A comprehensive study on performance,emission and combustion behavior of a compression ignition engine fuelled with WCO (waste cooking oil) emulsion as fuel

This work aims at evaluating the performance, emission and combustion of a diesel engine fuelled with WCO (waste cooking oil obtained from palm oil) and its emulsion as fuel. A single cylinder water-cooled diesel engine was used. Base data was generated with diesel and neat WCO as fuels. Subsequently, WCO oil was converted into its emulsion and tested. Neat WCO resulted in higher smoke, hydrocarbon and carbon monoxide emissions as compared to neat diesel. Significant reduction in all emission was achieved with the WCO emulsion. Cylinder peak pressure and maximum rate of pressure rise were found to be higher with WCO emulsion as compared to neat WCO mainly at high power outputs. Ignition delay was found as higher with neat WCO and its emulsion. It is concluded that WCO emulsion can be used in diesel engines without any modifications in the engine with superior performance and reduced emissions at high power outputs.     

Impact of oxygen enrichment on the engine's performance,emission and combustion behavior of a biofuel based reactivity controlled compression ignition engine

Diesel engine with RCCI (Reactivity Controlled Compression Ignition) finds the next generation technology in engine research for combusting slow burning fuels such as vegetable oils and arriving extremely lower levels of smoke and NO (Nitric Oxide) emissions simultaneously. An attempt was made to operate a diesel engine on RCCI mode by injecting ethanol as low reactivity fuel at the intake manifold of the engine using sunflower based Waste Cooking Oil (WCO) as high reactivity fuel under oxygen enriched intake air. The influence of the combined effect of oxygen enrichment and RCCI mode on engine's behavior was studied using WCO as the high reactivity (main) fuel. Significant improvement (upto 33.5% with RCCI mode from 29.1% with neat WCO at peak power) in BTE (brake thermal efficiency) with drastic reduction in smoke (upto 48% with RCCI at the maximum efficiency point from 69% with neat WCO at peak power) and NO were achieved with injection of ethanol under RCCI mode when using WCO as base fuel mainly at high loads (power outputs). Combining oxygen enrichment with RCCI resulted in further improvement in BTE (upto 36.2%) and reduction in smoke (upto 37% at the maximum efficiency point), HC and CO emissions at all power outputs. Peak pressure and energy release rate were found to be superior with RCCI mode with EF (electronic fuel) injection of ethanol associated with oxygen enriched combustion. It is concluded that RCCI operation with injection of ethanol combined with oxygen enrichment could be preferred for very high BTE, lowest smoke and NO emissions using WCO as base fuel. The optimal level of low reactivity fuel blending with high reactivity WCO could be at the ethanol energy share of 25% for the highest thermal efficiency at peak load. The optimal oxygen concentration of 23% by volume could be preferred for best performance of the engine fueled with WCO as main fuel.     

Performance and combustion characteristic of CI engine fueled with hydrogen enriched diesel

The combustion of hydrogen–diesel blend fuel was investigated under simulated direct injection (DI) diesel engine conditions. The investigation presented in this paper concerns numerical analysis of neat diesel combustion mode and hydrogen enriched diesel combustion in a compression ignition (CI) engine. The parameters varied in this simulation included: H₂/diesel blend fuel ratio, engine speed, and air/fuel ratio. The study on the simultaneous combustion of hydrogen and diesel fuel was conducted with various hydrogen doses in the range from 0.05% to 50% (by volume) for different engine speed from 1000 – 4000 rpm and air/fuel ratios (A/F) varies from 10 – 80. The results show that, applying hydrogen as an extra fuel, which can be added to diesel fuel in the (CI) engine results in improved engine performance and reduce emissions compared to the case of neat diesel operation because this measure approaches the combustion process to constant volume. Moreover, small amounts of hydrogen when added to a diesel engine shorten the diesel ignition lag and, in this way, decrease the rate of pressure rise which provides better conditions for soft run of the engine. Comparative results are given for various hydrogen/diesel ratio, engine speeds and loads for conventional Diesel and dual fuel operation, revealing the effect of dual fuel combustion on engine performance and exhaust emissions.     

