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Volume-7, Issue-1, January-February 2017

International Journal of Engineering and Management Research

Page Number: 90-99

Comprehensive Review on Performance, Combustion and Emission

Characteristics of Compression Ignition Engine Fuelled with Producer

Gas in Dual Fuel Mode

Praveen A. Harari1, Amit Deokar2, Dr. Bimlesh Kumar3, Santosh Ghorpade4, Somanagouda Biradar5 1,2

Assistant Professor, Department of Mechanical Engineering, Sant Gajanan Maharaj College of Engineering, Mahagaon, Gadahinglaj, Maharashtra, INDIA

3_{Principal, Sant Gajanan Maharaj College of Engineering, Mahagaon, Gadahinglaj, Maharashtra, INDIA} 4

Assistant Professor, Department of Mechanical Engineering, Jayamukhi Institute of Technological Sciences, Warangal, Telangana, INDIA

5_{Assistant Professor, Department of Mechanical Engineering, Malla Reddy College of Engineering and Technology,} Secundarebad, INDIA

ABSTRACT

Energy is an essential requirement for economic and social development of any country. Sky rocketing of petroleum fuel costs in present day has led to growing interest in alternative fuels like vegetable oils, alcoholic fuels, CNG, LPG, Producer gas, biogas in order to provide a suitable substitute to diesel for a compression ignition (CI) engine. The vegetable oils present a very promising alternative fuel to diesel oil since they are renewable, biodegradable and clean burning fuel having similar properties as that of diesel. They offer almost same power output with slightly lower thermal efficiency due to their lower energy content compared to diesel. Utilization of producer gas in CI engine on dual fuel mode provides an effective approach towards conservation of diesel fuel. Gasification involves conversion of solid biomass into combustible gases which completes combustion in a CI engines. Hence the producer gas can act as promising alternative fuel and it has high octane number and calorific value. Because of its simpler structure with low carbon content results in substantial reduction of exhaust emission. Downdraft moving bed gasifier coupled with compression ignition engine are a good choice for moderate quantities of available mass up to 500 kW of electrical power. Hence bio-derived gas and vegetable liquids appear more attractive in view of their friendly environmental nature.

Keywords-- Producer gas, Performance, Combustion, Emission, Characteristics

I.

INTRODUCTION

Biomass has been a major source of energy, even prior to the discovery of fossil fuels like coal and petroleum. Though its role is seen to be presently low key in the developed countries, it is still widely used in rural communities in the developing countries to serve energy needs for cooking and for limited industrial use.

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problem with producer-gas operated gas engines is power derating. A power drop from 40% to 70% can be expected [3].

II.

DOWNDRAFT GASIFIER

Gasifiers are the reactors in which gasification of solid fuel takes place giving Producer gas. This gasification is carried out in different types of gasifiers. These are downdraft, updraft and cross draft, fluidized, entrained bed, rotary and inclined grate. The most common gasifier is the downdraft or co-current type. The pyrolysis zone is above the combustion zone and the reduction zone below it. Fuel is fed from the top and the air flows in the downward direction through the combustion and reduction zones. Movement of air is in the same direction as that of the fuel. The downdraft gasifier is so designed that tars in the pyrolysis zone are drawn through the combustion zone wherein a high amount of them will be cracked and reduced to non-condensable gaseous products before leaving the gasifier. The internal diameter in most downdraft gasifiers is reduced in order to create throat. Air inlet nozzles are commonly set radially round the throat to distribute air as uniformly as possible [3].

Fig-1 Schematic view of a Downdraft Gasifier [3].

Fig-2 Photographic view of a Downdraft Gasifier [3].

III.

