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The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas
Accepted Manuscript Research Paper The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas Sohan Lal, S.K. Mohapatra PII: DOI: Reference:
S1359-4311(16)33511-6 http://dx.doi.org/10.1016/j.applthermaleng.2017.03.038 ATE 10042
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
21 November 2016 8 March 2017 9 March 2017
Please cite this article as: S. Lal, S.K. Mohapatra, The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas, Applied Thermal Engineering (2017), doi: http://dx.doi.org/10.1016/j.applthermaleng.2017.03.038
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The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas Sohan Lal 1, S.K.Mohapatra 2 1,2
Department of Mechanical Engineering, Thapar University, Patiala, Punjab-147004, India Corresponding’s author: [email protected]
Abstract: The emission level produced from agriculture waste during wheat and paddy harvesting season causes an environmental disturbance in many states of India. In the present work, the performance and emission characteristics are studied by using downdraft gasifier and direct injection variable compression diesel engine. Besides emission characteristics, diesel replacement and noise level at different loads and compression ratios were also estimated. It was observed that maximum diesel saving attained was 8.7%, 31.82%, 57.14% and 64.3% at a compression ratio 12, 14, 16 and 18 respectively. An average reduction of 63.62% in HC emission was achieved by increasing the compression ratio from 12 to 18 at 3.2 kW brake power. With dual fuel mode NOx emission was reduced (in the range 35.29– 56.09% for different conditions) as compared to diesel fuel mode. Further, the SOx emission levels were up to 45.45% less in the dual fuel mode. Keywords: Producer gas, Compression ratio, Dual fuel, Emission, Heat release rate, Peak pressure 1.
Introduction
The emission level produced from woody/agriculture wastes are very high in states of India like Punjab and Haryana. The annual biomass generated from agriculture waste in Punjab state alone is 24843 thousand metric ton [1]. Further, it is reported that the annual major crops residue in Punjab state is about 41890 thousand metric ton [2]. These wastes are used to
1
produce the producer gas in a gasifier for running the existing diesel engines for production of electricity mainly in villages for their electric load. In a country like India, various forms of biomass are available like forest waste (twinges, leaves and wood), agriculture waste (rice husk and straw) and industrial waste (wood chips, carpentry shop waste and sawdust). Power generation from biomass gasification may be used for generation of power in remote areas of the country. The producer gas from gasifier may be used to run an internal combustion (IC) engine both compression ignition (CI) and spark ignition (SI). The government of India also runs a national programme on power generation from biomass for the optimum utilization of a variety of agro-based biomass [3]. Researchers have been studying the generation of power from biomass using dual fuel CI engine technology. They have found that use of this technology reduces both nitric oxide (NOx) and soot emission. However, it increases the hydrocarbon (HC) and carbon monoxide(CO) emission. It is reported that this technology results in savings of diesel fuel up to 60–80% [4]–[6]. Many research studies [7]–[10] have reported that for dual fuel mode engine working at low loads, the poor utilization of gaseous fuel results in lower thermal efficiency and higher CO emission as compared to normal diesel fuel operation. Diesel replacement up to 72.3% has been achieved by using hydrogen gas as the secondary fuel but higher energy content of hydrogen gas results in higher NOx emission [11], [12]. Some authors [4], [7], [11] have reported on the performance of diesel engine using liquefied petroleum gas (LPG) composition in the dual fuel mode. The authors have determined the optimum compression ratio and NOx emission. Further, some researchers have investigated the effect of taking compressed natural gas (CNG) gas as a secondary fuel in dual fuel mode on the CO, NOx and HC emissions [9], [10], [13]. The emission characteristics have been studied by using CNG/biogas in dual fuel mode to report on NOx and particulate matter (PM) mass 2
emission[14]. The performance (mainly thermal efficiency) and emissions characteristics (i.e. NOx, HC and CO emissions) of a dual fuel engine using a mixture of hydrogen gas and producer gas have been investigated by a few authors [14]–[16]. Further, it is reported that addition of methane with hydrogen gas results in better hydrogen combustion at higher load conditions[17]. Researchers have also used a mixture of CO and H2 gasses as producer gas and have determined the thermal efficiency and emission levels (CO, HC and NOx). The results showed that NOx emission level reduces while CO and HC emission levels increase as compared to diesel mode [15], [18], [19]. Few researchers have studied the performance and emission characteristics (CO, HC and NOx) by using producer gas obtained from downdraft gasifier using wood chips, charcoal, rice husk, babul wood and coir-pitch as feedstock [5], [20]–[23]. In most of the studies reported in the literature, a simulated fuel (viz.
, CO, methane gas
(CH4), CNG and LPG) has been used along with diesel to investigate the performance and emission characteristics of dual fuel engines. However, very limited literature is available where dual fuel engines have utilized biomass waste as secondary fuel to investigate the performance and emission (HC, CO and NOx) characteristics. In these scant studies, researchers have utilized biomass waste such as coir-pitch [20], wood chips along with mustard oil cake [21], charcoal [5], rice husk [22] and babul wood [23] as a gasifier feedstock. To the best authors’ knowledge, investigation on dual fuel mode diesel engines using sawdust along with cotton stock as a gasifier feedstock have not been reported in the existing literature. Performance indicators (viz. thermal efficiency, engine noise etc.) and emission characteristics using this producer gas (comprising of sawdust and cotton stalks) have not been investigated. Further, very limited literature is available on performance studies of dual fuel mode diesel engine used under conditions of variable compression ratio.
3
Also, there is limited reporting on emission characteristics of dual fuel diesel engines with regards to Sulphur dioxide (SOx) levels. In order to overcome these limitations, in the present work, investigation on performance (BSFC) and emission characteristics (CO, HC, NOx and SOx) have been carried out. This research is important in view of the huge availability of biomass/agriculture waste in India and a large amount of biomass gasification based power generation in the country. So, in the present work, the sawdust and cotton stalks were mixed in the volume ratio of 30:70 and were converted to a gaseous fuel (producer gas) using downdraft gasifier coupled with a variable compression diesel engine to determine the performance and emission characteristics in the diesel mode and dual fuel mode. 2. Material and methods 2.1
Experimental Setup
The experimental set-up consisted of gasifier unit, water pump, gas cooling unit, scrubber, gas filter, bag filter, gas control valves, manometer, eddy current dynamometer with measuring unit and diesel engine. A single cylinder water cooled constant speed 4 stroke variable compression ratio diesel engine (VCR) was used in this study. The detailed specifications of the engine are shown in Table 1. An electrically operated dynamometer (eddy current) was directly coupled to the engine using propeller shaft. The temperature, load and pressure were measured by a digital controller. Downdraft gasifier was used for generation of producer gas from biomass (sawdust and cotton stalks). The detailed specifications of gasifier unit are shown in Table 2. The schematic of the experimental setup is shown in Figure 1. The biomass is fed to the gasifier through its top opening. Air from air inlets (see Figure 1) enters into the combustion zone and generates the producer gas leaves near the bottom of the gasifier having a temperature of about 500 .This hot producer gas is allowed to pass through 4
a gas cooling unit so that the temperature of producer gas can be brought down to ambient temperature. The producer gas is now passed through a scrubber in which a water spray helps in further cooling of the producer gas and it also removes water soluble gases like hydrogen sulfide (H2S) and sulphur dioxide (SO2) from the producer gas. The scrubber also removes any excess soot particles, tar etc. from the producer gas by condensing these impurities. Further, the producer gas was passed through a gas filter and bag filter for further cleaning. The cleaned producer gas coming out of the bag filter has a temperature in the range of 30– 50 . This gas is now safe to be used in IC engine without causing any problems. Biomass input (sawdust and cotton stalks)
Downdraft gasifier Air inlet
Air inlet
Hopper
Digital load, speed, temperature and pressure measurement unit
5
Air inlet
9 6 Gas inlet Gasifier unit
3
Water In
1 Gas cooling unit Water pump
1. 2. 3. 4. 5.
Exhaust gas
Manometer
4
10 Scrubber for gas cleaning
Water out
2
Gas pipe
7
Gas filter
8 Engine
Dynamometer
Combustion chamber Ash box Gas cooling unit Bag filter Flare
6. 7. 8. 9. 10.
Valve Eddy current dynamometer VCR engine Air box Exhaust gas analyzer
Figure 1: Schematic of the experimental setup.
