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Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode
Fuel 87 (2008) 3591–3599
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Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode N. Saravanan *, G. Nagarajan, G. Sanjay, C. Dhanasekaran, K.M. Kalaiselvan Department of Mechanical Engineering, Internal Combustion Engineering Division, College of Engineering, Guindy, Anna University, Chennai 600 025, India
a r t i c l e
i n f o
Article history: Received 25 January 2008 Received in revised form 4 July 2008 Accepted 8 July 2008 Available online 3 August 2008 Keywords: Hydrogen Port injection Diethyl ether Dual fuel Emission
a b s t r a c t Hydrogen is expected to be one of the most important fuels in the near future to meet the stringent emission norms. In this experimental investigation, the combustion analysis was done on a direct injection (DI) diesel engine using hydrogen with diesel and hydrogen with diethyl ether (DEE) as ignition source. The hydrogen was injected through intake port and diethyl ether was injected through intake manifold and diesel was injected directly inside the combustion chamber. Injection timings for hydrogen and DEE were optimized based on the performance, combustion and emission characteristics of the engine. The optimized timing for the injection of hydrogen was 5° CA before gas exchange top dead center (BGTDC) and 40° CA after gas exchange top dead center (AGTDC) for DEE. From the study it was observed that hydrogen with diesel results in increased brake thermal efficiency by 20% and oxides of nitrogen (NOx) showed an increase of 13% compared to diesel. Hydrogen-DEE operation showed a higher brake thermal efficiency of 30%, with a significant reduction in NOx compared to diesel. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The internal combustion engines have already become an indispensable and integral part of our present day life. In recent days the importance of environment and energy are emphasized in various energy schemes [1]. Increase in stringent environment regulations on exhaust emissions and anticipation of the future depletion of world wide petroleum reserves provide strong encouragement for research on alternate fuels [2]. Hydrogen is one of the most promising alternate fuels. It’s clean burning characteristics and better performance drives more interest in hydrogen fuel [3]. Many researchers have used hydrogen as a fuel in spark ignition (SI) engine [4]. A significant reduction in power output was observed while using hydrogen in SI engine In addition pre ignition, backfire and knocking problems were observed at high load. These problems have resulted in using hydrogen in SI engine within a limited operation range [5,6]. However hydrogen cannot be used as a sole fuel in a compression ignition (CI) engine, since the compression temperature is not enough to initiate the combustion due to its higher self-ignition temperature [7]. Hence an ignition source is required while using it in a CI engine. The simplest method of using hydrogen in a CI engine is to run in the dual fuel mode with diesel as the main fuel or Diethyl Ether can be used that can act as an ignition source for hydrogen. In a dual fuel engine the main fuel is either inducted/carburated or injected into the intake air stream with combustion initiated by diesel. The major energy is obtained from diesel while the rest of the energy is supplied by hydrogen. * Corresponding author. Tel.: +91 9881128166. E-mail address: [email protected] (N. Saravanan). 0016-2361/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2008.07.011
The hydrogen operated dual fuel engine has the property to operate with lean mixtures at part load and no load, which results in NOx reduction, with an increase in thermal efficiency thereby reducing the fuel consumption. It was also observed that hydrogen could be substituted for diesel up to 38% on volume basis without loss in thermal efficiency, however with a nominal power loss. Hydrogen used in the dual fuel mode with diesel by Masood et al. [8] showed the highest brake thermal efficiency of 30% at a compression ratio of 24.5. Lee et al. [9] studied the performance of dual injection hydrogen fueled engine by using solenoid in-cylinder injection and external fuel injection technique. An increase in thermal efficiency by about 22% was noted for dual injection at low loads and 5% at high loads compared to direct injection. Lee et al. [10] suggested that in dual injection, the stability and maximum power could be obtained by direct injection of hydrogen. However the maximum efficiency could be obtained by the external mixture formation in hydrogen engine. Das et al. [11] have carried out experiments on continuous carburation, continuous manifold injection, timed manifold injection and low pressure direct cylinder injection. The maximum brake thermal efficiency of 31.32% was obtained at 2200 rpm with 13 Nm torque. Hashimoto et al. [12] have done extensive experimental investigation with DEE and diesel used as ignition source for igniting hydrogen fuel. Table 1 shows the properties of hydrogen in comparison with diesel and DEE. Fig. 1 shows the photograph of hydrogen and DEE flow arrangements. Electronic injectors for hydrogen can have a greater control over the injection timing and injection duration with quicker response to operate under high-speed conditions [13]. The advantage of hydrogen injection over carburated system is problems like
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Nomenclature J/° kg/h kW mm cm3
CI SI ECU DFC IR NRV DSO LPM UBHC NOx CO BTDC CA HHR
Joules per degree kilograms per hour kilowatts millimeter cubic centimeter
Abbreviations PPM parts per million DEE diethyl ether BSN Bosch smoke number TDC top dead center BGTDC before gas exchange top dead center CAD crank angle duration DI direct injection
Table 1 Properties of hydrogen in comparison with diesel and DEE Sl. No. 1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17
Properties
Diesel
Hydrogen
DEE
Formula Auto ignition temperature (K) Minimum ignition energy (mJ) Flammability limits (volume % in air) Stoichiometric air fuel ratio on mass basis Molecular weight (g mol) Limits of flammability (equivalence ratio) Density at 160 C and 1.01 bar (kg/m3) Net heating valve MJ/kg Flame velocity (cm/s) Quenching gap in NTP air (cm) Diffusivity in air (cm2/s Octane number Research Motor Cetane number Boiling point (K) Viscosity at 15.5 °C, centipoise Vapour pressure at 38 °C kPa Specific gravity
CnH1.8nC8–C20 530 – 0.7–5
H2 858 0.02 4–75
C2H5OC2H5 433 – 1.9–36.0
14.5
34.3
11.1
170 –
2.016 0.1–7.1
74 –
833–881
0.0838
713
42.5 30 – –
119.93 265–325 0.064 0.63
33.9 – – –
30 – 40–55 436–672 2.6–4.1 Negligible 0.83
130 – – 20.27 – – 0.091
– – >125 307.4 0.023 110.3 –
backfire and pre ignition can be eliminated with proper injection timing [14]. The photographic view of the hydrogen injector position on the cylinder head is shown in Fig. 2 and the photographic view of the hydrogen and DEE injector position on the intake manifold is shown in Fig. 3. Fig. 4 shows the cross sectional view of the hydrogen injector. The distinguished feature of hydrogen-operated engine is that it does not produce major pollutants such as hydrocarbon (HC), carbonmonoxide (CO), sulphur dioxide (SO2), lead, smoke, particulate matter, ozone and other carcinogenic compounds. This is due to the absence of carbon and sulphur in hydrogen. However hydrogen-operated engines suffer from the drawback of higher NOx emissions that has an adverse effect on the environment. The formation of NOx could be due to the presence of nitrogen in the fuel and air and also the availability of oxygen in the air. In the case of hydrogen it is obvious that NOx is due to the nitrogen present in air [15]. When the combustion temperature is high some portion of nitrogen present in the air reacts with oxygen to form NOx. One of the ways of reducing NOx is to operate the hydrogen engine with lean mixtures. Lean mixture results in lower temperature that would slower the chemical reaction, which weakens the kinetics
compression ignition spark ignition electronic control unit digital mass flow controller infra red non-return valve digital storage oscilloscope liters per minute unburned hydro carbons nitrogen oxides carbon monoxide before top dead center crank angle heat release rate
of NOx formation [16,17]. NOx emissions increase with increase in equivalence ratio and peaks at an equivalence ratio of 0.9. The objective of the present work is to use hydrogen (by injection in the intake port) in the following ways and study the performance, combustion and emission characteristics and compare with baseline diesel: 1. Hydrogen in the dual fuel mode with diesel. 2. Hydrogen with diethyl ether as an ignition source. 2. Experimental setup and procedure The test engine used was a single cylinder water-cooled DI diesel engine, having a rated power of 3.7 kW that runs at a constant speed of 1500 rpm which was modified to work with hydrogen in the dual fuel mode. The specifications of the test engine are given in Table 2. Fig. 5 shows the schematic view of the experimental setup. The flow diagram for hydrogen and DEE is shown in Fig. 6. The fuel injector was controlled by means of an electronic control unit (ECU). An Infrared detector was used to give signals to the ECU for injector opening based on the preset timing and also to control the duration of injection. The injection timing and injection duration can be varied with the help of ECU. Hydrogen flow was taking place based on the preset value. A pressure regulator as well as a digital mass flow controller controlled the flow. Table 3 shows the technical specifications of the hydrogen injector. In the experimental investigation first the injection timing and injection duration for hydrogen were optimized. For this injection timing from 5° CA before ignition top dead center (BITDC) to 25° CA after ignition top dead center (AITDC) in steps of 5° CA was taken with hydrogen injection duration of 30° CA. 60° CA and 90° CA at a constant hydrogen flow rate of 5.5 liters per minute. The next step in the investigation was optimizing the hydrogen flow. For this hydrogen was varied from 1.5 liters per minute to 9 liters per minute insteps of 1.5 liters per minute for the entire load conditions. The optimized conditions for hydrogen based on the performance, emission and combustion characteristics are as follows. Hydrogen injection timing 5° BGTDC. Hydrogen injection duration 30° CA. Hydrogen flow rate 7.5 liters per minute. 3. Instrumentation An electrical dynamometer with 10 kW capacity with a current rating of 43.5 A was used as a loading device. A non-dispersive infra red (NDIR) type exhaust gas analyzer (Qrotech make) was used
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Fig. 3. Photographic view of the hydrogen and DEE injector position on the intake manifold.