PERFORMANCE, COMBUSTION

AND EMISSION CHARACTERISTICS

3.1. Brake thermal efficiency (BTE)

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effect of lower calorific value of producer gas, combusted residual gases, low combustible temperature, and higher total fuel flow rate during combustion process. Also the reduction in BTE might be due to decreased flame propagation speed and increased negative compression work [6]. The BTE was found to be higher for HB-Producer gas operation over the entire load range with parallel carburetor. Producer gas being common, properties of the injected fuel has a major effect on the engine performance. The biodiesel injected fuel has higher viscosity than diesel which makes atomization difficult and also has lower calorific value, resulting in BTE. Among all the carburetors, parallel gas entry carburetor gives better performance compared with 30° and 60° degree gas entry carburetors. The BTE of HB-Producer gas operation for 30°, 60° and parallel flow gas entry carburetors were found to be 13.29%, 13.49%, 18.29% respectively [8]. BTE for producer gas-diesel dual fuel mode of operation was higher than ROME-Producer gas operation over the entire load range. That was mainly due to lower calorific value of ROME and producer gas. Lower flame velocity of producer gas during the ROME-Producer gas operation along with injected fuel has a major effect on the engine performance. The study with different combustion chamber shapes show that the ROME-Producer gas operation with TCC results in better performance compared to dual fuel operation with other combustion chambers. It may be due to the fact that, the TCC prevents the flame from spreading over to the squish region resulting in better mixture formation of ROME and along with producer gas-air combinations, as a result of better air motion and lowers exhaust soot by increasing swirl and tumble. The TCC has an ability to direct the flow field inside the sub volume at all engine loads and therefore substantial differences in the mixing process may not be present. The BTE values for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 16.8, 15.75, 17.01 and 17.45% compared to 18.65% for diesel-producer gas operation with respectively with HCC [9].

3.2. Brake specific energy consumption (BSEC)

With increased percentage of RRBO in the blends, SEC increased while brake thermal efficiency decreased at all the load. The decrease in brake thermal efficiency may be attributed to the lower energy content with increased concentration of RRBO in FD. At preheated blend (60°C) of RRBO and FD at the ratio of 1:1 and at 84% engine load SEC was lower and brake thermal efficiency was higher compared to other blends [1]. With increased percentage of Jatropha biodiesel in the blends, specific energy consumption increased. The decrease in specific energy consumption may be attributed to the more energy content with increased gas flow rate of wood chips producer gas in the combustion chamber. The diesel + B25 + Producer gas in mixed fuel mode shows the better performance than other combination of fuel [4]. The specific energy consumption in dual fuel mode operation is higher than

that of diesel mode in all operating conditions. Increase in specific energy consumption indicates that the efficiency reduces in the dual fuel mode. The increase of pilot diesel fuel amount leads to an improvement of the brake specific energy consumption compared to the one observed under lower pilot fuel quantity mode. The use of larger pilot fuel quantity leads to a higher total heat release rate during the premixed controlled combustion phase. It results to an increase of the cylinder charge temperature, which affects positively the combustion rate of diffusion phase since it becomes more efficient [5]. BSEC of the engine decreased with increase in the engine load for all the fuels tested. This was due to the higher percentage increase in brake power with increase in engine load as compared to the increase in fuel consumption due to relatively less heat losses at higher engine loads. Brake specific energy consumption in dual fuel mode was higher than that of single fuel mode at all load conditions and it increased with increase in fuel blends with HSD [6].

