Hydrogen enrichment on diesel engine with biogas in dual fuel mode

https://doi.org/10.1016/j.ijhydene.2019.12.167Get rights and content

Highlights

  • Hydrogen gas production by new alkaline electrolyzer.

  • Generation of biogas in modified RCC KVIC plant.

  • Effect of novel fuel blend (hydrogen, biogas and diesel) on dual fuel engine performance and emissions.

  • Optimization of injection timing for selected optimum novel hydrogen-biogas-diesel fuel blend.

Abstract

Fossil fuels fulfill a major part of the world's energy demand. Higher demand for energy, depletion of fossil fuels and environmental impacts are the key motivational factors to explore alternate energy sources. Biogas and Hydrogen seem to be the promising alternate gaseous fuels. In this paper, the performance and emission studies were performed on a stationary dual fuel engine using fuel combinations of diesel, biogas-diesel, hydrogen-diesel, and hydrogen-biogas-diesel. Experimental results reveal that the performance of dual fuel mode with hydrogen-biogas-diesel fuel improved, and emissions were reduced in comparison to the neat diesel operation. The Brake Thermal Efficiency (BThEff) was improved by 3.09%, Brake Specific Diesel Consumption (BSDC) was reduced by 71.05%, and Brake Specific Energy Consumption (BSEC) decreased by 12.13%. The emission parameters CO, HC, and NOx, were reduced by 88.09%, 5.68%, and 83.01% respectively. Injection timing, which was obtained at 21°CA BTDC, was optimized experimentally for the selected optimum hydrogen-biogas-diesel fuel.

Introduction

The energy demand of the world is growing continuously. It is fulfilled mainly through the supply of fossil fuels viz. Coal, petroleum oils, and natural gas. The fossil fuels are available in the concentrated form, and these are economical as compared to other alternative fuel sources. However, these are depleting very fast. Combustion of fossil fuel creates environmental pollution, by emitting harmful pollutants like CO, CO2, HC, NOx, SOx, heavy metals, and ashes, etc. Vehicles, manufacturing, process industry, coal-fired power plants are immediate sources of harmful exhaust gases [1]. The adverse effect on the urban air quality due to diesel engine exhaust NOx and particulate matter emission are linked to a rise in the premature mortality. The exhaust gases collected in the atmosphere cause the greenhouse effect. The undiscriminating utilization of fossil fuel is a prime reason for global warming. It is affecting mankind and living beings unfavorably [2,3]. The continuous rise in the prices of the petroleum products due to higher demand and environmental hazards are the reasons for the scientists to explore the alternate fuel resources which can be used in the existing setup without modifications. Researchers are working on the other alternatives for the gasoline-based engines, either running solely on alternative sources viz. Biogas, syngas, producer gas or with hydrogen blending [4,5].

Rehman et al. studied the effect of injection strategies for common rail biogas-diesel dual fuel engine. The methane percentage in biogas varies between 24 and 68%. The diesel engine can be easily operated in biogas-diesel dual fuel mode without any modification. If the biogas energy share is below 60%, the performance and emission parameters can be significantly optimized by adjusting the injection timing. Diffused combustion of post-injected fuel takes place in biogas-diesel dual fuel operation. It results in decrease in NOx and increase in CO2 emissions due to low in-cylinder temperature. Smoke emission is decreased due to improved charge homogeneity by the split injection process [6,7].

The emission of CO and HC diminished remarkably due to lean fuel mixture combustion. It presents clean and effective combustion in comparison to neat diesel and gasoline. Biogas is lighter than air, which is an innate property of the biogas. The primary issue associated with the biogas is the space requirement for production and storage. So, mostly it is used in the stationary engines [8].

In the last several years, hydrogen has been explored as a suitable alternative fuel. Hydrogen production is based on water splitting, which is both more environment-friendly and sustainable, such as processes of thermolysis, thermochemical processes, electrochemical processes, photochemical processes, and photocatalyst processes [9,10]. In view of today's environmental and energy issues, water electrolysis can provide an effective, clean and promising alternative hydrogen production technology [11]. It enhances the thermal efficiency of the engine, close to no pollution [12]. Hydrogen has higher laminar flame speed and wide flammability range. Its properties and molecular structure have made it suitable for the IC engine application [13]. In comparison to the standard fossil fuel based energy sources, hydrogen is a carbonless fuel. Combustion of hydrogen does not produce HC, CO and CO2, which is the case in hydrocarbon fuel. In hydrogen-diesel dual fuel mode, there is reduction in CO2 and particulate matter with an increase in the hydrogen share. As the hydrogen share reaches above 10% of the total energy input, NOx increases. A programmable hydrogen augmentation system controlled through the accelerator pedal is developed for Hydrogen augmentation which reduces the CO and NOx emissions on the cost and increases in the particulate matter emission [14].