Fig. 1. Photographic view of the hydrogen and DEE flow arrangement.
Fig. 4. Cross sectional view of the hydrogen injector.
Fig. 2. Photographic view of the hydrogen injector position on the cylinder head.
for the measurement of HC, CO, NO and CO2 emissions. Technovision analyzer was used for the measurement of NO2 emission. NOx emission was determined by adding NO and NO2 emissions. Bosch type smoke meter was used to measure smoke intensity. The exhaust gases were filtered and dehumidified by the exhaust gas analyzer before measurement. The gas analyzer was calibrated by passing a known amount of span gases and readings were taken with variation in span gas concentration. If the deviations are outside the accuracy limits the analyzer was calibrated by adjusting the knob for the specific gases. The cylinder pressure was measured using a piezoelectric pressure transducer which has a pressure range of 250 bar and a charge amplifier and the pressure data were given as input to the oscilloscope for further analysis. A Kistler make crank angle encoder with an accuracy of 1° was used for crank angle measurement. After 30 min of engine running on stabilized condition the pressure data were collected. The pressure data’s were collected for 1000 cycles by using Yokogawa data acquisition system. The mass flow of hydrogen was measured
using a digital mass flow controller, which controlled and measured the flow in liters per minute. The engine was operated at a constant speed of 1500 rpm at all loads with torques corresponding to full load percentages. 4. Error analysis and estimation of uncertainity All measurements of physical quantities are subject to uncertainties. Uncertainty analysis is needed to prove the accuracy of the experiments. In order to have reasonable limits of uncertainty for a computed value an expression was derived as follows:
"
DR ¼
oR Dx1 ox1
2
þ
oR Dx2 ox2
2
þ þ
oR Dxn oxn
2 #1=2 ð1Þ
Using Eq. (1) the uncertainty in the computed values such as brake power, brake thermal efficiency and fuel flow measurements were estimated. The measured values such as speed, fuel time, voltage and current were estimated from their respective uncertainties based on the Gaussian distribution. The uncertainties in the measured parameters, voltage (DV) and current (DI), method, were ±10 V and ±0.16 A, respectively. For fuel time (Dtr) and fuel
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Table 2 Engine specifications Make and model General details Number of cylinders Bore Stroke Rated speed Swept volume Clearance volume Compression ratio Rated output Injection pressure Fuel injection timing Type of combustion Lubricating oil Connecting rod length
Kirloskar, AV1 make Four stroke, compression ignition, constant speed, vertical, water-cooled, direct injection. One 80 mm 110 mm 1500 rpm 553 cc 36.87 cc 16.5:1 3.7 kW at 1500 rpm 205 bar 23° BTDC Hemispherical open combustion chamber SAE 20 W40 235 mm
Therefore, the uncertainty in the brake power from Eq. (2) is ±0.1929 kW and the uncertainty limits in the calculation of B.P are 4.4 ± 0.1929 kW. The percentage of uncertainty for the measurement of speed, mass flow rate, NOx, hydrocarbon, smoke and pressure is given below: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii)
Speed: 1.5. Mass flow rate of air: 1.9. Mass flow rate of diesel: 2.1. Mass flow of hydrogen: 1.8. NOx: 2.7. Hydrocarbon: 3.2. Smoke: 2.0. Pressure: 3.2.
5. Results and discussion Experiments were carriedout with hydrogen and diesel in dual fuel operation and with DEE. The engine was not able run beyond 75% load in hydrogen DEE mode due to severe knocking. This is attributed to the instantaneous combustion of both hydrogen and DEE. The numerical values of the results are given in Appendix. 6. Performance characteristics
1. Hydrogen cylinder 2. Pressure regulator 3. Hydrogen tank 4. Filter 5. Digital mass flow controller 6. PC to control DFC 7. Flame trap 8. Flame arrester 9. Hydrogen injector
10. IR sensor for hydrogen 11. Electronic control unit for H2 12. Engine 13. Dynamometer 14. Diesel tank 15. DEE fuel pump 16. DEE Electronic control unit 17. DEE Injector 18. IR sensor for DEE
Fig. 5. Schematic view of the experimental setup.
volume (Dt), the uncertainties were taken as ±0.2 s and ±0.1 s, respectively. A sample calculation is given below
Speed, N = 1500 rpm. Voltage, V = 230 V. Current, I = 12 A. Fuel volume, fx = 10 cc. Brake power, BP = 4.4 kW.