3.3. Exhaust gas temperature (EGT)

Exhaust gas temperature with Honge oil-producer gas dual fuel operation was higher for both modes of operation [2]. The EGT was found to be higher for Producer gas-Vegetable oils and lower for Producer gas-Diesel operation. The exhaust gas temperatures of 455, 485, 498 and 510°C were observed with Producer gas-diesel, Producer gas-Honge oil, Producer gas-Rice Bran oil and Producer gas-Neem oil respectively [3]. The exhaust gas temperature of dual fuel mode was always higher than that of diesel alone mode due to excess of energy supplied to the engine. Significantly higher combustion rates during the later stages with diesel-producer gas leads to higher exhaust gas temperature [5]. EGT increased with increase in engine load but decreased with increase in biodiesel concentration in the blends with diesel. The increase in EGT with engine load was mainly due to increase in the amount of energy released at higher loads because of the burning of increased amount of fuel which was injected to meet the extra power requirement to take up the additional loading; hence more heat rejection to the exhaust gases. The decrease in EGT for JB might be due to the poor combustion characteristics of the Jatropha biodiesel and its blends because of its viscosity variation. EGT in dual fuel mode was higher than that of single fuel mode at all load conditions. That might be due to the excess of energy supplied to the engine in dual fuel mode [6]. The Exhaust gas temperature was found to be higher for HB-Producer gas with 30° carburetor. That could be attributed to incomplete combustion of gaseous fuel and injected biodiesel burns during diffusion combustion phase. Parallel carburetor gave lower exhaust gas temperature compared with other carburetors tested. The Exhaust gas temperatures at full load with HB-Producer gas operation for 30°, 60° and Parallel carburetors were found to be 330, 326, 322 degrees respectively [8].

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output for all the fuel combinations was observed. It may be due to higher gas temperature and increase in temperature of inlet valve and combustion chamber walls. That feature decreases the density of induced air and hence the drop in volumetric efficiency. However, the part of the air replaced by producer gas further adds for that trend. Diesel-producer gas operation was resulted in better volumetric efficiency compared to ROME-producer gas combinations. It could be due to improper utilization of air as more ROME was injected for the same power generation with producer gas in dual fuel combinations. However, slightly higher volumetric efficiency was observed with TCC compared to other combustion chamber shapes. It may be due to the fact that, in case of TCC, at the end of compression stroke complete air-fuel mixture combination trapped in the cylinder and gets ignited immediately. At which almost piston reaches the TDC and squishes the fuel combination from the sides into the sub volume. Then the squish of the air and fuel mixture generates a very fast and turbulent velocity which results in to better combustion and utilizes complete air available in the combustion chamber. The volumetric efficiency for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 72.91, 72.12, 72.86 and 74.00% compared to 76.10% for diesel-producer gas operation with respectively with HCC [9].

3.5. Fuel substituted

There was an improvement in percentage of fuel substituted with all dual fuel combinations when operated with carburetor. Highest fuel substitution occurs with diesel-producer gas operation followed by HOME-producer gas operation with and without carburetor [2]. Fuel substitution values were maximum for diesel-Producer gas operation compared to vegetable oil combinations. Injected fuel properties such as cetane number, viscosity and calorific value may be considered as responsible for the observed trend. The percentage of respective fuels substituted with Producer gas-diesel, Producer gas-Honge oil, Producer gas-Rice Bran oil and Producer gas-Neem oil respectively were 71.00%, 54.00%, 64.50% and 50% [3]. Fuel substitution values were higher for TCC. TCC improves brake thermal efficiency and lowers specific fuel consumption. That means lesser fuel was consumed with TCC and hence allowing more producer gas burning for the same power output. The percentage of fuel substituted with TCC was 49% with ROME-producer gas and with HCC, CCC and TrCC’s and with ROME-producer gas were reported as 41, 43 and 49% respectively at 80% load. However, Maximum fuel saving was 56% for diesel-producer gas operation with HCC [9].

3.6. Diesel saving

The use of producer gas in dual fuel mode operation reduces the consumption of diesel fuel at all engine loads. The maximum diesel saving was 64.21% at the pilot diesel of 0.22 kg/h and Brake Mean Effective Pressure (BMEP) load of 535 kPa. The diesel saving was decreased at higher pilot diesel quantity. That

phenomenon was due to the mixture being richer at high pilot diesel and high engine loads [5].