Table 1: Specifications of measuring devices Item Dynamometer
Description Eddy current, water cooled with loading unit
Fuel tank
Capacity 15 l with glass fuel metering column
Calorimeter
Pipe in pipe
Piezo sensor
Range 5000 PSI
Crank angle sensor
Resolution 1 Deg, speed 5500 RPM with TDC pulse
Data acquisition device
NI-6210, 16 bit
Piezo powering unit
Make Cuadra, Model AX-409
Temperature sensor
RTD and Thermocouple Type K
5
Load sensor
Strain gauge, range 0-50 Kg
Fuel flow transmitter
DP transmitter, range 0-500 mm of WC
Air flow transmitter
Pressure transmitter, range (-) 250 mm of WC
Table2: Technical specifications of the gasifier Item
Description
Model
WBG-10 in Ultra clean gas Mode
Type of Gasifier
Downdraft
Gasification temperature
1050ºC-1100ºC
Fuel storage capacity
100kg
Gas flow rate
25Nm3/h
Start-up
Through blower
Biomass Consumption
8 to 9 kg/h
Gasification efficiency
66.14%
Table 3: Composition of the producer gas Item
Composition (%)
Composition (average) (%)
CO
16.1–20.1
18.1
CO2
12–16
14
N2
62.7–50.5
56.6
H2
7.1–9.3
8.2
CH4
2.1–4.1
3.1
Calorific Value
--
4.5MJ/Nm3
Table 4: Specifications of the five gas analyzer Parameter
Range
Resolution
Accuracy
O2
0 to 21%
0.1%
±2% of reading
CO
0 to 5000 ppm
1 ppm
±10 ppm < 400 ppm ±5% of reading>400 ppm
CO2 Derived
0 to 21%
0.1% of reading
±0.3% of reading
HC
0 to 2000 ppm
0.01%
±10% of reading
NOx
0 to 5000 ppm
1 ppm
±5% of reading
Type CRAL Thermocouple
0 to 600
1
±3% of reading
6
Table 5: Test cases calculations BP
Mode
(kW) 0.8
CR12
CR14
CR16
CR18
Diesel
(Kg/h) 0.6
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
0.8
Dual
0.58
0.22
0.45
0.342
0.25
0.518
0.2
0.544
1.6
Diesel
0.75
-
0.7
-
0.7
-
0.7
-
1.6
Dual
0.7
0.452
0.55
0.586
0.3
0.82
0.25
0.774
2.4
Diesel
0.95
-
0.9
-
0.85
-
0.85
-
2.4
Dual
0.88
0.728
0.65
0.862
0.45
1.014
0.4
1.016
3.2
Diesel
1.15
-
1.1
-
1.1
-
1.1
-
3.2
Dual
1.05
0.902
0.75
1.138
0.6
1.224
0.5
1.228
4
Diesel
1.54
-
1.49
-
1.44
-
1.39
-
4
Dual
1.5
1.22
1.25
1.35
1
1.56
0.85
1.59
*
#
Table 6: Basic properties of diesel used Density (kg/m3) 833.7
Cetane number 52.4
Heating value (MJ/kg) 42.70
Sulfur content (mg/kg) 50
Table 7: Characterization of biomass fuel used Biomass
Ash (%)
C (%)
H (%)
N (%)
O (%)
S (%)
Sawdust
1.2
22.28
5.2
0.47
40.85
0
Calorific value (MJ/kg) 18.50
Cotton stalks
6.68
43.60
5.85
0
43.86
0.01
17.40
2.2
Experimental details
Existing diesel engine was altered to operate in dual fuel mode by using mixture of generated gas and air in the engine cylinder. The experimental investigations were carried out on dual fuel mode and diesel mode at different brake power (0.8, 1.6, 2.4, 3.2 and 4.0 kW) and different compression ratio (12, 14, 16 and 18). Four experiments were performed at each brake power and compression ratio. For each case, the mean value of four different observations has been reported in each figure. Also, error bars have been marked on the figures. The flow rates of air and producer gas were measured by u-tube manometers. The engine performance was done on Apex make engine test rig. The reading was stored by using a data logger (NI-USB-6210) with various sensors (RTD, thermocouple, load cell and piezo 7
sensor) in an excel sheet. In each trial, emission data such as CO, HC, CO2, NOx and SOx were studied by five gas analyzer. In addition of emission parameters, thermal performance such as exhaust gas temperature, peak cylinder pressure, net heat released and diesel consumption was studied. The noise level of the engine during experiments was recorded by using portable digital sound level Meter Model: SC310 (Class 1 sound level meter) and measuring range 23-137dBA (manufactured by M/s CESVA instruments). The detail specification of the exhaust gas analyzer is shown in Table 4. In each figure, the mean values were plotted and deviation from mean values are also shown in the figures.
3. Results and observations 3.1
Combustion process in diesel engine with dual fuel mode
The experimental cylinder pressure vs crank position engine data at different load and different compression ratio for 10 cycle expansion and a compression stroke of the engine working cycle can be used for the progress of combustion. By the first law of thermodynamics, the net heat release rate was found [24] using equation (1)
--------- (1)
Where
is heat release rate. γ is specific heat ratio cp/cv. The range of γ for diesel heat
always is 1.3 to 1.35[24]. The producer gas and diesel combustion process is more complex than diesel fuel combustion. During the compression stroke, the producer gas and air-fuel combination undergo pre-ignition. This pre-ignition reaction affects the ignition of diesel fuel. Due to the ignition delay, there was an improvement in the fuel conversion efficiency, due to shorter combustion duration. The ignition delay was observed higher in dual fuel mode than diesel mode. Sombatwong et al.[5] have reported maximum pressure 55.0 bar in diesel mode and
8
56.5 bar in dual fuel mode at a compression ratio of 18. These results are closer to the present study. From the experiment results ignition delay of the pilot, fuel decreases as compression ratio increases. At higher compression ratio, pressure and temperature in the engine cylinder increases. As load increases, the peak cylinder pressure increases for both modes because the high mass of fuel supplied during this period. From the experiment results, the peak cylinder pressure for diesel mode was found to be 37.74, 40.23, 43.72 and 47.19 bar as compares to 32.26, 39.94, 45.29 and 54.49 bar for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. From the Figure 2 (a, b) due to late combustion of producer gas, peak cylinder pressure was shifted towards expansion stroke. It was also observed that the crank angle corresponding to peak cylinder pressure was 15º, 13º, 12º and 12º after top dead center (ATDC) in diesel mode and 26º, 18º, 16º and 14º ATDC in dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. The net heat release rate was calculated by using cylinder pressure data. At different compression ratio, net heat released rate Vs crank angle is shown in Figure 2 (c, d) for diesel and dual fuel mode. It was observed that the net heat release rate decreases with increasing compression ratio. As engine compression ratio increases, with an increase in cylinder temperature, the heat transfer rate increases during combustion. Net heat release rate was found to be 43.15, 37.16, 35.89 and 32.76 J/deg CA for diesel mode and 60.65, 58.01, 52.96 and 46.93 J/deg CA for dual fuel mode at compression ratio 12, 14. 16 and 18 respectively. The ignition delay was found to be 8, 5, 3 and 1 deg ATDC for diesel mode whereas 20, 12, 9 and 4 deg ATDC for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. Sombatwong et al. [5] have reported maximum heat released rate 35.0 J/deg CA for diesel mode and 40.0 J/deg CA for dual fuel mode at a compression ratio of 18. In the present study,
9
the results are closer in diesel mode but higher in dual fuel mode. The reason may be net heat release rate depends upon the amount of fuel burned in the cylinder.
Figure 2: Cylinder pressure and heat release rate with the diesel mode and dual fuel mode at different compression ratio.
3.1. Diesel fuel saving The use of gaseous fuel with diesel reduced the consumption of diesel fuel. The flow of diesel and producer gas shown in Table 5. It was observed that consumption of gaseous fuel increases with increase in compression ratio. It may happen because of higher temperature in the cylinder at a higher compression ratio which helps in the combustion of gaseous fuel. The maximum diesel saving was observed 8.70%, 31.82%, 57.14% and 64.30% at compression ratio (CR) 12, 14, 16 and 18 respectively. Maximum diesel fuel saving at CR 12 and 14 at brake power of 3.2 kW and for compression ratio 16 and 18 at brake power of 1.6 kW as 10
shown in Figure 3. At higher load conditions, diesel fuel saving is reduced because a richer mixture was required at higher loads. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Sombatwong et al. [5] reported a maximum diesel fuel substitution of 64.21%. Similarly, Banapurmath et al. [6] and Yaliwal et al.[23] reported maximum diesel fuel substitution of 70.1% and 65.0% respectively. For the same conditions, a diesel fuel substitution of 64.30% was obtained in the present work.