BP ¼
VI
gg 1000
kW
BP ¼ f ðV; IÞ oBP I 16 ¼ ¼ 0:0188 ¼ ð0:85 1000Þ oV ð0:85 1000Þ oBP V 230 ¼ ¼ 0:2705 ¼ ð0:85 1000Þ ð0:85 1000Þ oI 2sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi3 2 2 oBP oBP DBP ¼ 4 DV þ DI 5 oV oI qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ ð0:0188 10Þ2 þ ð0:2705 0:16Þ2 ¼ 0:1929 kW
Fig. 7 shows the variation of brake thermal efficiency with respect to load. It is observed that the brake thermal efficiency of hydrogen with DEE at 75% load is 29.3% compared to diesel of 21.6%. Whereas in the case of dual fuel mode it is 26.23%. The increase in brake thermal efficiency in the case of hydrogen-DEE operation is due to higher inlet charge cooling that reduced the temperature by about 12–15 °C due to the presence of DEE as a result of its higher latent heat of vapourisation. As the inlet charge cools, the inlet charge (both hydrogen and air) density increases, which in turn results in better combustion, hence an improvement in brake thermal efficiency is noticed. The increase in brake thermal efficiency for hydrogen operation is due to uniformity in mixing hydrogen with air [18]. Fig. 8 shows the variation of specific energy consumption with load. The specific energy consumption of hydrogen-diesel dual fuel is reduced by 24% for hydrogen diesel dual fuel operation at 25% load compared to diesel. The lower specific energy consumption for hydrogen-diesel dual fuel is due to better mixing of hydrogen with air resulting in complete combustion of fuel. With DEE as ignition source for hydrogen the specific energy consumption is 60% lower compared to that of base diesel. The reduction in SEC for hydrogen-DEE dual fuel operation compared to that of hydrogen-diesel dual fuel is due to increased charge density because of the presence of DEE, which reduces the intake temperature by about 15 °C. 7. Combustion characteristics
ð2Þ
The cylinder pressure variation is given in Fig. 9. The maximum firing pressure obtained in hydrogen diesel dual fuel mode is 2% higher than that obtained with diesel. The peak pressure rise corresponds to the large amount of fuel burnt in pre mixed combustion stage and also earlier start of combustion compared to diesel fuel. The peak pressure in the case of hydrogen with DEE reduced by 15% than that of the base diesel. The reduction in peak pressure is due to the use of DEE, which ignites earlier creating a hotter environment inside the combustion chamber thereby reducing the delay period. Fig. 10 shows the pressure crank angle diagram for hydrogendiesel, hydrogen-DEE dual fuel operation and base diesel at 75%
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Hydrogen tank (150 bar) Pressure regulator
Hydrogen (4-5 bar) Filter
Mass flow controller (l/min or kg/h)
Flame trap (Visible indicator for hydrogen flow)
Flame arrestor (Suppress fire hazard)
IR detector 1
ECU (Controlling injection timings) for hydrogen
Battery
ECU (Controlling injection timings) for DEE
Two way valve
Atmosphere
Hydrogen injector
Intake manifold
Engine
DEE injector
DEE pressure regulator IR detector 2
DEE fuel pump
DEE tank
Fig. 6. Work flow diagram for hydrogen and DEE.
Table 3 Hydrogen injector specifications Make Supply voltage Peak current Holding current Flow capacity Working pressure
Quantum technologies 8–16 V 4A 1A 0.8 g/s @ 483–552 kPa 103–552 kPa
load. It is observed that hydrogen diesel dual fuel mode gives a higher peak pressure compared to base diesel fuel. The peak pressure occurs 5° CA earlier than that of diesel. This might be due to the fact that hydrogen combustion is instantaneous compared to diesel combustion. Hydrogen with DEE as ignition source results in a lower cylinder pressure than the base diesel fueling with peak pressure advance of 7° CA than diesel. This may be attributed to charge cooling due to DEE.
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90 80
30
Pressure, bar
Brake thermal efficiency,%
35
25 20 15
Diesel
10
H2 (7.5 lpm) + Diesel H2 + DEE
5
50 40 30
10 0
25
50
75
0 250
100
Load,%
30 25 20 15 Diesel H2 (7.5 lpm) + Diesel H2 + DEE
5 0 0
25
50
310
340
370
400
430
Fig. 10. Variation of cylinder pressure with crank angle at 75% load condition.
35
10
280
Crank angle, deg.
Fig. 7. Variation of brake thermal efficiency with load.
specific energy consumption, MJ/kWh
60
H2 (7.5 lpm) + Diesel H2 + DEE
20
0
75
100
Load,% Fig. 8. Variation of specific energy consumption with load.
Peak pressure, bar
70
Diesel
Fig. 12 shows the rate of pressure rise at 75% load. The rate of pressure rise is higher by about 80% in the case of hydrogen with diesel compared to diesel fuel. The hydrogen with DEE mode results in 11% decrease in the rate of pressure rise than the base diesel fuel. The reduction in the rate of pressure is due to DEE that cools the intake charge, which results in a reduction in combustion chamber pressure. Fig. 13 shows the cumulative heat release at 75% load condition for hydrogen with diesel and DEE mode. The hydrogen diesel dual fuel mode gives similar cumulative heat release pattern as that of diesel. This might be in dual fuel mode while using hydrogen and DEE which undergo instantaneous combustion resulting in rapid combustion of primary fuel followed by lower diffusion period compared to progressive combustion of diesel [20]. Hydrogen with DEE as ignition source results in a lower cumulative heat release than the base diesel fuel. This might be due to DEE that cools the intake charge lowering the temperature inside the engine cylinder.
85
8. Emission characteristics
80
Fig. 14 shows the variation of NOx emission. With hydrogendiesel dual fuel operation NOx is 21.9 g/kW h compared to 20.65 g/kW h for diesel at 75% load. The higher concentration of NOx is due to the peak combustion temperature [21]. With hydrogen-DEE the NOx emission is 0.55 g/kW h. The reduction in NOx emission in the case of DEE operation is due to the lower peak combustion temperature, which is due to inlet charge cooling by around 15 °C [22].
75 70 65
Diesel
60
H2 (7.5 lpm) + Diesel H2 + DEE
55 50 25
50
75
100
Load,% Fig. 9. Variation of peak pressure with load.
Fig. 11 shows the variation of heat release rate (HRR) at 75% load. The HRR was measured with one-degree crank angle accuracy. It is noted that the heat release rate (HRR) is 21% higher for hydrogen operation than the diesel fuel mode. This may be due to the higher flame velocity of hydrogen and also due to instantaneous combustion. The heat released in the premixed combustion zone is higher; this indicates the increased pressure rise in combustion chamber [19]. The hydrogen with DEE mode results in 50% lesser peak heat release rate than the base diesel fuel. This might be due to instantaneous combustion of DEE well before by 20° CA than that of normal combustion of diesel.
120
Heat release rate, J/deg.CA
0
Diesel
100
H2 (7.5 lpm) + Diesel H2 + DEE
80 60 40 20 0 330
350
370
390
410
430
450
Crank angle, deg. Fig. 11. Variation of heat release rate with crank angle at 75% load condition.
3597
7
Diesel
5
H2 (7.5 lpm) + Diesel H2 + DEE
3
1 300 -1
330
360
390
420
450
Oxides of Nitrogen, gm/kWh
Rate of Pressure Rise, bar/deg. CA
N. Saravanan et al. / Fuel 87 (2008) 3591–3599
30 25 20 15
Diesel
10
H2 (7.5 lpm) + Diesel Hydrogen + DEE
5 0 0
25
50
75
100
Load,% -3
Crank angle, deg.
Fig. 14. Variation of oxides of nitrogen with load.
Fig. 12. Variation of rate of pressure rise with crank angle at 75% load condition.
4
Smoke, BSN
300
Cumulative heat release rate, J
Diesel
3.5
250 200
H2 (7.5 lpm) + Diesel H2 + DEE
3 2.5 2 1.5 1
150
0.5 0
330
360
390
420
25
50
75
100
Load,%
H2 (7.5 lpm) + Diesel H2 + DEE
50 0 300
0
Diesel
100
Fig. 15. Variation of smoke with load.
450
2.5
Fig. 13. Variation of cumulative heat release rate with crank angle at 75% load condition.