3.7. Heat release rate (HRR)

The premixed burning phase associated with a higher heat release rate was significant with diesel-producer gas dual fuel operation. This is the reason for the higher thermal efficiency of Diesel-producer gas operation. The diffusion-burning phase indicated under the second peak was greater for Honge oil-producer gas and HOME-producer gas compared to diesel-producer gas dual fuel operation. That was consistent with the expected effects of vegetable oils viscosity on the fuel spray and reduction of air entrainment and fuel air mixing rates along with slow-burning producer gas. That leads to less fuel being prepared for rapid combustion with Honge oil-producer gas after the ignition delay. Therefore more burning occurs in the diffusion phase rather than in the premixed phase with Honge oil-producer gas. Significantly higher combustion rates during the later stages with Honge oil-producer gas leads to higher exhaust temperatures and lower thermal efficiency. However, HOME-producer gas operation shows improvement in heat release rate compared to neat Honge oil-producer gas dual fuel operation [2]. The maximum heat release rate for standard diesel, B10, B20 and B100 was 156.094, 122.702, 96.606 and 66.976 J/°CA, respectively. This was because of the shorter ignition delay; the premix combustion phase for neat Jatropha biodiesel and its blends was less intense. On the other hand, increased accumulation of fuel during the relatively longer delay period resulted in higher rate of heat release while running with diesel. For B10, B20 blends, the heat release peak was higher than that of B100 due to reduced viscosity and better spray formation. In dual fuel combustion, the rate of heat release was lower compared to single fuel combustion and it decreased with increase in biodiesel blends. The gaseous fuel with the intake-air charge brought about a decrease and dilution of oxygen concentration, a decrease of charge air temperature at the time of starting pilot injection due to the lower polytropic index of producer gas and the pre-ignition reactions of the producer gas-air residual gas mixtures during the intake and compression processes. These principal factors might have caused ignition delay to extend [6]. ROME-Producer gas operation for HCC, CCC and TrCC results in lower heat release rate compared to the operation with TCC. This is due to the result of higher second peak obtained HCC, CCC and TrCC in the diffusion combustion phase compared to the dual fuel operation with TCC operation [9].

3.8. Cylinder pressure

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period and spray envelope of the injected fuel. The viscosity and volatility of the fuel had important role to increase atomization rate and to improve air fuel mixing formation. Because of the high viscosity and low volatility of Jatropha biodiesel and its blends, the cylinder peak pressure for these fuels was lower than that of standard diesel. The peak pressure was observed to be 71.261, 70.371, 69.764, 64.355, 70.337, 69.816, 67.571 and 62.531 bar for standard diesel, B10, B20, B100, DPG, B10PG, B20PG and B100PG, respectively [6]. Higher peak pressure was observed with TCC compared to HCC, CCC and TrCC. This may be due to better burning of the fuel combination at rapid combustion phase and decreased diffusion combustion phase occurring at higher CR. However, with same combustion chamber (HCC), peak pressure with ROME-producer gas combination under dual fuel mode of operation was found to be lower compared to diesel-producer gas operation. This may be due to combined effect of lower calorific value of ROME and producer gas, lower flame velocity, higher viscosity and density of ROME leading to poor combustion at rapid combustion phase. The peak pressure obtained for ROME-producer gas combination at 15, 16 and 17.5 CR were 65, 69.89 and 71.8 bar compared to 77 bar for diesel-producer gas operation respectively [9].

3.9. Combustion duration

The combustion duration increases with increase in the power output with all combustion chamber shapes. This is due to the amount of fuel being burnt inside the cylinder gets increased. Combustion chamber being same, higher combustion duration was observed with ROME-Producer gas combination compared to diesel-producer gas operation. It is could be due to higher viscosity of ROME leading to improper air-fuel mixing, and needs longer time for mixing and hence resulting incomplete combustion with longer diffusion combustion phase. Lower adiabatic flame temperature of producer gas and high viscosity of ROME and reduced heat release rate obtained with ROME-Producer gas are also responsible for that trend. The combustion duration for ROME-Producer gas operation was reduced and improved with TCC compared to other combustion chambers tested. That could be attributed to improvement in mixing of fuel combination due to better squish. Significantly higher combustion rates with ROME-Producer gas operation leads to higher exhaust temperatures and lower thermal efficiency. However, ROME-Producer gas operation with TCC shows improvement in heat release rate compared to the operation of ROME-Producer gas operation with other combustion chamber shapes. The combustion duration obtained for ROME-producer gas combination with HCC, CCC, TrCC and TCC were found to be 39.8, 39.65, 38.45 and 38.25°CA compared to 35.8°CA for diesel-producer gas operation with HCC respectively [9].