Figure 3: Variation of diesel saving with brake power at different compression ratio.
3.2. Brake specific fuel consumption (BSFC) BSFC in diesel mode and dual fuel mode are calculated from calorific value and the fuel consumption of diesel and producer gas. It was observed that BSFC in dual fuel mode was 34.40% to 68.75% higher than diesel mode at 3.2 kW brake power. As a result of the lower efficiency in dual fuel mode. It was also observed that BSFC for the part load is higher than higher load. It can be seen from the graph that minimum BSFC is achieved at 2.4 to 3.2 kW brake power as shown in Figure 4 (a, b). The maximum efficiency can be achieved at this load. It was also found that at 70 to 80% load the BSFC was improved. For compression ratio 11
of 18 and 80% load condition, Sombatwong et al. [5] reported maximum BSFC of 0.282 kg/kWh in diesel mode and 0.40 kg/kWh in dual fuel mode. Shrivastava et al. [21] reported maximum BSFC of 0.30kg/kWh in diesel mode and 0.40 kg/kWh in dual fuel mode. Ramadhas et al. [20] reported maximum BSFC of 0.282 and 0.34 in diesel fuel mode and dual fuel mode respectively. For the same conditions, the BSFC of 0.33 kg/kWh in diesel mode and 0.54 kg/kWh in dual fuel mode was obtained in the present work. In the diesel mode BSFC was closer to the previous study and in dual fuel mode the BSFC was higher than previous study because BSFC in dual fuel mode depends on the percentage of gaseous fuel used and calorific value of the gaseous fuel also.
Figure 4: Brake specific fuel consumption of the engine at different compression ratio.
3.3 Noise emission in dual fuel Engine The noise level of the dual fuel engine and single fuel mode was evaluated at different compression ratios and different load conditions as shown in Figure 5 (a, b). The readings were taken one meter away from the engine at the level of the human ear. The sound level was observed to be in the range 80.9 dB(A) to 89.6 dB(A) for dual fuel mode and 81 dB(A) to 89 dB(A) for diesel mode at 3.2kW brake power. It was seen that the effect of CR on the sound level in dual fuel mode was less than that in diesel mode. As seen above, the noise levels are lying within the permissible limits set by Environment Protection Rules, 1986 [25]. 12
Singh et al. [26] reported maximum sound level 98.5 dB(A) at compression ratio of 17. Whereas in a present work 85.0 dB(A) which was lower than previous study.
Figure 5: Variation of sound level in diesel mode and dual fuel mode at different compression ratio.
3.4 Exhaust emission An emission analysis is investigated at different compression ratio and loads for the engine in diesel mode and dual fuel mode. The experimental study of pollutants such as CO, CO2, NOx, SOx and HC are discussed in this section. The variation of NOx emission of diesel mode and dual fuel mode is shown in figure 6 (a, b). As known formation of NOx is favored by high oxygen concentration and high charge temperature [24], [27]. It was observed as the load and compression ratio increases, NOx emission increases. This happened because of more fuel supplied during higher load condition and at higher compression ratio temperature and pressure in the engine cylinder increased. From emission analysis study the maximum concentration of NOx emission in the exhaust gas in diesel mode was found to be 393 ppm. NOx emission from the engine in dual fuel mode varies between 13 to 80 ppm. It was observed that the NOx emission in diesel mode was 35.29% to 56.09% higher than dual fuel mode at 3.2 kW brake power. The lower NOx emission in dual fuel mode was due to the less intense premixed combustion, lower temperature due to the presence of a high amount of producer gas and lower concentration of 13
oxygen in the cylinder. For a compression ratio of 18, Shrivastava et al. [21] reported maximum NOx concentration of 325 ppm in diesel mode and 180 ppm in dual fuel mode at 80% load condition. Dhole et al. [22] reported maximum NOx concentration of 904 ppm in dual fual mode at 80% load condition. Yaliwal et al. [23] reported the concentration of NOx 110 ppm in dual fuel mode at 80% load condition. The concentration of NOx emission in the present study was 200 ppm in diesel mode and 80 ppm in dual fuel mode. The concentration of NOx in the present study was lower than previous reported literature on similar work under the stated conditions. The reason for this trend was the lower temperature in the combustion chamber which results in lower NOx levels. The concentration of NOx in the present study was within the limits (see Table 8) as stated in the Gazette of India: Extraordinary, 2013, Part II-Section 3(I) [28]. The deviation of the CO emission of diesel mode and dual fuel mode operation is shown in Figure 6 (c, d). As we know the amount of CO formation is a function of unburnt gaseous fuel availability and its temperature, both parameters control the rate of fuel decomposition and oxidation [24], [27]. It is observed that CO emission under dual fuel mode was higher than diesel mode of operation. The CO emission was observed 81% to 84% higher in dual fuel mode than diesel mode at 3.2 kW brake power. It was observed that with an increase in load, CO emission decreases in dual fuel mode. This may have happened because of as the engine load increases more fuel is required and as a result, rich air-fuel mixture enters into the cylinder. Due to richer mixture combustion is complete and produces less amount of CO emission. From the figure, it was clear that CO emission decreases as compression ratio increases. From the experiment lower emission were observed at 2.4 to 3.2 kW brake power in both modes of operation. The reasons of higher CO emission in dual fuel mode are low oxygen present in the air-producer gas mixture which yield incomplete combustion. For compression ratio of 18 and 80% load condition, Sombatwong et al. [5] reported the 14
maximum concentration of CO by 100 ppm in diesel mode and 500 ppm in dual fuel mode. Shrivastava et al. [21] reported the maximum concentration of CO by 10 ppm in diesel mode and 250 ppm in dual fuel mode. Ramadhas et al. [20] reported the maximum concentration of CO 700 ppm in diesel mode and 1300 ppm in dual fuel mode. Yaliwal et al. [23] reported the maximum concentration of CO 250 ppm in dual fuel mode only. The concentration of CO emission in the present study was 300 ppm in diesel mode and 1025 ppm in dual fuel mode. However, the concentration of CO in the present work was lower than Ramadhas et al. [19] and higher than Sombatwong et al. [5] and Shrivastava et al. [21]. The reason behind this may be the engine use in these two studies because the CO concentration was also more in diesel fuel mode than the present diesel mode. The variation of hydrocarbon emission at different brake power in diesel mode and dual fuel mode at different compression ratio is shown in Figure 6 (e, f). As observed the variation of HC in the exhaust gaseous is shows the quality of the combustion process of the engine [24], [27]. It was observed that the hydrocarbon emission in dual fuel mode was 63.41% to 70.04% higher than diesel mode. At higher compression ratio, it decreases in both modes of engine operation. Because at higher compression ratio temperature and pressure at the end of the compression stroke is high. The Higher temperature of combustion shows better combustion of fuel. Hence average reduction of 63.62% in HC emission was achieved by increasing the compression ratio from 12 to 18 at 3.2 kW brake power. For compression ratio of 18 and 80% load condition, Shrivastava et al. [21] reported the maximum concentration of HC 15 ppm and 20 ppm in diesel mode and duel fuel mode respectively. Dhole et al. [22] reported the concentration of HC 2400 ppm in dual fuel mode. Banapurmath et al. [6] reported the concentration of HC 46 ppm in dual fuel mode. The concentration of HC emission in the present study was 480 ppm in diesel mode and 1250 ppm in dual fuel mode. However, the concentration of HC in the present work was higher in both modes of operation 15
of the engine as compared to previous literature. The reason may be lower charge temperature, results in slower combustion and allowing a small amount of fuel to escape from the combustion process. However, the concentration of HC in the present study was within the limits (see Table 8) as stated in the Gazette of India: Extraordinary, 2013, Part II-Section 3(I). The variation of sulfur oxide (SOx) emission at different brake power condition in diesel mode and dual fuel mode respectively under conditions of different compression ratio is shown in Figure 8 (a, b). The SOx emission increases with the engine load. This happened because of more quantity of diesel fuel required at higher engine load. It was observed that the SOx emission level in dual fuel mode was lower than diesel fuel mode at different compression ratio values. The SOx emission in dual fuel mode was 0.09%, 31.18%, 45.45% and 54.54% lower as compared to the diesel fuel mode at 80% (3.2kW) load and compression ratio 12, 14, 16 and 18 respectively. The reason for this trend, was the lower sulfur content in biomass (0.01%) fuel than the diesel fuel (0.05%). For compression ratio of 18 and 80% load condition, Saleh, H.E. [7] reported maximum concentration SOx emission to be 25 ppm and Tan et al. [29] reported the maximum concentration of SOx emission as 4.6 ppm. The concentration of SOx emission in the present study was 5.7 ppm in diesel mode and 2.1 ppm in dual fuel mode. The concentration of SOx emission in the present work was lower than the previous literature. Exhaust gas temperature (EGT) was higher in dual fuel mode as compared to diesel mode as shown in Figure 7(a, b). From the observation, the EGT of diesel mode at full load was found to be 330ºC and 380ºC in dual fuel mode. The high EGT in the dual fuel mode is because of higher energy supplied to the engine. It was also noted that the EGT reduce as compression ratio increases from 12 to 18. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Shrivastava et al. 16
[21] reported maximum exhaust gas temperature 250
in diesel mode and 300
in dual fuel
mode. Sombatwong et al.[5] reported maximum exhaust gas temperature 260
in diesel
mode and 320
in dual fuel mode. Ramadhas et al.[20] reported maximum exhaust gas
temperature 390
in diesel mode and 480
in dual fuel mode.