The variation of smoke with load is shown in Fig. 15. The smoke of 0.7 BSN is observed in hydrogen-DEE operation compared to base diesel fuel of 2.2 BSN and 0.8 BSN for hydrogen-diesel dual fuel at 75% load. The hydrogen on combustion produces mainly water vapor and does not form any particulate matter due to the absence of carbon atom, hence lower smoke level [22]. Fig. 16 shows the variation of hydrocarbon with load. The hydrocarbon increases for hydrogen-DEE operation compared to that of hydrogen-diesel dual fuel operation and base diesel fuel mode. At 25% load hydrocarbon emissions are maximum, it is 2.01 g/kW h in hydrogen-DEE operation compared to both diesel hydrogen-diesel dual fuel of 0.3 g/kW h. While using DEE the cylinder charge temperature is less, which leads to a lower combustion temperature, hence an increase in HC emission. At 75% load the HC emission is found to be 0.322 g/kW h in hydrogen DEE mode compared to diesel of 0.12 g/kW h, whereas in hydrogen-diesel mode it is 0.14 g/kW h. The increase in HC emission is due to the non-availability of oxygen during diffusion combustion period, since hydrogen and DEE undergoes instantaneous combustion as soon as the ignition starts [23]. The variation of carbon monoxide emissions with load is shown in Fig. 17. At 25% load condition CO emission is 1.07 g/kW h in hydrogen with DEE operation, whereas in the hydrogen diesel dual
Hydrocarbon, gm/kWh
Crank angle, deg.
Diesel
2
H2 (7.5 lpm) + Diesel Hdrogen a DEE
1.5 1 0.5 0 0
25
50
75
100
Load, % Fig. 16. Variation of hydrocarbon with load.
fuel mode it is 0.43 g/kW h compared to diesel of 0.64 g/kW h. The higher CO emission during hydrogen-DEE operation is due to the lower combustion temperature. At 75% load the carbon monoxide emission is 0.15 g/kW h in hydrogen-DEE operation and hydrogen diesel dual fuel mode while that of diesel is 0.316 g/kW h. The variation of carbon dioxide emissions with load is shown in Fig. 18. At 25% load the CO2 emissions are 0.47 g/kW h in hydrogen DEE operation. The hydrogen diesel dual fuel mode gives 0.84 g/ kW h compared to diesel of 1.29 g/kW h. At 75% load the carbon dioxide emission is 0.33 g/kW h with hydrogen DEE, whereas in the hydrogen diesel dual fuel mode it is 0.64 g/kW h compared
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Appendix
Carbon Monoxide, gm/kWh
1.2 Diesel
1
S. No.
H2 (7.5 lpm) + Diesel Hydrogen + DEE
0.8 0.6 0.4 0.2 0 0
25
50
75
100
Load,% Fig. 17. Variation of carbon monoxide with load.
1.4
Carbon di oxide, gm/kWh
Diesel
1.2 1 0.8 0.6 0.4 0.2 0 0
25
50
75
Hydrogen-diesel
Hydrogen-DEE
Brake thermal efficiency 1 28.600 11.90 2 50.000 16.85 3 78.600 21.59 4 100.000 23.38
15.29 21.48 25.66 25.45
17.90 24.30 29.30 –
Specific energy consumption 1 28.600 28.8 2 50.000 20.89 3 78.600 16.25 4 100.000 16.42
23.540 16.760 14.020 14.140
17.13 11.19 8.03 –
Oxides of nitrogen 1 28.600 2 50.000 3 78.600 4 100.000
20.36357 21.90777 20.28236 15.8727
Smoke 1 2 3 4 5
H2 (7.5 lpm) + Diesel Hydrogen + DEE
100
Load, % Fig. 18. Variation of carbon dioxide with load.
to diesel of 0.775 g/kW h. The CO2 emissions are lower compared with the base diesel fuel, because of the absence of carbon in hydrogen [24]. 9. Conclusions Experiments were done on a diesel engine using hydrogen in the dual fuel mode and hydrogen with DEE as ignition source. The optimized conditions were found to be 5° CA before gas exchange top dead center (BGTDC) for injection of hydrogen, 30° CA for hydrogen injection duration in the dual fuel mode and 40° CA after gas exchange top dead center (AGTDC) for DEE. The following conclusions are drawn from the present investigation: 1. Hydrogen in both dual fuel and with DEE operation showed an increase in brake thermal efficiency by about 22% and 35%, respectively compared to diesel. 2. A significant reduction in NOx emissions was obtained with DEE operation hydrogen diesel dual fuel mode as well as baseline diesel. 3. Hydrogen diesel and DEE operation exhibited a significant reduction in smoke emissions compared to base diesel fuel. 4. A severe knocking was noticed during the operation of the engine with hydrogen-DEE operation beyond 75% load due to the instantaneous combustion of hydrogen at high loads.
Load
No load 28.600 50.000 78.600 100.000
Diesel
25.34956 20.65469 17.9191 15.95163
0.024683 0.549102 1.267648 –
0.3 1.1 2 2.2 3.6
0 0 0.2 0.8 2
0 0.2 0.3 0.7 –
Hydrocarbon 1 28.600 2 50.000 3 78.600 4 100.000
0.309616 0.203984 0.124092 0.135343
0.290265 0.192958 0.156001 0.135343
2.012502 0.755291 0.322639 –
Carbon monoxide 1 28.600 2 50.000 3 78.600 4 100.000
0.647513 0.368952 0.316366 0.8806
0.431676 0.245968 0.316366 0.5661
1.079189 0.491936 0.158183 –
Carbon dioxide 1 28.600 2 50.000 3 78.600 4 100.000
1.293633 0.934678 0.775098 0.752154
0.840862 0.68871 0.640642 0.683207
0.474332 0.38125 0.332185 –
Peak pressure 1 No load 2 28.600 3 50.000 4 78.600 5 100.000
57 65 71 78.5 82.2
52.7 65.5 71.3 78.5 82.7
51 57.75 64.8 68 –
References [1] Hsu Bertrand D. Practical diesel engine combustion analysis by Bertrand D. Hsu. Society of Automotive Engineers, Inc.; 2002. [2] Ganesan V. Safety aspects for the use of hydrogen, Summer school of hydrogen energy conducted in IIT Madras, 1984. [3] Garni M. A simple and reliable approach for the direct injection of hydrogen in internal combustion engines at low and medium pressures. Int J Hydrogen energy 1995;20:723–6. [4] Haragopala Rao B, Shrivastava KN, Bhakta HN. Hydrogen for dual fuel engine operation. Int J Hydrogen energy 1983;8:381–4. [5] Heywood JB. Internal combustion engine fundamentals. McGraw-Hill series in mechanical engineering. McGraw-Hill; 1998. p. 508-11. [6] Caton JA. An investigation of cause of backfire and its control due to creviced volumes in hydrogen fueled engine. Trans ASME 2001;23:204–10. [7] Das LM. Near-term introduction of hydrogen engines for automotive and agricultural application. Int J Hydrogen energy 2002;27:479–87.
N. Saravanan et al. / Fuel 87 (2008) 3591–3599 [8] Masood M, Ishrat MM, Reddy AS. Computational combustion and emission analysis of hydrogen-diesel blends with experimental verification. Int J Hydrogen Energy 2007;32:2539–47. [9] Lee JT, Kim YY, Lee CW, Caton JA. An investigation of a cause of backfire and its control due to crevice volumes in a hydrogen fueled engine, vol. 123. ASME; 2001. [10] Lee Jong T, Kim YY, Caton Jerald A. The development of a dual injection hydrogen fueled engine with high power and high efficiency. In: 2002 Fall technical conference of ASME-ICED, 8–11 September, 2002. p. 2-12. [11] Das LM. Hydrogen engine: research and development (R&D) programmes in Indian Institute of Technology (IIT), Delhi. Int J Hydrogen Energy 2002;27:953–65. [12] Hashimoto Kohtaro, Ohta Haruya, Hirasawa Tomoko, Arai Mitsuru, Tamura Masamitsu. Evaluation of ignition quality of LPG with cetane number improver, SAE transactions 2002-01-0870, p. 1462–66. [13] Bailey Brent, Eberhardt James, Goguen Steve, Jimell Erwin [Diethyl ether (DEE) as a renewable diesel fuel]. J Fuels Lubricants 1996;106 [Section 3, SAE 972978, SAE transactions]. [14] Furuhama S, Yamane K, Yamaguchi I. Combustion improvement in hydrogen fueled engine. Int J Hydrogen Energy 1977;2:329–40. [15] Lee SJ, Yi HS, Kim ES. Combustion characteristics of intake port injection type hydrogen fuelled engine. Int J Hydrogen Energy 1995;20:317–22. [16] Michael FJ, Brunt, Harjit Rai. The calculation of heat release energy from engine cylinder pressure data. J Fuels Lubricants 1998;107 [Section 4, SAE 981052, SAE transactions].