3.10. Ignition delay

For all the fuel tested ignition delay decreased with increase in system load. Increasing the load increased the residual gas and wall temperature which resulted in a higher charge temperature at injection and hence decrease in the ignition delay. Ignition delay decreased with increase in concentration of biodiesel in biodiesel blends with diesel. That was mainly due to the shortening of the physical delay and also the high cetane number of biodiesel. The oxygen present in the fuel increased the air fuel mixing rate which reduces the physical delay and higher cetane number of fuel started the ignition earlier. In dual fuel mode of operating an engine, the admission of a gaseous fuel with the air influenced profoundly both the physical and chemical ignition processes of the mixture. Its induction would bring about variations in the physical properties of the mixture such as the specific heat ratio and heat transfer parameters. These could lead to significant changes in the charge temperature and pressure levels at the time of fuel injection and extend the physical ignition delay period of the mixture. In dual fuel mode ignition delay was highest for DPG followed by B10PG, B20PG and B100PG [6]. Dual fuel operation with ROME-producer gas operation and with different combustion chamber shapes show variations in an ignition delay. Ignition delay was decreased with an increase in brake power for almost all combustion chamber shapes. With an increase in brake power, the amount of fuel being burnt inside the cylinder gets increased and subsequently the temperature of in-cylinder gases gets increased. That leads to reduced ignition delay with all combustion chamber shapes. However, the ignition delay for diesel-producer gas combination was lower with HCC compared to ROME-producer gas operation with combustion chamber shapes. With same combustion chamber (HCC), ROME-producer gas operation show longer ignition delay compared to diesel-producer gas operation. That may be due to the variations in the air-producer gas mixture, lower calorific value of both ROME and producer gas, lower flame temperature of producer gas, higher viscosity of ROME. Hence it requires more time for burning. However, lower ignition delays were observed for ROME-producer gas operation with TCC compared to the operation with HCC, CCC and TrCC. It could be attributed to better air-fuel mixing and increased combustion temperature. The ignition delay obtained for ROME-producer gas combination with HCC, CCC, TrCC and TCC were found to be 19.8, 18.56, 17.12 and 16.25°CA compared to at 14.9°CA for diesel-producer gas operation with HCC respectively [9].

3.11. Smoke opacity

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atomization of injected fuel, leading to better combustion [2]. The smoke emission in dual fuel operation was comparatively lower as compared to neat diesel, Honge and Neem oil operation. In dual fuel mode increase in smoke density was observed with the increase in Producer gas flow rate. The better combustion with Honge oil in both the single and dual fuel modes was observed and was due to better atomization and mixture preparation with air resulting in lower smoke followed by Rice Bran and Neem oils [3]. Smoke opacity in case of turbo mode of all test fuels was lower than their natural aspirated mode. That was due to better combustion of fuel as a result of availability of sufficient fresh air supplied by turbocharger. The percentage decreases in smoke opacity of FD, K10 and K20 with turbo mode were 8.6%, 4.7% and 5.12% respectively compared to their natural aspirated mode. However, with increase in load, the smoke opacity values of all test fuels increases in both modes of operation. That may be due to incomplete combustion as result of rich mixture formed with increase in load [7]. The smoke opacity for Producer gas-diesel dual fuel operations was lower than ROME-Producer gas over the entire load range. That may be due to improper fuel-air mixing due to higher viscosity of ROME and higher free fatty acid content of ROME. TCC gives lower smoke emission levels compared to other combustion chambers. It may be due to the fact that, the prevailing air-fuel mixing and higher turbulence in the combustion chamber result better combustion and oxidation of the soot particles which further reduce the smoke emission levels. The smoke emission levels for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 51, 58, 42, and 35 HSU compared to 32 HSU for diesel-producer gas operation with respectively with HCC [9].