Carbon dioxide (CO2) emission in dual fuel mode was 6.0% to 33.72% higher than diesel mode at 3.2 kW brake power. It was because of producer gas contain some amount of CO2 supply to the engine cylinder. From the observation as load and compression ratio increases, CO2 emission increase in both mode of operation as shown in Figure 7(c, d). The reason behind this was at higher compression ratio temperature and pressure in the engine cylinder increases, higher temperature shows better combustion of fuel. As a result, CO2 emission increases. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Singh et al. [26] reported maximum CO2 emission 3.63% in diesel mode and 7.76% in dual fuel mode and Sahoo et al. [30] reported maximum CO2 emission 8.0% in diesel mode and 6.2% in dual fuel mode. 4. Uncertainty in measurements Uncertainty is associated with an experimental setup like speed manometer
, temperature
, pressure
of full scale,
, crank angle encoder
, the
uncertainty in brake power and specific fuel consumption were obtained as 1.89% and 1.93% respectively [31], [32]. Table 8: Comparison of emission from the diesel engine at 3.2 kW brake power and compression ratio at 18 with the emission limits. Pollutant
Emission limits* (g/kWh)
Emission (g/kWh) Diesel mode
Dual fuel mode
NOx +HC
2.22
3.29
≤ 7.5
CO
0.69
3.96
≤ 3.5
*Emission limits for diesel engine with capacity up to 19kW [28]
17
Figure 6 : Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio.
18
Figure 7: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio.
Figure 8 : Variation of SOx emission in diesel mode and dual fuel mode at different compression ratio.
19
5. Conclusions According to an experimental analysis conducted to analyze the effect of compression ratio on the performance, combustion and emission parameters of a dual fuel diesel engine coupled with downdraft gasifier. 1. Maximum diesel saving attained was 8.7%, 31.82%, 57.14% and 64.3% at compression ratio 12, 14, 16 and 18 respectively. 2. The maximum average cylinder pressure 37.74, 40.23, 43.72 and 47.19 bar for diesel mode and 32.26, 39.94, 45.29 and 54.49 bar for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. 3. CO emission decreases with increase in compression ratio. Lowest CO emission was observed at 2.4 to 3.2 kW brake power in both modes of operation. In dual fuel mode, CO emission was 81% to 84% higher than diesel mode. 4. HC emission was lower in diesel mode than dual fuel mode. The average reduction of 63.62% in HC emission was achieved as compression ratio increases from 12 to 18 at 3.2 kW brake power. 5. NOx emission was 35.29% to 56.09% lower in dual fuel mode. In dual fuel mode, CO2 emission was 6.0% to 33.72% higher than diesel mode. CO2 emission increases with increase in load in both modes. 6. The SOx emission in dual fuel mode was 54.54% lesser as compared to the diesel fuel mode, under condition of 3,2 kW load and compression ratio 18. 7. The effect of compression ratio on noise emission in dual fuel mode was lower as compared to diesel mode.
20
Nomenclature IC CI SI NOx HC CO LPG CNG H2 CH4 SOx BSFC VCR H2S SO2 l PSI RPM TDC WC mm ppm
CR C H N O S kW CO2 ATDC J/deg CA db(A) EGT
internal combustion compression ignition spark ignition oxides of nitrogen hydrocarbon carbon monoxides liquefied petroleum gas compressed natural gas hydrogen gas methane gas sulfur oxide brake specific fuel consumption variable compression ratio hydrogen sulfide sulfur dioxide litre pound per square inch revolution per minutes top dead centre water column millimeter parts per million mass flow of diesel fuel mass flow of producer gas compression ratio carbon hydrogen nitrogen oxygen sulfur kilowatts carbon dioxide gas after top dead centre joules per degree crank angle decibel exhaust gas temperature ( )
21
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[15] M. M. Roy, E. Tomita, N. Kawahara, Y. Harada, and A. Sakane, “Comparison of performance and emissions of a supercharged dual-fuel engine fueled by hydrogen and hydrogen-containing gaseous fuels,” International Journal of Hydrogen Energy, vol. 36, no. 12, pp. 7339–7352, 2011. [16] A. E. Dhole, R. B. Yarasu, and D. B. Lata, “Effect of hydrogen and producer gas as secondary fuels on combustion parameters of a dual fuel diesel engine,” Applied Thermal Engineering, vol. 108, pp. 764–773, 2016. [17] J. H. Zhou, C. S. Cheung, and C. W. Leung, “Combustion, performance and emissions of a diesel engine with H2, CH4 and H2–CH4 addition,” International Journal of Hydrogen Energy, vol. 39, no. 9, pp. 4611–4621, 2014. [18] M. M. Roy, E. Tomita, N. Kawahara, Y. Harada, and A. Sakane, “Performance and emissions of a supercharged dual-fuel engine fueled by hydrogen-rich coke oven gas,” International Journal of Hydrogen Energy, vol. 34, no. 23, pp. 9628–9638, 2009. [19] S. H. Yoon and C. S. Lee, “Experimental investigation on the combustion and exhaust emission characteristics of biogas-biodiesel dual-fuel combustion in a CI engine,” Fuel Processing Technology, vol. 92, no. 5, pp. 992–1000, 2011. [20] A. S. Ramadhas, S. Jayaraj, and C. Muraleedharan, “Dual fuel mode operation in diesel engines using renewable fuels: Rubber seed oil and coir-pith producer gas,” Renewable Energy, vol. 33, no. 9, pp. 2077–2083, 2008. [21] V. Shrivastava, A. K. Jha, A. K. Wamankar, and S. Murugan, “Performance and emission studies of a CI engine coupled with gasifier running in dual fuel mode,” Procedia Engineering, vol. 51, no. NUiCONE 2012, pp. 600–608, 2013. [22] A. E. Dhole, R. B. Yarasu, D. B. Lata, and A. Priyam, “Effect on performance and emissions of a dual fuel diesel engine using hydrogen and producer gas as secondary fuels,” International Journal of Hydrogen Energy, vol. 39, no. 15, pp. 8087–8097, 2014. [23] V. S. Yaliwal, N. R. Banapurmath, N. M. Gireesh, R. S. Hosmath, T. Donateo, and P. G. Tewari, “Effect of nozzle and combustion chamber geometry on the performance of a diesel engine operated on dual fuel mode using renewable fuels,” Renewable Energy, vol. 93, pp. 483–501, 2016. [24] J. Heywood, “Internal combustion engine Fundamentals,” New York: McGraw Hill Book Co., 1988. [25] Government of India, “Environment protection Act, 1986,” 2011, p. 440. [26] R. N. Singh, S. P. Singh, and B. S. Pathak, “Investigations on operation of CI engine using producer gas and rice bran oil in mixed fuel mode,” Renewable Energy, vol. 32, no. 9, pp. 1565–1580, 2007. [27] S. R., Benson and D. N., Whitehouse, “Internal Combustion Engines,” Oxford Pergamon Press, 1973. [28] Government of India, “Emission limits for new diesel engines for generator set applications,” 2013. [29] P. Q. Tan, Z. Y. Hu, and D. M. Lou, “Regulated and unregulated emissions from a light-duty diesel engine with different sulfur content fuels,” Fuel, vol. 88, no. 6, pp. 23
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24
List of Figure Captions Figure 1: Schematic of the experimental setup. Figure 2: Cylinder pressure and heat release rate with the diesel mode and dual fuel mode at different compression ratio. Figure 3: Variation of diesel saving with brake power at different compression ratio. Figure 4: Brake specific fuel consumption of the engine at different compression ratio. Figure 5: Variation of sound level in diesel mode and dual fuel mode at different compression ratio. Figure 6: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio. Figure 7: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio. Figure 8 : Variation of SOx emission in diesel mode and dual fuel mode at different compression ratio.