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[17] Naber JD, Siebers DL. Hydrogen combustion under diesel engine conditions. Int J Hydrogen Energy 1998;23(5):363–71. [18] Stephen A, Ciatti Thomas Wallner, Hendry NG, William FO, Stockhausen, Brad Boyer. Study of combustion analysis of hydrogen internal combustion engine with external mixture formation, ASME internal combustion engine division, ICES 2006-1398, spring technical conference, May 8–10, Germany, 2006. [19] Lee Jong T, Kim YY. The development of a dual injection hydrogen fueled engine with high power and high efficiency. In: 2002 Fall technical conference of ASME-ICED, 8–11 September, 2002. [20] Barreto L, Makihira A, Riahi K. The hydrogen economy in the 21st century: a sustainable development scenario. Int J Hydrogen Energy 2003;28:267–84. [21] Frassoldati A, Faravelli T, Ranzi E. A wide range modeling study of NOx formation and nitrogen chemistry in hydrogen combustion. Int J Hydrogen Energy 2006;31:2310–28. [22] Shudo Toshio, Yamada Hiroyuki. Hydrogen as an ignition-controlling agent for HCCI combustion engine by suppressing the low-temperature oxidation. Int J Hydrogen Energy 2007;32:3066–72. [23] Masood M, Ishrat MM. Computer simulation of hydrogen-diesel dual fuel exhaust gas emissions with experimental verification. Int J Fuel 2008;87(7):1372–8. [24] Arcoumanis Constantine, Bae Choongsik, Crookes Roy, Kinoshita Eiji. The potential of di-methyl ether (DME) as an alternative fuel for compressionignition engines: a review. Int J Fuel 2008;87(7):1014–30.
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Combustion analysis on a DI diesel engine with hydrogen in dual fuel mode N. Saravanan *, G. Nagarajan, G. Sanjay, C. Dhanasekaran, K.M. Kalaiselvan Department of Mechanical Engineering, Internal Combustion Engineering Division, College of Engineering, Guindy, Anna University, Chennai 600 025, India
a r t i c l e
i n f o
Article history: Received 25 January 2008 Received in revised form 4 July 2008 Accepted 8 July 2008 Available online 3 August 2008 Keywords: Hydrogen Port injection Diethyl ether Dual fuel Emission
a b s t r a c t Hydrogen is expected to be one of the most important fuels in the near future to meet the stringent emission norms. In this experimental investigation, the combustion analysis was done on a direct injection (DI) diesel engine using hydrogen with diesel and hydrogen with diethyl ether (DEE) as ignition source. The hydrogen was injected through intake port and diethyl ether was injected through intake manifold and diesel was injected directly inside the combustion chamber. Injection timings for hydrogen and DEE were optimized based on the performance, combustion and emission characteristics of the engine. The optimized timing for the injection of hydrogen was 5° CA before gas exchange top dead center (BGTDC) and 40° CA after gas exchange top dead center (AGTDC) for DEE. From the study it was observed that hydrogen with diesel results in increased brake thermal efficiency by 20% and oxides of nitrogen (NOx) showed an increase of 13% compared to diesel. Hydrogen-DEE operation showed a higher brake thermal efficiency of 30%, with a significant reduction in NOx compared to diesel. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The internal combustion engines have already become an indispensable and integral part of our present day life. In recent days the importance of environment and energy are emphasized in various energy schemes [1]. Increase in stringent environment regulations on exhaust emissions and anticipation of the future depletion of world wide petroleum reserves provide strong encouragement for research on alternate fuels [2]. Hydrogen is one of the most promising alternate fuels. It’s clean burning characteristics and better performance drives more interest in hydrogen fuel [3]. Many researchers have used hydrogen as a fuel in spark ignition (SI) engine [4]. A significant reduction in power output was observed while using hydrogen in SI engine In addition pre ignition, backfire and knocking problems were observed at high load. These problems have resulted in using hydrogen in SI engine within a limited operation range [5,6]. However hydrogen cannot be used as a sole fuel in a compression ignition (CI) engine, since the compression temperature is not enough to initiate the combustion due to its higher self-ignition temperature [7]. Hence an ignition source is required while using it in a CI engine. The simplest method of using hydrogen in a CI engine is to run in the dual fuel mode with diesel as the main fuel or Diethyl Ether can be used that can act as an ignition source for hydrogen. In a dual fuel engine the main fuel is either inducted/carburated or injected into the intake air stream with combustion initiated by diesel. The major energy is obtained from diesel while the rest of the energy is supplied by hydrogen. * Corresponding author. Tel.: +91 9881128166. E-mail address: [email protected] (N. Saravanan). 0016-2361/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2008.07.011
The hydrogen operated dual fuel engine has the property to operate with lean mixtures at part load and no load, which results in NOx reduction, with an increase in thermal efficiency thereby reducing the fuel consumption. It was also observed that hydrogen could be substituted for diesel up to 38% on volume basis without loss in thermal efficiency, however with a nominal power loss. Hydrogen used in the dual fuel mode with diesel by Masood et al. [8] showed the highest brake thermal efficiency of 30% at a compression ratio of 24.5. Lee et al. [9] studied the performance of dual injection hydrogen fueled engine by using solenoid in-cylinder injection and external fuel injection technique. An increase in thermal efficiency by about 22% was noted for dual injection at low loads and 5% at high loads compared to direct injection. Lee et al. [10] suggested that in dual injection, the stability and maximum power could be obtained by direct injection of hydrogen. However the maximum efficiency could be obtained by the external mixture formation in hydrogen engine. Das et al. [11] have carried out experiments on continuous carburation, continuous manifold injection, timed manifold injection and low pressure direct cylinder injection. The maximum brake thermal efficiency of 31.32% was obtained at 2200 rpm with 13 Nm torque. Hashimoto et al. [12] have done extensive experimental investigation with DEE and diesel used as ignition source for igniting hydrogen fuel. Table 1 shows the properties of hydrogen in comparison with diesel and DEE. Fig. 1 shows the photograph of hydrogen and DEE flow arrangements. Electronic injectors for hydrogen can have a greater control over the injection timing and injection duration with quicker response to operate under high-speed conditions [13]. The advantage of hydrogen injection over carburated system is problems like
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Nomenclature J/° kg/h kW mm cm3
CI SI ECU DFC IR NRV DSO LPM UBHC NOx CO BTDC CA HHR
Joules per degree kilograms per hour kilowatts millimeter cubic centimeter
Abbreviations PPM parts per million DEE diethyl ether BSN Bosch smoke number TDC top dead center BGTDC before gas exchange top dead center CAD crank angle duration DI direct injection
Table 1 Properties of hydrogen in comparison with diesel and DEE Sl. No. 1 2 3 4 5 6 7 8 9 10 11 12
13 14 15 16 17
Properties
Diesel
Hydrogen
DEE
Formula Auto ignition temperature (K) Minimum ignition energy (mJ) Flammability limits (volume % in air) Stoichiometric air fuel ratio on mass basis Molecular weight (g mol) Limits of flammability (equivalence ratio) Density at 160 C and 1.01 bar (kg/m3) Net heating valve MJ/kg Flame velocity (cm/s) Quenching gap in NTP air (cm) Diffusivity in air (cm2/s Octane number Research Motor Cetane number Boiling point (K) Viscosity at 15.5 °C, centipoise Vapour pressure at 38 °C kPa Specific gravity