3.12. Hydrocarbon (HC) emissions

Highest HC emission was obtained with Honge oil-producer gas dual fuel operation. The lower calorific value and higher viscosity of Honge oil in the presence of slow-burning producer gas results in the highest HC emissions [2]. At lower loads HC emissions were lower and found to increase with the load. HC emissions trend was similar for both single fuel and dual fuel modes of operation. Hydrocarbon emissions were higher throughout the load range for the injected vegetable oils compared to Producer gas-diesel [3]. HC emissions in general increased with increase in engine load. At higher load, the excess fuel required to meet the power requirement resulted in decreased air-fuel ratio, consequently increasing the HC emissions sharply. HC emissions were found to be lower for JB and its blends as compared to HSD over the entire range of engine loads. The reduction in HC emissions for biodiesel blends might be due to the presence of oxygen content in the biodiesel molecule, which led to a more complete and cleaner combustion. The HC emission in dual fuel mode was found to be higher than single fuel mode at each load and it decreases with increase in biodiesel

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gas operation respectively with HCC [9].

3.13. Carbon monoxide (CO) emissions

The exhaust emissions of carbon monoxide were lower for diesel-producer gas dual fuel operations compared to Honge-producer gas and HOME-producer gas operation. That may be due to higher heat release rate leading to better combustion with producer gas-diesel mixture [2]. The exhaust emissions of carbon monoxide were lower for neat single fuel operations compared to dual fuel operation. Higher concentration of CO in the exhaust was a clear indication of incomplete combustion of the premixed mixture. The CO levels were higher due to combustion inefficiencies. The mixture of Producer gas-air flow to the engine reduces the amount of oxygen required for complete combustion and that creates incomplete combustion and increase in the CO emissions. Higher emission of CO in dual fuel mode could be attributed to lower heating value of Producer gas, lower adiabatic flame temperature and lower mean effective pressures [3]. The CO emission in a producer gas-diesel dual fuel mode was always higher than that of the diesel alone mode at all operations. The increase of pilot fuel amount, keeping the engine load constant, leads to a decrease of CO emissions. A larger pilot fuel quantity provides a greater magnitude of ignition centers with large reaction zones. Moreover the flame propagation path from each ignition center within the charge becomes relatively shorter, and thus, combustion was better. At higher loads, when the gaseous fuel concentration in the air charge was above the lean combustion limit, the frame was able to propagate through most of the combustion chamber unaided and varying the pilot fuel quantity has little effect [5]. CO initially decreased with increase in engine load and then it increased with further increase in engine load for all the fuels tested. Initially, at lower engine loadings, cylinder temperature might be too low, which increased with engine loading due to higher quantity of heat release during the burning of higher quantity of fuel injected inside the cylinder. The increased cylinder temperature at higher engine loads prompted relatively better burning of the fuel resulting in decreased CO. However, with further increase in engine load beyond 80%, CO emission increased due to incomplete combustion of the excess fuel injected into the combustion chamber owing to lower air-fuel ratio which might have prevented oxidation of CO into CO2. The emission of CO decreased with increasing proportion of jatropha biodiesel in the fuel blends. That was due to the presence of more inbuilt oxygen in the blends with higher biodiesel concentration, which led to relatively better combustion of the fuel resulting in lower CO emission. Further much higher values of CO emission were recorded in dual fuel mode as compared to single fuel mode. The higher concentration of CO emission in the dual fuel mode gave an indication of incomplete combustion. The mixture of high temperature PG and air flow to the engine reduced the amount of oxygen required for complete combustion. That created

