7] Verhelst S, Wallner T. Hydrogen-fueled internal combustion engines. Prog Energy Combust Sci 2009;35:490–527. https://doi.org/10.1016/J.PECS.2009.08.001. [8] Tomita E, Kawahara N, Piao Z, Fujita S, Hamamoto Y. Hydrogen Combustion and Exhaust Emissions Ignited with Diesel Oil in a Dual Fuel Engine, 2001. doi:10.4271/ 2001-01-3503. [9] Bhasker JP, Porpatham E. Effects of compression ratio and hydrogen addition on lean combustion characteristics and emission formation in a Compressed Natural Gas fuelled spark ignition engine. Fuel 2017;208:260–70. https://doi.org/10.1016/ J.FUEL.2017.07.024. [10] Johnson TV. Diesel emissions in review. SAE Int J Engines 2011;4. https://doi.org/ 10.4271/2011-01-0304. 2011-01–0304. [11] Satsangi DP, Tiwari N. Experimental investigation on combustion, noise, vibrations, performance and emissions characteristics of diesel/n-butanol blends driven genset engine. Fuel 2018;221:44–60. https://doi.org/10.1016/J.FUEL.2018.02.060. [12] Taghizadeh-Alisaraei A, Ghobadian B, Tavakoli-Hashjin T, Mohtasebi SS. Vibration analysis of a diesel engine using biodiesel and petrodiesel fuel blends. Fuel 2012;102:414–22. https://doi.org/10.1016/J.FUEL.2012.06.109. [13] World Energy Outlook 2014. IEA; 2014. doi:10.1787/weo-2014-en. [14] Wang M. The Greenhouse Gases, Regulated Emissions and Energy Use in Transportation (GREET) Model 1999. [15] Wongchai B, Visuwan P, Chuepeng S. The vibration analysis of diesel engine with hydrogen-diesel dual fuel. Am J Appl Sci 2013;10814:8–14. https://doi.org/10. 3844/ajassp.2013.8.14. [16] Omar FK, Selim MYE, Emam SA. Time and frequency analyses of dual-fuel engine block vibration. Fuel 2017;203:884–93. https://doi.org/10.1016/J.FUEL.2017.05. 034. [17] Lilik GK, Zhang H, Herreros JM, Haworth DC, Boehman AL. Hydrogen assisted diesel combustion. Int J Hydrogen Energy 2010;35:4382–98. https://doi.org/10. 1016/J.IJHYDENE.2010.01.105. [18] Szwaja S, Grab-Rogalinski K. Hydrogen combustion in a compression ignition diesel engine. Int J Hydrogen Energy 2009;34:4413–21. https://doi.org/10.1016/J. IJHYDENE.2009.03.020. [19] Christodoulou F, Megaritis A. Experimental investigation of the effects of separate hydrogen and nitrogen addition on the emissions and combustion of a diesel engine. Int J Hydrogen Energy 2013;38:10126–40. https://doi.org/10.1016/J.IJHYDENE. 2013.05.173. [20] Chintala V, Subramanian KA. Experimental investigation of autoignition of hydrogen-air charge in a compression ignition engine under dual-fuel mode. Energy 2017;138:197–209. https://doi.org/10.1016/J.ENERGY.2017.07.068. [21] Maria A, Cheng WK, Kar K, Cannella W. Understanding knock metric for controlled auto-ignition engines. SAE Int J Engines 2013;6. https://doi.org/10.4271/2013-011658. 2013-01-1658. [22] Dernotte J, Dec JE, Ji C. Energy distribution analysis in boosted HCCI-like/LTGC engines – understanding the trade-offs to maximize the thermal efficiency. SAE Int J Engines 2015;8. https://doi.org/10.4271/2015-01-0824. 2015-01-0824. [23] Zhou JH, Cheung CS, Leung CW. Combustion, performance, regulated and unregulated emissions of a diesel engine with hydrogen addition. Appl Energy 2014;126:1–12. https://doi.org/10.1016/J.APENERGY.2014.03.089. [24] Wildman C, Scaringe RJ, Cheng W. On the Maximum Pressure Rise Rate in Boosted HCCI Operation, SAE Technical Paper, 2009. doi:https://doi.org/10.4271/200901-2727.
4. Conclusions Combustion characteristics along with noise and vibration analysis of the hydrogen-diesel dual fuelled engine were studied experimentally in this article. The value of hydrogen based on the energy share was varied in the sets of 0%, 5%, 10% and 20%. The in-cylinder pressure and engine vibration were measured at different engine loads. The major conclusions from this study were:
• As the HES is increased from 0% to 20%, the peak pressure de• •
creased by 4.7% for 25% and 50% load conditions but increased by 2% for 75% load. This was due to improved hydrogen combustion efficiency at higher loads. The tendency of knocking also decreases with hydrogen supplementation for lower loads but increases at higher loads. Vibrations in the engine also increase due to the active participation of hydrogen in the combustion, but this phenomenon is observed at higher loads. At lower loads, the vibrations are quite moderate.
Acknowledgments The authors gratefully acknowledge the research funding and support provided by the Department of Science and Technology-Science and Engineering Research Board, Government of India vide Project No. ECR/2015/000135 titled “Study of Synergistic Use of Hydrogen and other Alternative Fuels in a Dual Fuel Engine for Emissions Reduction”
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