CnH1.8nC8–C20 530 – 0.7–5
H2 858 0.02 4–75
C2H5OC2H5 433 – 1.9–36.0
14.5
34.3
11.1
170 –
2.016 0.1–7.1
74 –
833–881
0.0838
713
42.5 30 – –
119.93 265–325 0.064 0.63
33.9 – – –
30 – 40–55 436–672 2.6–4.1 Negligible 0.83
130 – – 20.27 – – 0.091
– – >125 307.4 0.023 110.3 –
backfire and pre ignition can be eliminated with proper injection timing [14]. The photographic view of the hydrogen injector position on the cylinder head is shown in Fig. 2 and the photographic view of the hydrogen and DEE injector position on the intake manifold is shown in Fig. 3. Fig. 4 shows the cross sectional view of the hydrogen injector. The distinguished feature of hydrogen-operated engine is that it does not produce major pollutants such as hydrocarbon (HC), carbonmonoxide (CO), sulphur dioxide (SO2), lead, smoke, particulate matter, ozone and other carcinogenic compounds. This is due to the absence of carbon and sulphur in hydrogen. However hydrogen-operated engines suffer from the drawback of higher NOx emissions that has an adverse effect on the environment. The formation of NOx could be due to the presence of nitrogen in the fuel and air and also the availability of oxygen in the air. In the case of hydrogen it is obvious that NOx is due to the nitrogen present in air [15]. When the combustion temperature is high some portion of nitrogen present in the air reacts with oxygen to form NOx. One of the ways of reducing NOx is to operate the hydrogen engine with lean mixtures. Lean mixture results in lower temperature that would slower the chemical reaction, which weakens the kinetics
compression ignition spark ignition electronic control unit digital mass flow controller infra red non-return valve digital storage oscilloscope liters per minute unburned hydro carbons nitrogen oxides carbon monoxide before top dead center crank angle heat release rate
of NOx formation [16,17]. NOx emissions increase with increase in equivalence ratio and peaks at an equivalence ratio of 0.9. The objective of the present work is to use hydrogen (by injection in the intake port) in the following ways and study the performance, combustion and emission characteristics and compare with baseline diesel: 1. Hydrogen in the dual fuel mode with diesel. 2. Hydrogen with diethyl ether as an ignition source. 2. Experimental setup and procedure The test engine used was a single cylinder water-cooled DI diesel engine, having a rated power of 3.7 kW that runs at a constant speed of 1500 rpm which was modified to work with hydrogen in the dual fuel mode. The specifications of the test engine are given in Table 2. Fig. 5 shows the schematic view of the experimental setup. The flow diagram for hydrogen and DEE is shown in Fig. 6. The fuel injector was controlled by means of an electronic control unit (ECU). An Infrared detector was used to give signals to the ECU for injector opening based on the preset timing and also to control the duration of injection. The injection timing and injection duration can be varied with the help of ECU. Hydrogen flow was taking place based on the preset value. A pressure regulator as well as a digital mass flow controller controlled the flow. Table 3 shows the technical specifications of the hydrogen injector. In the experimental investigation first the injection timing and injection duration for hydrogen were optimized. For this injection timing from 5° CA before ignition top dead center (BITDC) to 25° CA after ignition top dead center (AITDC) in steps of 5° CA was taken with hydrogen injection duration of 30° CA. 60° CA and 90° CA at a constant hydrogen flow rate of 5.5 liters per minute. The next step in the investigation was optimizing the hydrogen flow. For this hydrogen was varied from 1.5 liters per minute to 9 liters per minute insteps of 1.5 liters per minute for the entire load conditions. The optimized conditions for hydrogen based on the performance, emission and combustion characteristics are as follows. Hydrogen injection timing 5° BGTDC. Hydrogen injection duration 30° CA. Hydrogen flow rate 7.5 liters per minute. 3. Instrumentation An electrical dynamometer with 10 kW capacity with a current rating of 43.5 A was used as a loading device. A non-dispersive infra red (NDIR) type exhaust gas analyzer (Qrotech make) was used
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Fig. 3. Photographic view of the hydrogen and DEE injector position on the intake manifold.
Fig. 1. Photographic view of the hydrogen and DEE flow arrangement.
Fig. 4. Cross sectional view of the hydrogen injector.
Fig. 2. Photographic view of the hydrogen injector position on the cylinder head.
for the measurement of HC, CO, NO and CO2 emissions. Technovision analyzer was used for the measurement of NO2 emission. NOx emission was determined by adding NO and NO2 emissions. Bosch type smoke meter was used to measure smoke intensity. The exhaust gases were filtered and dehumidified by the exhaust gas analyzer before measurement. The gas analyzer was calibrated by passing a known amount of span gases and readings were taken with variation in span gas concentration. If the deviations are outside the accuracy limits the analyzer was calibrated by adjusting the knob for the specific gases. The cylinder pressure was measured using a piezoelectric pressure transducer which has a pressure range of 250 bar and a charge amplifier and the pressure data were given as input to the oscilloscope for further analysis. A Kistler make crank angle encoder with an accuracy of 1° was used for crank angle measurement. After 30 min of engine running on stabilized condition the pressure data were collected. The pressure data’s were collected for 1000 cycles by using Yokogawa data acquisition system. The mass flow of hydrogen was measured
using a digital mass flow controller, which controlled and measured the flow in liters per minute. The engine was operated at a constant speed of 1500 rpm at all loads with torques corresponding to full load percentages. 4. Error analysis and estimation of uncertainity All measurements of physical quantities are subject to uncertainties. Uncertainty analysis is needed to prove the accuracy of the experiments. In order to have reasonable limits of uncertainty for a computed value an expression was derived as follows:
"
DR ¼
oR Dx1 ox1
2
þ
oR Dx2 ox2
2
þ þ
oR Dxn oxn
2 #1=2 ð1Þ
Using Eq. (1) the uncertainty in the computed values such as brake power, brake thermal efficiency and fuel flow measurements were estimated. The measured values such as speed, fuel time, voltage and current were estimated from their respective uncertainties based on the Gaussian distribution. The uncertainties in the measured parameters, voltage (DV) and current (DI), method, were ±10 V and ±0.16 A, respectively. For fuel time (Dtr) and fuel
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Table 2 Engine specifications Make and model General details Number of cylinders Bore Stroke Rated speed Swept volume Clearance volume Compression ratio Rated output Injection pressure Fuel injection timing Type of combustion Lubricating oil Connecting rod length
Kirloskar, AV1 make Four stroke, compression ignition, constant speed, vertical, water-cooled, direct injection. One 80 mm 110 mm 1500 rpm 553 cc 36.87 cc 16.5:1 3.7 kW at 1500 rpm 205 bar 23° BTDC Hemispherical open combustion chamber SAE 20 W40 235 mm
Therefore, the uncertainty in the brake power from Eq. (2) is ±0.1929 kW and the uncertainty limits in the calculation of B.P are 4.4 ± 0.1929 kW. The percentage of uncertainty for the measurement of speed, mass flow rate, NOx, hydrocarbon, smoke and pressure is given below: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii)
Speed: 1.5. Mass flow rate of air: 1.9. Mass flow rate of diesel: 2.1. Mass flow of hydrogen: 1.8. NOx: 2.7. Hydrocarbon: 3.2. Smoke: 2.0. Pressure: 3.2.