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higher HC and CO emission levels. However, combustion with ROME-Producer gas operation with TCC resulted in lower HC and CO emission levels compared to other combustion chamber shapes. It could be due to higher turbulence and comparatively higher temperature in the combustion chamber, minimum heat losses and better oxidation of HC and CO improved and which reduces the both emission levels i.e. better combustion of ROME with better mixture formation of ROME and air along with producer gas due to improved swirl motion of air. Also, higher oxygen present in the ROME leads to better combustion with TCC. However, other combustion chambers may not contribute to the proper mixing fuel combinations; it may be due to confinement in the inferior part of the bowl by the vortex generated by the HCC, CCC and TrCC. The HC levels for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 44, 55, 48 and 46 ppm, compared to 38 ppm for diesel-producer gas operation respectively with HCC. Similarly, CO levels for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 0.46, 0.42, 0.39 and 0.37% compared to 0.31% for diesel-producer gas operation respectively with HCC [9].

3.14. Nitrogen oxide (NOx) emissions

There is an improvement in NO level with all dual fuel combinations when operated with carburetor. Highest NO emission was obtained with Honge oil-producer gas dual fuel operation. Nitrogen oxide emissions in dual fuel mode do not vary significantly with the change in injected fuel. At maximum power developed by the engine the NOx emissions were in the range of 130-195 ppm. NOx emissions were lower for diesel-producer gas dual fuel operation. Nitrogen oxide emissions in dual fuel mode of operation were 130 ppm, 195 ppm and 175 ppm with diesel, Honge oil and HOME as injected fuel, respectively. Higher NOx emissions for Honge-producer gas oil dual fuel operation may be due to availability of higher oxygen that is present in the Honge molecular structure [2]. The nitrogen oxides emissions for dual fuel mode were significantly lower. That may be due to the lower adiabatic flame temperature of Producer gas and absence of organic nitrogen in Producer gas. Nitrogen oxides emissions in dual fuel mode do not vary significantly with the change in injected fuel. NOx emissions were lower for Producer gas-diesel dual fuel operation. Nitrogen oxide emissions in dual fuel mode of operation were 130 ppm, 195 ppm 200 ppm and 212 ppm with diesel, Honge oil, Rice Bran and Neem oils as injected fuel respectively. Higher NOx emissions for injected vegetable oils in dual fuel operation may be due to availability of higher oxygen that is present in the injected vegetable oils molecular structure. Also for the same power output more vegetable oils are required (due to increased specific fuel consumption) leading to delayed injection [3]. The NOx concentration in emission increased with increase in engine load for all the fuels tested. As the engine load increased, average gas temperature in the combustion chamber also

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combustion phase occurs with diesel-producer combination compared to ROME-Producer gas combination. Slightly higher NOx is resulted from ROME-producer operation with TCC compared to the operation with other combustion chambers tested. This could be due to slightly better combustion occurs due to more homogeneous mixing and larger part of combustion occurs just before top dead center. Presence of oxygen in a ROME is also responsible for that trend. Therefore it is resulted in higher peak cycle temperature. The NOx emission levels for ROME-PG operation with HCC, CCC, TrCC and TCC were found to be 90, 65, 88 and 95 ppm, compared to 109 ppm for diesel-producer gas operation respectively with HCC [9].