List of Table Captions Table 1: Specifications of measuring devices. Table2: Technical specifications of the gasifier. Table 3: Composition of the producer gas.
Table 4: Specifications of the five gas analyzer. Table 5: Test cases calculations. Table 6: Basic properties of diesel fuel used. Table 7: Characterization of biomass fuel used. Table 8: Comparison of emission from the diesel engine at 3.2 kW brake power and compression ratio at 18 with the emission limits.
25
Highlights
As compression ratio increases, ignition delay decreases.
In dual fuel mode peak cylinder pressure at a higher compression ratio higher than diesel mode.
SOx emission reduced by 45.45% at 80% load condition in dual fuel mode.
HC and CO emission levels reduced at 60–80% load conditions, in both modes of operation.
1.2% reduction in noise level achieved in dual fuel mode.
26
S1359-4311(16)33511-6 http://dx.doi.org/10.1016/j.applthermaleng.2017.03.038 ATE 10042
To appear in:
Applied Thermal Engineering
Received Date: Revised Date: Accepted Date:
21 November 2016 8 March 2017 9 March 2017
Please cite this article as: S. Lal, S.K. Mohapatra, The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas, Applied Thermal Engineering (2017), doi: http://dx.doi.org/10.1016/j.applthermaleng.2017.03.038
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The effect of compression ratio on the performance and emission characteristics of a dual fuel diesel engine using biomass derived producer gas Sohan Lal 1, S.K.Mohapatra 2 1,2
Department of Mechanical Engineering, Thapar University, Patiala, Punjab-147004, India Corresponding’s author: [email protected]
Abstract: The emission level produced from agriculture waste during wheat and paddy harvesting season causes an environmental disturbance in many states of India. In the present work, the performance and emission characteristics are studied by using downdraft gasifier and direct injection variable compression diesel engine. Besides emission characteristics, diesel replacement and noise level at different loads and compression ratios were also estimated. It was observed that maximum diesel saving attained was 8.7%, 31.82%, 57.14% and 64.3% at a compression ratio 12, 14, 16 and 18 respectively. An average reduction of 63.62% in HC emission was achieved by increasing the compression ratio from 12 to 18 at 3.2 kW brake power. With dual fuel mode NOx emission was reduced (in the range 35.29– 56.09% for different conditions) as compared to diesel fuel mode. Further, the SOx emission levels were up to 45.45% less in the dual fuel mode. Keywords: Producer gas, Compression ratio, Dual fuel, Emission, Heat release rate, Peak pressure 1.
Introduction
The emission level produced from woody/agriculture wastes are very high in states of India like Punjab and Haryana. The annual biomass generated from agriculture waste in Punjab state alone is 24843 thousand metric ton [1]. Further, it is reported that the annual major crops residue in Punjab state is about 41890 thousand metric ton [2]. These wastes are used to
1
produce the producer gas in a gasifier for running the existing diesel engines for production of electricity mainly in villages for their electric load. In a country like India, various forms of biomass are available like forest waste (twinges, leaves and wood), agriculture waste (rice husk and straw) and industrial waste (wood chips, carpentry shop waste and sawdust). Power generation from biomass gasification may be used for generation of power in remote areas of the country. The producer gas from gasifier may be used to run an internal combustion (IC) engine both compression ignition (CI) and spark ignition (SI). The government of India also runs a national programme on power generation from biomass for the optimum utilization of a variety of agro-based biomass [3]. Researchers have been studying the generation of power from biomass using dual fuel CI engine technology. They have found that use of this technology reduces both nitric oxide (NOx) and soot emission. However, it increases the hydrocarbon (HC) and carbon monoxide(CO) emission. It is reported that this technology results in savings of diesel fuel up to 60–80% [4]–[6]. Many research studies [7]–[10] have reported that for dual fuel mode engine working at low loads, the poor utilization of gaseous fuel results in lower thermal efficiency and higher CO emission as compared to normal diesel fuel operation. Diesel replacement up to 72.3% has been achieved by using hydrogen gas as the secondary fuel but higher energy content of hydrogen gas results in higher NOx emission [11], [12]. Some authors [4], [7], [11] have reported on the performance of diesel engine using liquefied petroleum gas (LPG) composition in the dual fuel mode. The authors have determined the optimum compression ratio and NOx emission. Further, some researchers have investigated the effect of taking compressed natural gas (CNG) gas as a secondary fuel in dual fuel mode on the CO, NOx and HC emissions [9], [10], [13]. The emission characteristics have been studied by using CNG/biogas in dual fuel mode to report on NOx and particulate matter (PM) mass 2
emission[14]. The performance (mainly thermal efficiency) and emissions characteristics (i.e. NOx, HC and CO emissions) of a dual fuel engine using a mixture of hydrogen gas and producer gas have been investigated by a few authors [14]–[16]. Further, it is reported that addition of methane with hydrogen gas results in better hydrogen combustion at higher load conditions[17]. Researchers have also used a mixture of CO and H2 gasses as producer gas and have determined the thermal efficiency and emission levels (CO, HC and NOx). The results showed that NOx emission level reduces while CO and HC emission levels increase as compared to diesel mode [15], [18], [19]. Few researchers have studied the performance and emission characteristics (CO, HC and NOx) by using producer gas obtained from downdraft gasifier using wood chips, charcoal, rice husk, babul wood and coir-pitch as feedstock [5], [20]–[23]. In most of the studies reported in the literature, a simulated fuel (viz.
, CO, methane gas
(CH4), CNG and LPG) has been used along with diesel to investigate the performance and emission characteristics of dual fuel engines. However, very limited literature is available where dual fuel engines have utilized biomass waste as secondary fuel to investigate the performance and emission (HC, CO and NOx) characteristics. In these scant studies, researchers have utilized biomass waste such as coir-pitch [20], wood chips along with mustard oil cake [21], charcoal [5], rice husk [22] and babul wood [23] as a gasifier feedstock. To the best authors’ knowledge, investigation on dual fuel mode diesel engines using sawdust along with cotton stock as a gasifier feedstock have not been reported in the existing literature. Performance indicators (viz. thermal efficiency, engine noise etc.) and emission characteristics using this producer gas (comprising of sawdust and cotton stalks) have not been investigated. Further, very limited literature is available on performance studies of dual fuel mode diesel engine used under conditions of variable compression ratio.
3
Also, there is limited reporting on emission characteristics of dual fuel diesel engines with regards to Sulphur dioxide (SOx) levels. In order to overcome these limitations, in the present work, investigation on performance (BSFC) and emission characteristics (CO, HC, NOx and SOx) have been carried out. This research is important in view of the huge availability of biomass/agriculture waste in India and a large amount of biomass gasification based power generation in the country. So, in the present work, the sawdust and cotton stalks were mixed in the volume ratio of 30:70 and were converted to a gaseous fuel (producer gas) using downdraft gasifier coupled with a variable compression diesel engine to determine the performance and emission characteristics in the diesel mode and dual fuel mode. 2. Material and methods 2.1
Experimental Setup
The experimental set-up consisted of gasifier unit, water pump, gas cooling unit, scrubber, gas filter, bag filter, gas control valves, manometer, eddy current dynamometer with measuring unit and diesel engine. A single cylinder water cooled constant speed 4 stroke variable compression ratio diesel engine (VCR) was used in this study. The detailed specifications of the engine are shown in Table 1. An electrically operated dynamometer (eddy current) was directly coupled to the engine using propeller shaft. The temperature, load and pressure were measured by a digital controller. Downdraft gasifier was used for generation of producer gas from biomass (sawdust and cotton stalks). The detailed specifications of gasifier unit are shown in Table 2. The schematic of the experimental setup is shown in Figure 1. The biomass is fed to the gasifier through its top opening. Air from air inlets (see Figure 1) enters into the combustion zone and generates the producer gas leaves near the bottom of the gasifier having a temperature of about 500 .This hot producer gas is allowed to pass through 4
a gas cooling unit so that the temperature of producer gas can be brought down to ambient temperature. The producer gas is now passed through a scrubber in which a water spray helps in further cooling of the producer gas and it also removes water soluble gases like hydrogen sulfide (H2S) and sulphur dioxide (SO2) from the producer gas. The scrubber also removes any excess soot particles, tar etc. from the producer gas by condensing these impurities. Further, the producer gas was passed through a gas filter and bag filter for further cleaning. The cleaned producer gas coming out of the bag filter has a temperature in the range of 30– 50 . This gas is now safe to be used in IC engine without causing any problems. Biomass input (sawdust and cotton stalks)
Downdraft gasifier Air inlet
Air inlet
Hopper
Digital load, speed, temperature and pressure measurement unit
5
Air inlet
9 6 Gas inlet Gasifier unit
3
Water In
1 Gas cooling unit Water pump
1. 2. 3. 4. 5.