5. Results and discussion Experiments were carriedout with hydrogen and diesel in dual fuel operation and with DEE. The engine was not able run beyond 75% load in hydrogen DEE mode due to severe knocking. This is attributed to the instantaneous combustion of both hydrogen and DEE. The numerical values of the results are given in Appendix. 6. Performance characteristics
1. Hydrogen cylinder 2. Pressure regulator 3. Hydrogen tank 4. Filter 5. Digital mass flow controller 6. PC to control DFC 7. Flame trap 8. Flame arrester 9. Hydrogen injector
10. IR sensor for hydrogen 11. Electronic control unit for H2 12. Engine 13. Dynamometer 14. Diesel tank 15. DEE fuel pump 16. DEE Electronic control unit 17. DEE Injector 18. IR sensor for DEE
Fig. 5. Schematic view of the experimental setup.
volume (Dt), the uncertainties were taken as ±0.2 s and ±0.1 s, respectively. A sample calculation is given below
Speed, N = 1500 rpm. Voltage, V = 230 V. Current, I = 12 A. Fuel volume, fx = 10 cc. Brake power, BP = 4.4 kW.
BP ¼
VI
gg 1000
kW
BP ¼ f ðV; IÞ oBP I 16 ¼ ¼ 0:0188 ¼ ð0:85 1000Þ oV ð0:85 1000Þ oBP V 230 ¼ ¼ 0:2705 ¼ ð0:85 1000Þ ð0:85 1000Þ oI 2sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi3 2 2 oBP oBP DBP ¼ 4 DV þ DI 5 oV oI qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi ¼ ð0:0188 10Þ2 þ ð0:2705 0:16Þ2 ¼ 0:1929 kW
Fig. 7 shows the variation of brake thermal efficiency with respect to load. It is observed that the brake thermal efficiency of hydrogen with DEE at 75% load is 29.3% compared to diesel of 21.6%. Whereas in the case of dual fuel mode it is 26.23%. The increase in brake thermal efficiency in the case of hydrogen-DEE operation is due to higher inlet charge cooling that reduced the temperature by about 12–15 °C due to the presence of DEE as a result of its higher latent heat of vapourisation. As the inlet charge cools, the inlet charge (both hydrogen and air) density increases, which in turn results in better combustion, hence an improvement in brake thermal efficiency is noticed. The increase in brake thermal efficiency for hydrogen operation is due to uniformity in mixing hydrogen with air [18]. Fig. 8 shows the variation of specific energy consumption with load. The specific energy consumption of hydrogen-diesel dual fuel is reduced by 24% for hydrogen diesel dual fuel operation at 25% load compared to diesel. The lower specific energy consumption for hydrogen-diesel dual fuel is due to better mixing of hydrogen with air resulting in complete combustion of fuel. With DEE as ignition source for hydrogen the specific energy consumption is 60% lower compared to that of base diesel. The reduction in SEC for hydrogen-DEE dual fuel operation compared to that of hydrogen-diesel dual fuel is due to increased charge density because of the presence of DEE, which reduces the intake temperature by about 15 °C. 7. Combustion characteristics
ð2Þ
The cylinder pressure variation is given in Fig. 9. The maximum firing pressure obtained in hydrogen diesel dual fuel mode is 2% higher than that obtained with diesel. The peak pressure rise corresponds to the large amount of fuel burnt in pre mixed combustion stage and also earlier start of combustion compared to diesel fuel. The peak pressure in the case of hydrogen with DEE reduced by 15% than that of the base diesel. The reduction in peak pressure is due to the use of DEE, which ignites earlier creating a hotter environment inside the combustion chamber thereby reducing the delay period. Fig. 10 shows the pressure crank angle diagram for hydrogendiesel, hydrogen-DEE dual fuel operation and base diesel at 75%
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Hydrogen tank (150 bar) Pressure regulator
Hydrogen (4-5 bar) Filter
Mass flow controller (l/min or kg/h)
Flame trap (Visible indicator for hydrogen flow)
Flame arrestor (Suppress fire hazard)
IR detector 1
ECU (Controlling injection timings) for hydrogen
Battery
ECU (Controlling injection timings) for DEE
Two way valve
Atmosphere
Hydrogen injector
Intake manifold
Engine
DEE injector
DEE pressure regulator IR detector 2
DEE fuel pump
DEE tank
Fig. 6. Work flow diagram for hydrogen and DEE.
Table 3 Hydrogen injector specifications Make Supply voltage Peak current Holding current Flow capacity Working pressure
Quantum technologies 8–16 V 4A 1A 0.8 g/s @ 483–552 kPa 103–552 kPa
load. It is observed that hydrogen diesel dual fuel mode gives a higher peak pressure compared to base diesel fuel. The peak pressure occurs 5° CA earlier than that of diesel. This might be due to the fact that hydrogen combustion is instantaneous compared to diesel combustion. Hydrogen with DEE as ignition source results in a lower cylinder pressure than the base diesel fueling with peak pressure advance of 7° CA than diesel. This may be attributed to charge cooling due to DEE.
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90 80
30
Pressure, bar
Brake thermal efficiency,%
35
25 20 15
Diesel
10
H2 (7.5 lpm) + Diesel H2 + DEE
5
50 40 30
10 0
25
50
75
0 250
100
Load,%
30 25 20 15 Diesel H2 (7.5 lpm) + Diesel H2 + DEE
5 0 0
25
50
310
340
370
400
430
Fig. 10. Variation of cylinder pressure with crank angle at 75% load condition.
35
10
280
Crank angle, deg.
Fig. 7. Variation of brake thermal efficiency with load.
specific energy consumption, MJ/kWh
60
H2 (7.5 lpm) + Diesel H2 + DEE
20
0
75
100
Load,% Fig. 8. Variation of specific energy consumption with load.
Peak pressure, bar
70
Diesel
Fig. 12 shows the rate of pressure rise at 75% load. The rate of pressure rise is higher by about 80% in the case of hydrogen with diesel compared to diesel fuel. The hydrogen with DEE mode results in 11% decrease in the rate of pressure rise than the base diesel fuel. The reduction in the rate of pressure is due to DEE that cools the intake charge, which results in a reduction in combustion chamber pressure. Fig. 13 shows the cumulative heat release at 75% load condition for hydrogen with diesel and DEE mode. The hydrogen diesel dual fuel mode gives similar cumulative heat release pattern as that of diesel. This might be in dual fuel mode while using hydrogen and DEE which undergo instantaneous combustion resulting in rapid combustion of primary fuel followed by lower diffusion period compared to progressive combustion of diesel [20]. Hydrogen with DEE as ignition source results in a lower cumulative heat release than the base diesel fuel. This might be due to DEE that cools the intake charge lowering the temperature inside the engine cylinder.
85
8. Emission characteristics
80
Fig. 14 shows the variation of NOx emission. With hydrogendiesel dual fuel operation NOx is 21.9 g/kW h compared to 20.65 g/kW h for diesel at 75% load. The higher concentration of NOx is due to the peak combustion temperature [21]. With hydrogen-DEE the NOx emission is 0.55 g/kW h. The reduction in NOx emission in the case of DEE operation is due to the lower peak combustion temperature, which is due to inlet charge cooling by around 15 °C [22].
75 70 65
Diesel
60
H2 (7.5 lpm) + Diesel H2 + DEE
55 50 25
50
75
100
Load,% Fig. 9. Variation of peak pressure with load.
Fig. 11 shows the variation of heat release rate (HRR) at 75% load. The HRR was measured with one-degree crank angle accuracy. It is noted that the heat release rate (HRR) is 21% higher for hydrogen operation than the diesel fuel mode. This may be due to the higher flame velocity of hydrogen and also due to instantaneous combustion. The heat released in the premixed combustion zone is higher; this indicates the increased pressure rise in combustion chamber [19]. The hydrogen with DEE mode results in 50% lesser peak heat release rate than the base diesel fuel. This might be due to instantaneous combustion of DEE well before by 20° CA than that of normal combustion of diesel.