Hydrogen dual-fuelling of compression ignition engines with emulsified biodiesel as pilot fuel

Dual-fuel compression ignition (CI) engine operation with hydrogen is a promising method of using hydrogen gas in CI engines via high-cetane pilot fuel ignition. However, hydrogen dual-fuel operation with neat pilot fuels typically produce: high NO_x emissions; and high combustion chamber pressure rise rates (leading to increased “Diesel knock” tendencies). While water-in-fuel emulsions have been used during normal CI engine operation to cool the charge and slow combustion rates in an effort to reduce NO_x emissions, these water-in-fuel emulsions have not been tested as pilot fuels during hydrogen dual-fuel combustion. In this work two water-in-biodiesel emulsions are tested as pilot fuels during hydrogen dual-fuel operation. Hydrogen dual-fuel operation generally produces at best comparable thermal efficiencies compared with normal CI engine operation, while the emulsified biodiesel pilot fuels generally increase thermal efficiencies when compared with the neat biodiesel pilot fuel during dual-fuel operation. There is also a clear reduction in NO_x emissions with emulsified pilot fuel use compared with the neat pilot fuel. The thermal efficiency increase is more apparent at higher engine speeds, while the NO_x reduction is more apparent at lower speeds. This is due to two conflicting effects (exclusive to emulsified pilot fuel) that occur in tandem. The first is the cooling effect of water vapourisation on the charge, while the second is the microexplosion phenomenon which enhances fuel-air mixing. The NO_x emission reduction is due to the emulsified pilot fuel lowering pressure rise rates compared with the neat pilot fuel, while the efficiency increase is due to a more homogeneous charge resulting from the violent microexplosion of the emulsified pilot fuel. Smoke, CO, HC and CO₂ emissions remain comparable to neat pilot fuel tests. Overall, emulsified pilot fuels can reduce NO_x emissions and increase thermal efficiencies, however not at the same instance and under different operating conditions. The general trends of reduced power output, reduced CO₂ and increased water vapour emission during hydrogen dual-fuel operation (with neat pilot fuels) are also maintained.     

A renewable pathway towards increased utilization of hydrogen in diesel engines

In the present work, dual fuel operation of a diesel engine has been experimentally investigated using biodiesel and hydrogen as the test fuels. Jatropha Curcas biodiesel is used as the pilot fuel, which is directly injected in the combustion chamber using conventional diesel injector. The main fuel (hydrogen) is injected in the intake manifold using a hydrogen injector and electronic control unit. In dual fuel mode, engine operations are studied at varying engine loads at the maximum pilot fuel substitution conditions. The engine performance parameters such as maximum pilot fuel substitution, brake thermal efficiency and brake specific energy consumption are investigated. On emission side, oxides of nitrogen, hydrocarbon, carbon monoxide and smoke emissions are analysed. Based on the results, it is found that biodiesel-hydrogen dual fuel engine could utilize up to 80.7% and 24.5% hydrogen (by energy share) at low and high loads respectively along with improved brake thermal efficiency. Furthermore, hydrocarbon, carbon monoxide and smoke emissions are significantly reduced compared to single fuel diesel engine operation. Exhaust gas recirculation (EGR) has also been studied with biodiesel-hydrogen dual fuel engine operations. It is found that EGR could improve the utilization of hydrogen in dual fuel engine, especially at the high loads. The effect of EGR is also found to reduce high nitrogen oxide emissions from the dual fuel engine and brake thermal efficiency is not significantly affected.     

Influence of operating parameters on performance and emissions for a compression-ignition engine fueled by hydrogen/diesel mixtures

Hydrocarbon exhaust emissions are mainly recognized as a consequent of carbon-based fuel combustion in compression ignition (CI) engines. Alternative fuels can be coupled with hydrocarbon fuels to control the pollutant emissions and improve the engine performance. In this study, different parameters that influence the engine performance and emissions are illustrated with more details. This numerical work was carried out on a dual-fuel CI engine to study its performance and emission characteristics at different hydrogen energy ratios. The simulation model was run with diesel as injected fuel and hydrogen, along with air, as inducted fuel. Three-dimensional CFD software for numerical simulations was implemented to simulate the direct-injection CI engine. A reduced-reaction mechanism for n-heptane was considered in this work instead of diesel. The Hiroyasu-Nagel model was presented to examine the rate of soot formation inside the cylinder. This work investigates the effect of hydrogen variation on output efficiency, ignition delay, and emissions. More hydrogen present inside the engine cylinder led to lower soot emissions, higher thermal efficiency, and higher NO_x emissions. Ignition timing delayed as the hydrogen rate increased, due to a delay in OH radical formation. Strategies such as an exhaust gas recirculation (EGR) method and diesel injection timing were considered as well, due to their potential effects on the engine outputs. The relationship among the engine outputs and the operation conditions were also considered.     