Exhaust gas
Manometer
4
10 Scrubber for gas cleaning
Water out
2
Gas pipe
7
Gas filter
8 Engine
Dynamometer
Combustion chamber Ash box Gas cooling unit Bag filter Flare
6. 7. 8. 9. 10.
Valve Eddy current dynamometer VCR engine Air box Exhaust gas analyzer
Figure 1: Schematic of the experimental setup.
Table 1: Specifications of measuring devices Item Dynamometer
Description Eddy current, water cooled with loading unit
Fuel tank
Capacity 15 l with glass fuel metering column
Calorimeter
Pipe in pipe
Piezo sensor
Range 5000 PSI
Crank angle sensor
Resolution 1 Deg, speed 5500 RPM with TDC pulse
Data acquisition device
NI-6210, 16 bit
Piezo powering unit
Make Cuadra, Model AX-409
Temperature sensor
RTD and Thermocouple Type K
5
Load sensor
Strain gauge, range 0-50 Kg
Fuel flow transmitter
DP transmitter, range 0-500 mm of WC
Air flow transmitter
Pressure transmitter, range (-) 250 mm of WC
Table2: Technical specifications of the gasifier Item
Description
Model
WBG-10 in Ultra clean gas Mode
Type of Gasifier
Downdraft
Gasification temperature
1050ºC-1100ºC
Fuel storage capacity
100kg
Gas flow rate
25Nm3/h
Start-up
Through blower
Biomass Consumption
8 to 9 kg/h
Gasification efficiency
66.14%
Table 3: Composition of the producer gas Item
Composition (%)
Composition (average) (%)
CO
16.1–20.1
18.1
CO2
12–16
14
N2
62.7–50.5
56.6
H2
7.1–9.3
8.2
CH4
2.1–4.1
3.1
Calorific Value
--
4.5MJ/Nm3
Table 4: Specifications of the five gas analyzer Parameter
Range
Resolution
Accuracy
O2
0 to 21%
0.1%
±2% of reading
CO
0 to 5000 ppm
1 ppm
±10 ppm < 400 ppm ±5% of reading>400 ppm
CO2 Derived
0 to 21%
0.1% of reading
±0.3% of reading
HC
0 to 2000 ppm
0.01%
±10% of reading
NOx
0 to 5000 ppm
1 ppm
±5% of reading
Type CRAL Thermocouple
0 to 600
1
±3% of reading
6
Table 5: Test cases calculations BP
Mode
(kW) 0.8
CR12
CR14
CR16
CR18
Diesel
(Kg/h) 0.6
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
(Kg/h) 0.55
(Kg/h) -
0.8
Dual
0.58
0.22
0.45
0.342
0.25
0.518
0.2
0.544
1.6
Diesel
0.75
-
0.7
-
0.7
-
0.7
-
1.6
Dual
0.7
0.452
0.55
0.586
0.3
0.82
0.25
0.774
2.4
Diesel
0.95
-
0.9
-
0.85
-
0.85
-
2.4
Dual
0.88
0.728
0.65
0.862
0.45
1.014
0.4
1.016
3.2
Diesel
1.15
-
1.1
-
1.1
-
1.1
-
3.2
Dual
1.05
0.902
0.75
1.138
0.6
1.224
0.5
1.228
4
Diesel
1.54
-
1.49
-
1.44
-
1.39
-
4
Dual
1.5
1.22
1.25
1.35
1
1.56
0.85
1.59
*
#
Table 6: Basic properties of diesel used Density (kg/m3) 833.7
Cetane number 52.4
Heating value (MJ/kg) 42.70
Sulfur content (mg/kg) 50
Table 7: Characterization of biomass fuel used Biomass
Ash (%)
C (%)
H (%)
N (%)
O (%)
S (%)
Sawdust
1.2
22.28
5.2
0.47
40.85
0
Calorific value (MJ/kg) 18.50
Cotton stalks
6.68
43.60
5.85
0
43.86
0.01
17.40
2.2
Experimental details
Existing diesel engine was altered to operate in dual fuel mode by using mixture of generated gas and air in the engine cylinder. The experimental investigations were carried out on dual fuel mode and diesel mode at different brake power (0.8, 1.6, 2.4, 3.2 and 4.0 kW) and different compression ratio (12, 14, 16 and 18). Four experiments were performed at each brake power and compression ratio. For each case, the mean value of four different observations has been reported in each figure. Also, error bars have been marked on the figures. The flow rates of air and producer gas were measured by u-tube manometers. The engine performance was done on Apex make engine test rig. The reading was stored by using a data logger (NI-USB-6210) with various sensors (RTD, thermocouple, load cell and piezo 7
sensor) in an excel sheet. In each trial, emission data such as CO, HC, CO2, NOx and SOx were studied by five gas analyzer. In addition of emission parameters, thermal performance such as exhaust gas temperature, peak cylinder pressure, net heat released and diesel consumption was studied. The noise level of the engine during experiments was recorded by using portable digital sound level Meter Model: SC310 (Class 1 sound level meter) and measuring range 23-137dBA (manufactured by M/s CESVA instruments). The detail specification of the exhaust gas analyzer is shown in Table 4. In each figure, the mean values were plotted and deviation from mean values are also shown in the figures.
3. Results and observations 3.1
Combustion process in diesel engine with dual fuel mode
The experimental cylinder pressure vs crank position engine data at different load and different compression ratio for 10 cycle expansion and a compression stroke of the engine working cycle can be used for the progress of combustion. By the first law of thermodynamics, the net heat release rate was found [24] using equation (1)
--------- (1)
Where
is heat release rate. γ is specific heat ratio cp/cv. The range of γ for diesel heat
always is 1.3 to 1.35[24]. The producer gas and diesel combustion process is more complex than diesel fuel combustion. During the compression stroke, the producer gas and air-fuel combination undergo pre-ignition. This pre-ignition reaction affects the ignition of diesel fuel. Due to the ignition delay, there was an improvement in the fuel conversion efficiency, due to shorter combustion duration. The ignition delay was observed higher in dual fuel mode than diesel mode. Sombatwong et al.[5] have reported maximum pressure 55.0 bar in diesel mode and
8
56.5 bar in dual fuel mode at a compression ratio of 18. These results are closer to the present study. From the experiment results ignition delay of the pilot, fuel decreases as compression ratio increases. At higher compression ratio, pressure and temperature in the engine cylinder increases. As load increases, the peak cylinder pressure increases for both modes because the high mass of fuel supplied during this period. From the experiment results, the peak cylinder pressure for diesel mode was found to be 37.74, 40.23, 43.72 and 47.19 bar as compares to 32.26, 39.94, 45.29 and 54.49 bar for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. From the Figure 2 (a, b) due to late combustion of producer gas, peak cylinder pressure was shifted towards expansion stroke. It was also observed that the crank angle corresponding to peak cylinder pressure was 15º, 13º, 12º and 12º after top dead center (ATDC) in diesel mode and 26º, 18º, 16º and 14º ATDC in dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. The net heat release rate was calculated by using cylinder pressure data. At different compression ratio, net heat released rate Vs crank angle is shown in Figure 2 (c, d) for diesel and dual fuel mode. It was observed that the net heat release rate decreases with increasing compression ratio. As engine compression ratio increases, with an increase in cylinder temperature, the heat transfer rate increases during combustion. Net heat release rate was found to be 43.15, 37.16, 35.89 and 32.76 J/deg CA for diesel mode and 60.65, 58.01, 52.96 and 46.93 J/deg CA for dual fuel mode at compression ratio 12, 14. 16 and 18 respectively. The ignition delay was found to be 8, 5, 3 and 1 deg ATDC for diesel mode whereas 20, 12, 9 and 4 deg ATDC for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. Sombatwong et al. [5] have reported maximum heat released rate 35.0 J/deg CA for diesel mode and 40.0 J/deg CA for dual fuel mode at a compression ratio of 18. In the present study,
9
the results are closer in diesel mode but higher in dual fuel mode. The reason may be net heat release rate depends upon the amount of fuel burned in the cylinder.