120
Heat release rate, J/deg.CA
0
Diesel
100
H2 (7.5 lpm) + Diesel H2 + DEE
80 60 40 20 0 330
350
370
390
410
430
450
Crank angle, deg. Fig. 11. Variation of heat release rate with crank angle at 75% load condition.
3597
7
Diesel
5
H2 (7.5 lpm) + Diesel H2 + DEE
3
1 300 -1
330
360
390
420
450
Oxides of Nitrogen, gm/kWh
Rate of Pressure Rise, bar/deg. CA
N. Saravanan et al. / Fuel 87 (2008) 3591–3599
30 25 20 15
Diesel
10
H2 (7.5 lpm) + Diesel Hydrogen + DEE
5 0 0
25
50
75
100
Load,% -3
Crank angle, deg.
Fig. 14. Variation of oxides of nitrogen with load.
Fig. 12. Variation of rate of pressure rise with crank angle at 75% load condition.
4
Smoke, BSN
300
Cumulative heat release rate, J
Diesel
3.5
250 200
H2 (7.5 lpm) + Diesel H2 + DEE
3 2.5 2 1.5 1
150
0.5 0
330
360
390
420
25
50
75
100
Load,%
H2 (7.5 lpm) + Diesel H2 + DEE
50 0 300
0
Diesel
100
Fig. 15. Variation of smoke with load.
450
2.5
Fig. 13. Variation of cumulative heat release rate with crank angle at 75% load condition.
The variation of smoke with load is shown in Fig. 15. The smoke of 0.7 BSN is observed in hydrogen-DEE operation compared to base diesel fuel of 2.2 BSN and 0.8 BSN for hydrogen-diesel dual fuel at 75% load. The hydrogen on combustion produces mainly water vapor and does not form any particulate matter due to the absence of carbon atom, hence lower smoke level [22]. Fig. 16 shows the variation of hydrocarbon with load. The hydrocarbon increases for hydrogen-DEE operation compared to that of hydrogen-diesel dual fuel operation and base diesel fuel mode. At 25% load hydrocarbon emissions are maximum, it is 2.01 g/kW h in hydrogen-DEE operation compared to both diesel hydrogen-diesel dual fuel of 0.3 g/kW h. While using DEE the cylinder charge temperature is less, which leads to a lower combustion temperature, hence an increase in HC emission. At 75% load the HC emission is found to be 0.322 g/kW h in hydrogen DEE mode compared to diesel of 0.12 g/kW h, whereas in hydrogen-diesel mode it is 0.14 g/kW h. The increase in HC emission is due to the non-availability of oxygen during diffusion combustion period, since hydrogen and DEE undergoes instantaneous combustion as soon as the ignition starts [23]. The variation of carbon monoxide emissions with load is shown in Fig. 17. At 25% load condition CO emission is 1.07 g/kW h in hydrogen with DEE operation, whereas in the hydrogen diesel dual
Hydrocarbon, gm/kWh
Crank angle, deg.
Diesel
2
H2 (7.5 lpm) + Diesel Hdrogen a DEE
1.5 1 0.5 0 0
25
50
75
100
Load, % Fig. 16. Variation of hydrocarbon with load.
fuel mode it is 0.43 g/kW h compared to diesel of 0.64 g/kW h. The higher CO emission during hydrogen-DEE operation is due to the lower combustion temperature. At 75% load the carbon monoxide emission is 0.15 g/kW h in hydrogen-DEE operation and hydrogen diesel dual fuel mode while that of diesel is 0.316 g/kW h. The variation of carbon dioxide emissions with load is shown in Fig. 18. At 25% load the CO2 emissions are 0.47 g/kW h in hydrogen DEE operation. The hydrogen diesel dual fuel mode gives 0.84 g/ kW h compared to diesel of 1.29 g/kW h. At 75% load the carbon dioxide emission is 0.33 g/kW h with hydrogen DEE, whereas in the hydrogen diesel dual fuel mode it is 0.64 g/kW h compared
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Appendix
Carbon Monoxide, gm/kWh
1.2 Diesel
1
S. No.
H2 (7.5 lpm) + Diesel Hydrogen + DEE
0.8 0.6 0.4 0.2 0 0
25
50
75
100
Load,% Fig. 17. Variation of carbon monoxide with load.
1.4
Carbon di oxide, gm/kWh
Diesel
1.2 1 0.8 0.6 0.4 0.2 0 0
25
50
75
Hydrogen-diesel
Hydrogen-DEE
Brake thermal efficiency 1 28.600 11.90 2 50.000 16.85 3 78.600 21.59 4 100.000 23.38
15.29 21.48 25.66 25.45
17.90 24.30 29.30 –
Specific energy consumption 1 28.600 28.8 2 50.000 20.89 3 78.600 16.25 4 100.000 16.42
23.540 16.760 14.020 14.140
17.13 11.19 8.03 –
Oxides of nitrogen 1 28.600 2 50.000 3 78.600 4 100.000
20.36357 21.90777 20.28236 15.8727
Smoke 1 2 3 4 5
H2 (7.5 lpm) + Diesel Hydrogen + DEE
100
Load, % Fig. 18. Variation of carbon dioxide with load.
to diesel of 0.775 g/kW h. The CO2 emissions are lower compared with the base diesel fuel, because of the absence of carbon in hydrogen [24]. 9. Conclusions Experiments were done on a diesel engine using hydrogen in the dual fuel mode and hydrogen with DEE as ignition source. The optimized conditions were found to be 5° CA before gas exchange top dead center (BGTDC) for injection of hydrogen, 30° CA for hydrogen injection duration in the dual fuel mode and 40° CA after gas exchange top dead center (AGTDC) for DEE. The following conclusions are drawn from the present investigation: 1. Hydrogen in both dual fuel and with DEE operation showed an increase in brake thermal efficiency by about 22% and 35%, respectively compared to diesel. 2. A significant reduction in NOx emissions was obtained with DEE operation hydrogen diesel dual fuel mode as well as baseline diesel. 3. Hydrogen diesel and DEE operation exhibited a significant reduction in smoke emissions compared to base diesel fuel. 4. A severe knocking was noticed during the operation of the engine with hydrogen-DEE operation beyond 75% load due to the instantaneous combustion of hydrogen at high loads.
Load
No load 28.600 50.000 78.600 100.000
Diesel
25.34956 20.65469 17.9191 15.95163
0.024683 0.549102 1.267648 –
0.3 1.1 2 2.2 3.6
0 0 0.2 0.8 2
0 0.2 0.3 0.7 –
Hydrocarbon 1 28.600 2 50.000 3 78.600 4 100.000
0.309616 0.203984 0.124092 0.135343
0.290265 0.192958 0.156001 0.135343
2.012502 0.755291 0.322639 –
Carbon monoxide 1 28.600 2 50.000 3 78.600 4 100.000
0.647513 0.368952 0.316366 0.8806
0.431676 0.245968 0.316366 0.5661
1.079189 0.491936 0.158183 –
Carbon dioxide 1 28.600 2 50.000 3 78.600 4 100.000
1.293633 0.934678 0.775098 0.752154
0.840862 0.68871 0.640642 0.683207
0.474332 0.38125 0.332185 –
Peak pressure 1 No load 2 28.600 3 50.000 4 78.600 5 100.000
57 65 71 78.5 82.2
52.7 65.5 71.3 78.5 82.7
51 57.75 64.8 68 –
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