Juknelevičius et al. investigated the co-combustion process of hydrogen in dual fuel mode. The influence of hydrogen energy shared on auto ignition delay, combustion intensity at the premixed phase and in-cylinder pressure are studied at various loads. The impact of different hydrogen flow rates at fixed injection timing on the combustion of the CI engine is studied and validated through the developed AVL boost model. No significant change is observed in combustion duration with low hydrogen energy share while reduction of in-cylinder pressure is associated with deterioration on BTE and BSFC at low load condition [15].

Karagoz et al. presented the hydrogen injection method in the intake manifold using the ECU controlled LPG-CNG injector. The effect of 0%, 22%, and 53% hydrogen addition of total energy supplied on emission and performance characteristics are experimentally investigated [16]. When hydrogen is supplied to heavy duty hydrogen-diesel dual fuel engine at a low load, with hydrogen energy share of up to 98% without any implications, it results in the reduction of carbon and NOx emissions above 90% while soot emissions are dropped by 85%. The primary challenge is increase in NOx emission at a medium load [17]. The dual fuel CI engine is operated on hydrogen-biodiesel (BD40) with 10% exhaust gas recirculation at full load. The BThEff is improved by 21.9% and a significant decrease in smoke opacity is observed [18]. Effect of addition of hydrogen-hydroxy gas with microalgae biodiesel gives rise to brake power, torque and reduced CO2 emission [19].

Yadav et al. studied the performance and emission characteristics of the single cylinder direct injection CI engine in diesel-hydrogen dual fuel mode. Hydrogen enriched air is used for the fresh charge intake using carburation technique with 10% and 20% EGR, which shows improved emission and boost in the performance [20]. The injection timing is optimized for different hydrogen flow rates (80 g/h, 120 g/h, 150 g/h). It varies between 18.5° and 27.5°CA BTDC with a gradient of 1.5°CA. The optimum BThEff and BSEC are observed at an injection timing of 20°CA BTDC with a hydrogen flow rate of 120 g/h [21]. The BThEff is improved by 10.71% at 20°CA BTDC, which reduces the BSEC by 11.6% compared to neat diesel operation [22].

Verma et al. presented energy and exergy analyses for diesel-biogas dual fuel engine. The performance and emission parameters are analysed for change in CR (16.5–19.5), EGR and EGR temperatures. Higher CR is advantageous for the engine performance and emission, dual fuel engine is studied at CR of 19.5 and the effects of EGR are analysed. At a low load, it slightly improves the engine efficiency and decreases the NOx emissions. However, high EGR percentages at high loads showed slight decrease in engine efficiency. For hot EGR, the dual fuel engine has shown highest efficiency both at low and high loads [23].

Exergoeconomic analysis of biogas-based gas turbine system with preheater is studied. Fuel pricing definition is derived on two basis - one on the exergy and another on the LHV. Exergetic efficiency decreases with reduction in methane content [24]. Bora and Shah optimized the CR and injection timing for the dual fuel engine. Injection timing is varied from 26° to 32° CA BTDCs at the step of 3° whereas CA and CR is varied from 18 to 16 at different loading conditions. Pilot fuel injection timing of 29° BTDC and CR of 18 were found to be optimum with a maximum BThEff of 25.44% along with a liquid fuel replacement of 82.11% [25].

Biogas is a prominent alternate fuel, generated locally and can be used in dual fuel mode with diesel. However, there are certain challenges including a reduction in the performance of the engines and rough running of the engine while replacing diesel with a higher rate. Hydrogen has no carbon content, high flame speed, low ignition delay, wide flammability range and small quenching distance. Hence, the impact of hydrogen gas addition on the performance of a single cylinder CI engine fuelled with diesel, biogas-diesel was investigated. The performance and emission studies were conducted and compared for diesel, biogas-diesel, hydrogen-diesel, hydrogen-biogas-diesel. Optimum injection timing was also determined experimentally for the selected optimum blend.

Section snippets

Materials and methods

It consists of three sections, explaining the production of the hydrogen from water electrolysis, production of the biogas and IC engine test setup.

Results & discussion

The experimental testing was performed at a constant engine speed of 1500 rpm. The engine was tested for conventional and dual fuel operation on different loads. The load range was 0–14 kg with a step of 2 kgs. The performance parameters viz. BThEff, BSDC, BSEC, volumetric efficiency were calculated. Emission parameters viz. CO2, CO, unburnt HC, NOx, oxygen, and temperature of the exhaust were also measured. The biogas and hydrogen were supplied at a constant flow rate of 1283.86 l/h and 18 l/h

Conclusions

Experimental studies were performed successfully on a four-stroke, single cylinder CI engine dual fuel mode with load range (0–14 kgs.). The impact of hydrogen addition on performance and emission of biogas-diesel dual fuel engine were analysed, which reveal hydrogen-biogas-diesel was an optimum blend. Following conclusions were made from the experimental studies:

  • The BThEff was increased by 3.09% in hydrogen-biogas-diesel at an optimum load of 12 kgs. CI engine was running smoothly on

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