Figure 2: Cylinder pressure and heat release rate with the diesel mode and dual fuel mode at different compression ratio.
3.1. Diesel fuel saving The use of gaseous fuel with diesel reduced the consumption of diesel fuel. The flow of diesel and producer gas shown in Table 5. It was observed that consumption of gaseous fuel increases with increase in compression ratio. It may happen because of higher temperature in the cylinder at a higher compression ratio which helps in the combustion of gaseous fuel. The maximum diesel saving was observed 8.70%, 31.82%, 57.14% and 64.30% at compression ratio (CR) 12, 14, 16 and 18 respectively. Maximum diesel fuel saving at CR 12 and 14 at brake power of 3.2 kW and for compression ratio 16 and 18 at brake power of 1.6 kW as 10
shown in Figure 3. At higher load conditions, diesel fuel saving is reduced because a richer mixture was required at higher loads. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Sombatwong et al. [5] reported a maximum diesel fuel substitution of 64.21%. Similarly, Banapurmath et al. [6] and Yaliwal et al.[23] reported maximum diesel fuel substitution of 70.1% and 65.0% respectively. For the same conditions, a diesel fuel substitution of 64.30% was obtained in the present work.
Figure 3: Variation of diesel saving with brake power at different compression ratio.
3.2. Brake specific fuel consumption (BSFC) BSFC in diesel mode and dual fuel mode are calculated from calorific value and the fuel consumption of diesel and producer gas. It was observed that BSFC in dual fuel mode was 34.40% to 68.75% higher than diesel mode at 3.2 kW brake power. As a result of the lower efficiency in dual fuel mode. It was also observed that BSFC for the part load is higher than higher load. It can be seen from the graph that minimum BSFC is achieved at 2.4 to 3.2 kW brake power as shown in Figure 4 (a, b). The maximum efficiency can be achieved at this load. It was also found that at 70 to 80% load the BSFC was improved. For compression ratio 11
of 18 and 80% load condition, Sombatwong et al. [5] reported maximum BSFC of 0.282 kg/kWh in diesel mode and 0.40 kg/kWh in dual fuel mode. Shrivastava et al. [21] reported maximum BSFC of 0.30kg/kWh in diesel mode and 0.40 kg/kWh in dual fuel mode. Ramadhas et al. [20] reported maximum BSFC of 0.282 and 0.34 in diesel fuel mode and dual fuel mode respectively. For the same conditions, the BSFC of 0.33 kg/kWh in diesel mode and 0.54 kg/kWh in dual fuel mode was obtained in the present work. In the diesel mode BSFC was closer to the previous study and in dual fuel mode the BSFC was higher than previous study because BSFC in dual fuel mode depends on the percentage of gaseous fuel used and calorific value of the gaseous fuel also.
Figure 4: Brake specific fuel consumption of the engine at different compression ratio.
3.3 Noise emission in dual fuel Engine The noise level of the dual fuel engine and single fuel mode was evaluated at different compression ratios and different load conditions as shown in Figure 5 (a, b). The readings were taken one meter away from the engine at the level of the human ear. The sound level was observed to be in the range 80.9 dB(A) to 89.6 dB(A) for dual fuel mode and 81 dB(A) to 89 dB(A) for diesel mode at 3.2kW brake power. It was seen that the effect of CR on the sound level in dual fuel mode was less than that in diesel mode. As seen above, the noise levels are lying within the permissible limits set by Environment Protection Rules, 1986 [25]. 12
Singh et al. [26] reported maximum sound level 98.5 dB(A) at compression ratio of 17. Whereas in a present work 85.0 dB(A) which was lower than previous study.
Figure 5: Variation of sound level in diesel mode and dual fuel mode at different compression ratio.
3.4 Exhaust emission An emission analysis is investigated at different compression ratio and loads for the engine in diesel mode and dual fuel mode. The experimental study of pollutants such as CO, CO2, NOx, SOx and HC are discussed in this section. The variation of NOx emission of diesel mode and dual fuel mode is shown in figure 6 (a, b). As known formation of NOx is favored by high oxygen concentration and high charge temperature [24], [27]. It was observed as the load and compression ratio increases, NOx emission increases. This happened because of more fuel supplied during higher load condition and at higher compression ratio temperature and pressure in the engine cylinder increased. From emission analysis study the maximum concentration of NOx emission in the exhaust gas in diesel mode was found to be 393 ppm. NOx emission from the engine in dual fuel mode varies between 13 to 80 ppm. It was observed that the NOx emission in diesel mode was 35.29% to 56.09% higher than dual fuel mode at 3.2 kW brake power. The lower NOx emission in dual fuel mode was due to the less intense premixed combustion, lower temperature due to the presence of a high amount of producer gas and lower concentration of 13
oxygen in the cylinder. For a compression ratio of 18, Shrivastava et al. [21] reported maximum NOx concentration of 325 ppm in diesel mode and 180 ppm in dual fuel mode at 80% load condition. Dhole et al. [22] reported maximum NOx concentration of 904 ppm in dual fual mode at 80% load condition. Yaliwal et al. [23] reported the concentration of NOx 110 ppm in dual fuel mode at 80% load condition. The concentration of NOx emission in the present study was 200 ppm in diesel mode and 80 ppm in dual fuel mode. The concentration of NOx in the present study was lower than previous reported literature on similar work under the stated conditions. The reason for this trend was the lower temperature in the combustion chamber which results in lower NOx levels. The concentration of NOx in the present study was within the limits (see Table 8) as stated in the Gazette of India: Extraordinary, 2013, Part II-Section 3(I) [28]. The deviation of the CO emission of diesel mode and dual fuel mode operation is shown in Figure 6 (c, d). As we know the amount of CO formation is a function of unburnt gaseous fuel availability and its temperature, both parameters control the rate of fuel decomposition and oxidation [24], [27]. It is observed that CO emission under dual fuel mode was higher than diesel mode of operation. The CO emission was observed 81% to 84% higher in dual fuel mode than diesel mode at 3.2 kW brake power. It was observed that with an increase in load, CO emission decreases in dual fuel mode. This may have happened because of as the engine load increases more fuel is required and as a result, rich air-fuel mixture enters into the cylinder. Due to richer mixture combustion is complete and produces less amount of CO emission. From the figure, it was clear that CO emission decreases as compression ratio increases. From the experiment lower emission were observed at 2.4 to 3.2 kW brake power in both modes of operation. The reasons of higher CO emission in dual fuel mode are low oxygen present in the air-producer gas mixture which yield incomplete combustion. For compression ratio of 18 and 80% load condition, Sombatwong et al. [5] reported the 14
maximum concentration of CO by 100 ppm in diesel mode and 500 ppm in dual fuel mode. Shrivastava et al. [21] reported the maximum concentration of CO by 10 ppm in diesel mode and 250 ppm in dual fuel mode. Ramadhas et al. [20] reported the maximum concentration of CO 700 ppm in diesel mode and 1300 ppm in dual fuel mode. Yaliwal et al. [23] reported the maximum concentration of CO 250 ppm in dual fuel mode only. The concentration of CO emission in the present study was 300 ppm in diesel mode and 1025 ppm in dual fuel mode. However, the concentration of CO in the present work was lower than Ramadhas et al. [19] and higher than Sombatwong et al. [5] and Shrivastava et al. [21]. The reason behind this may be the engine use in these two studies because the CO concentration was also more in diesel fuel mode than the present diesel mode. The variation of hydrocarbon emission at different brake power in diesel mode and dual fuel mode at different compression ratio is shown in Figure 6 (e, f). As observed the variation of HC in the exhaust gaseous is shows the quality of the combustion process of the engine [24], [27]. It was observed that the hydrocarbon emission in dual fuel mode was 63.41% to 70.04% higher than diesel mode. At higher compression ratio, it decreases in both modes of engine operation. Because at higher compression ratio temperature and pressure at the end of the compression stroke is high. The Higher temperature of combustion shows better combustion of fuel. Hence average reduction of 63.62% in HC emission was achieved by increasing the compression ratio from 12 to 18 at 3.2 kW brake power. For compression ratio of 18 and 80% load condition, Shrivastava et al. [21] reported the maximum concentration of HC 15 ppm and 20 ppm in diesel mode and duel fuel mode respectively. Dhole et al. [22] reported the concentration of HC 2400 ppm in dual fuel mode. Banapurmath et al. [6] reported the concentration of HC 46 ppm in dual fuel mode. The concentration of HC emission in the present study was 480 ppm in diesel mode and 1250 ppm in dual fuel mode. However, the concentration of HC in the present work was higher in both modes of operation 15