3.15. Carbon dioxide (CO2) emissions

The CO2 emission in general increased with increase in engine load. As the amount of fuel injected into the combustion chamber increased with engine load, quantity of fuel going through complete combustion also increased which resulted in increase in cylinder temperature. At elevated temperature, performance of the engine improved with relatively better burning of the fuel resulting in higher CO2 emission. The CO2 emission in general was found to be increased significantly with increase in concentration of biodiesel in the fuel blends at any engine load tested. This could be attributed to the increase in the mass of fuel injected into the combustion chamber for biodiesel blends and better combustion of the injected fuel owing to the inherent oxygen present in the jatropha biodiesel. CO2 emission in dual fuel mode was higher than that of diesel mode at all load conditions and it increased with increase in fuel blends with HSD. The reason of increasing CO2 is that the producer gas is a mixture of CO, HC, CH4 and CO2. Therefore the combustion in the engine of the producer gas increases the carbon dioxide emission [6]. The CO2 emission in turbo mode operations of all test fuels is higher than without turbo mode operations at all load conditions. This is an indication of higher oxidation of CO into CO2 and complete combustion of cylinder charge with addition of sufficient air by turbocharger compared to natural aspirated mode. The percentage increase in CO2 emission in turbo mode operation of FD, K10 and K20 are 6.7%, 5.17% and 5.67% respectively compared to their natural aspirated mode at full load condition. CO2 emissions of both blended fuels are lower than diesel under all test conditions. With increase in load, CO2 emission increases for all test fuels for both modes of operations due to better combustion as a result of higher charge temperature. Similarly, with increase in gas flow rate, the CO2 emission for all test fuels increases under all test conditions. Since producer gas contains CO2, its addition during combustion increases the percentage of CO2 emission. With increase in gas flow rate from 10.74 kg/hr to 15.21 kg/hr, increase in CO2 emissions are 0.3%, 0.5% and 0.5% for FD, K10 and K20 respectively in natural aspirated mode and corresponding increase in values in turbo mode operation are 0.23%, 0.43% and 0.7% respectively. With increase in blend percentage in

diesel, CO2 emission decreases marginally at all gas flow rates. The possible reason is due to higher viscosity and poor atomization characteristic of blended fuels causing incomplete combustion and leading to lower CO2 emission [7]. Higher carbon dioxide emissions due to incomplete combustion and due to higher oxygen content in biodiesel. 60° carburetor ensures supply of stoichiometric mixture of air and producer gas compared to other carburetors used and this ensures better combustion as well. The carbon dioxide emission values at full load for HB-Producer gas operation with 30°, 60° and parallel carburetors were found to be 8.5, 6.9 and 7.2 respectively [8].

IV.

CONCLUSIONS

From exhaustive literature survey following conclusions are made;

 The brake thermal efficiency of engine with single fuel operation was always more than dual fuel mode of operation.

 Smoke/NO emissions of producer gas-injected fuels in dual fuel engine were found to be lower than single fuel engines.

 HC/CO emissions of producer gas-injected fuels in dual fuel engine were found to be more than single fuel engine operation.

 Specific energy consumption was found to be minimum in mixed fuel mode.

 The ignition delays of dual-fuel mode operation for both the fuels were longer than for single-fuel mode operation

 In dual-fuel mode, the peak pressure and HRR for producer gas-biodiesel dual-fuel were slightly lower than those of producer gas-diesel combustion at full load condition.

 The exhaust gas temperatures were slightly higher for dual-fuel mode of operation compared to single-fuel modes.

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[2] Banapurmath NR, Tewari PG. Comparative performance studies of a 4-stroke CI engine operated on dual fuel mode with producer gas and honge oil and its methyl ester (HOME) with and without carburetor. Renewable Energy 2009;34:1009-1015.

[3] Banapurmath NR, Tewari PG, Yaliwal VS, Kambalimath S, Basavarajappa YH. Combustion characteristics of a 4-stroke CI engine operated on Honge oil, Neem and Rice Bran oils when directly injected and dual fuelled with producer gas induction. Renewable Energy 2009;34:1877-1884.

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Technology 2012;1(3):1-6.

[5] Sombatwong P, Thaiyasuit P, Pianthong K. Effect of Pilot Fuel Quantity on the Performance and Emission of a Dual Producer Gas-Diesel Engine. Energy Procedia 2013;34:218-227.

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[7] Nayak C, Acharya SK. Experimental Investigation of Diesel Engine Emissions with Producer Gas and Blends of Neat Karanja Oil as Fuel Adding Turbocharger. International Journal of Renewable Energy Research 2014;4(3):675-682.

[8] Hadkar T, Amarnath HK. Performance and Emission Characteristics of Producer Gas derived from Coconut Shell (Biomass) and Honne Biodiesel with different Configuration of carburetor for dual fuel four stoke direct injection diesel engine. International Research Journal of Engineering and Technology 2015;2(3):1804-1811.