of the engine as compared to previous literature. The reason may be lower charge temperature, results in slower combustion and allowing a small amount of fuel to escape from the combustion process. However, the concentration of HC in the present study was within the limits (see Table 8) as stated in the Gazette of India: Extraordinary, 2013, Part II-Section 3(I). The variation of sulfur oxide (SOx) emission at different brake power condition in diesel mode and dual fuel mode respectively under conditions of different compression ratio is shown in Figure 8 (a, b). The SOx emission increases with the engine load. This happened because of more quantity of diesel fuel required at higher engine load. It was observed that the SOx emission level in dual fuel mode was lower than diesel fuel mode at different compression ratio values. The SOx emission in dual fuel mode was 0.09%, 31.18%, 45.45% and 54.54% lower as compared to the diesel fuel mode at 80% (3.2kW) load and compression ratio 12, 14, 16 and 18 respectively. The reason for this trend, was the lower sulfur content in biomass (0.01%) fuel than the diesel fuel (0.05%). For compression ratio of 18 and 80% load condition, Saleh, H.E. [7] reported maximum concentration SOx emission to be 25 ppm and Tan et al. [29] reported the maximum concentration of SOx emission as 4.6 ppm. The concentration of SOx emission in the present study was 5.7 ppm in diesel mode and 2.1 ppm in dual fuel mode. The concentration of SOx emission in the present work was lower than the previous literature. Exhaust gas temperature (EGT) was higher in dual fuel mode as compared to diesel mode as shown in Figure 7(a, b). From the observation, the EGT of diesel mode at full load was found to be 330ºC and 380ºC in dual fuel mode. The high EGT in the dual fuel mode is because of higher energy supplied to the engine. It was also noted that the EGT reduce as compression ratio increases from 12 to 18. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Shrivastava et al. 16
[21] reported maximum exhaust gas temperature 250
in diesel mode and 300
in dual fuel
mode. Sombatwong et al.[5] reported maximum exhaust gas temperature 260
in diesel
mode and 320
in dual fuel mode. Ramadhas et al.[20] reported maximum exhaust gas
temperature 390
in diesel mode and 480
in dual fuel mode.
Carbon dioxide (CO2) emission in dual fuel mode was 6.0% to 33.72% higher than diesel mode at 3.2 kW brake power. It was because of producer gas contain some amount of CO2 supply to the engine cylinder. From the observation as load and compression ratio increases, CO2 emission increase in both mode of operation as shown in Figure 7(c, d). The reason behind this was at higher compression ratio temperature and pressure in the engine cylinder increases, higher temperature shows better combustion of fuel. As a result, CO2 emission increases. The results obtained in present work are in closer agreement with the reported literature. For example, for the compression ratio of 18, Singh et al. [26] reported maximum CO2 emission 3.63% in diesel mode and 7.76% in dual fuel mode and Sahoo et al. [30] reported maximum CO2 emission 8.0% in diesel mode and 6.2% in dual fuel mode. 4. Uncertainty in measurements Uncertainty is associated with an experimental setup like speed manometer
, temperature
, pressure
of full scale,
, crank angle encoder
, the
uncertainty in brake power and specific fuel consumption were obtained as 1.89% and 1.93% respectively [31], [32]. Table 8: Comparison of emission from the diesel engine at 3.2 kW brake power and compression ratio at 18 with the emission limits. Pollutant
Emission limits* (g/kWh)
Emission (g/kWh) Diesel mode
Dual fuel mode
NOx +HC
2.22
3.29
≤ 7.5
CO
0.69
3.96
≤ 3.5
*Emission limits for diesel engine with capacity up to 19kW [28]
17
Figure 6 : Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio.
18
Figure 7: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio.
Figure 8 : Variation of SOx emission in diesel mode and dual fuel mode at different compression ratio.
19
5. Conclusions According to an experimental analysis conducted to analyze the effect of compression ratio on the performance, combustion and emission parameters of a dual fuel diesel engine coupled with downdraft gasifier. 1. Maximum diesel saving attained was 8.7%, 31.82%, 57.14% and 64.3% at compression ratio 12, 14, 16 and 18 respectively. 2. The maximum average cylinder pressure 37.74, 40.23, 43.72 and 47.19 bar for diesel mode and 32.26, 39.94, 45.29 and 54.49 bar for dual fuel mode at compression ratio 12, 14, 16 and 18 respectively. 3. CO emission decreases with increase in compression ratio. Lowest CO emission was observed at 2.4 to 3.2 kW brake power in both modes of operation. In dual fuel mode, CO emission was 81% to 84% higher than diesel mode. 4. HC emission was lower in diesel mode than dual fuel mode. The average reduction of 63.62% in HC emission was achieved as compression ratio increases from 12 to 18 at 3.2 kW brake power. 5. NOx emission was 35.29% to 56.09% lower in dual fuel mode. In dual fuel mode, CO2 emission was 6.0% to 33.72% higher than diesel mode. CO2 emission increases with increase in load in both modes. 6. The SOx emission in dual fuel mode was 54.54% lesser as compared to the diesel fuel mode, under condition of 3,2 kW load and compression ratio 18. 7. The effect of compression ratio on noise emission in dual fuel mode was lower as compared to diesel mode.
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Nomenclature IC CI SI NOx HC CO LPG CNG H2 CH4 SOx BSFC VCR H2S SO2 l PSI RPM TDC WC mm ppm
CR C H N O S kW CO2 ATDC J/deg CA db(A) EGT
internal combustion compression ignition spark ignition oxides of nitrogen hydrocarbon carbon monoxides liquefied petroleum gas compressed natural gas hydrogen gas methane gas sulfur oxide brake specific fuel consumption variable compression ratio hydrogen sulfide sulfur dioxide litre pound per square inch revolution per minutes top dead centre water column millimeter parts per million mass flow of diesel fuel mass flow of producer gas compression ratio carbon hydrogen nitrogen oxygen sulfur kilowatts carbon dioxide gas after top dead centre joules per degree crank angle decibel exhaust gas temperature ( )
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List of Figure Captions Figure 1: Schematic of the experimental setup. Figure 2: Cylinder pressure and heat release rate with the diesel mode and dual fuel mode at different compression ratio. Figure 3: Variation of diesel saving with brake power at different compression ratio. Figure 4: Brake specific fuel consumption of the engine at different compression ratio. Figure 5: Variation of sound level in diesel mode and dual fuel mode at different compression ratio. Figure 6: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio. Figure 7: Variation of exhaust emission in diesel mode and dual fuel mode at different compression ratio. Figure 8 : Variation of SOx emission in diesel mode and dual fuel mode at different compression ratio.
List of Table Captions Table 1: Specifications of measuring devices. Table2: Technical specifications of the gasifier. Table 3: Composition of the producer gas.
Table 4: Specifications of the five gas analyzer. Table 5: Test cases calculations. Table 6: Basic properties of diesel fuel used. Table 7: Characterization of biomass fuel used. Table 8: Comparison of emission from the diesel engine at 3.2 kW brake power and compression ratio at 18 with the emission limits.
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Highlights
As compression ratio increases, ignition delay decreases.
In dual fuel mode peak cylinder pressure at a higher compression ratio higher than diesel mode.
SOx emission reduced by 45.45% at 80% load condition in dual fuel mode.
HC and CO emission levels reduced at 60–80% load conditions, in both modes of operation.
1.2% reduction in noise level achieved in dual fuel mode.
26