Synergistic effect of hydrogen induction with biofuel obtained from winery waste (grapeseed oil) for CI engine application

The purpose of this study is to experimentally investigate the use of grapeseed oil as a fuel substitute obtained from biomass waste from winery industry and the synergic effect of hydrogen addition for compression ignition engine application. The experiments were carried out in a single cylinder, four stroke diesel engine for various loads and energy share of hydrogen. Combustion, performance and emission characteristics of grapeseed biodiesel, neat grapeseed oil and diesel have been analysed and compared with the results obtained with hydrogen induction in the intake manifold in dual fuel mode. At full load, maximum brake thermal efficiency of the engine with diesel, grapeseed biodiesel and neat grapeseed oil has increased from 32.34%, 30.28% and 25.94% to 36.04%, 33.97% and 30.95% for a maximum hydrogen energy share of 14.46%, 14.1% and 12.8% respectively. Although there is an increasing trend in Nitric Oxide emission with hydrogen induction, smoke, brake specific hydrocarbon, carbon monoxide, and carbon dioxide emissions respectively, reduces. Nitric oxide emission of Grapeseed biodiesel with maximum hydrogen share at full load is higher by 43.61% and smoke emission lower by 19.73% compared to biodiesel operation without hydrogen induction.     

The utilization of hydrogen in hydrogen/diesel dual fuel engine

A hydrogen fueled internal combustion engine has great advantages on exhaust emissions including carbon dioxide (CO₂) emission in comparison with a conventional engine fueling fossil fuel. In addition, if it is compared with a hydrogen fuel cell, the hydrogen engine has some advantages on price, power density, and required purity of hydrogen. Therefore, they expect that hydrogen will be utilized for several applications, especially for a combined heat and power (CHP) system which currently uses diesel or natural gas as a fuel.A final goal of this study is to develop combustion technologies of hydrogen in an internal combustion engine with high efficiency and clean emission. This study especially focuses on a diesel dual fuel (DDF) combustion technology. The DDF combustion technology uses two different fuels. One of them is diesel fuel, and the other one is hydrogen in this study. Because the DDF engine is not customized for hydrogen which has significant flammability, it is concerned that serious problems occur in the hydrogen DDF engine such as abnormal combustion, worse emission and thermal efficiency.In this study, a single cylinder diesel engine is used with gas injectors at an intake port to evaluate performance swung the hydrogen DDF engine with changing conditions of amount of hydrogen injected, engine speed, and engine loads. The engine experiments show that the hydrogen DDF operation could achieve higher thermal efficiency than a conventional diesel operation at relatively high engine load conditions. However, it is also shown that pre-ignition with relatively high input energy fraction of hydrogen occurred before diesel fuel injection and its ignition. Therefore, such abnormal combustion limited amount of hydrogen injected. Fire-deck temperature was measured to investigate causal relationship between fire-deck temperature and occurrence of pre-ignition with changing operative conditions of the hydrogen DDF engine.     

Dual fuel mode operation in diesel engines using renewable fuels: Rubber seed oil and coir-pith producer gas

Partial combustion of biomass in the gasifier generates producer gas that can be used as supplementary or sole fuel for internal combustion engines. Dual fuel mode operation using coir-pith derived producer gas and rubber seed oil as pilot fuel was analyzed for various producer gas–air flow ratios and at different load conditions. The engine is experimentally optimized with respect to maximum pilot fuel savings in the dual fuel mode operation. The performance and emission characteristics of the dual fuel engine are compared with that of diesel engine at different load conditions. Specific energy consumption in the dual-fuel mode of operation with oil-coir-pith operation is found to be in the higher side at all load conditions. Exhaust emission was found to be higher in the case of dual fuel mode of operation as compared to neat diesel/oil operation. Engine performance characteristics are inferior in fully renewable fueled engine operation but it suitable for stationary engine application, particularly power generation.     

Experimental investigations on a hydrogen diesel homogeneous charge compression ignition engine with exhaust gas recirculation

In this experimental study, hydrogen was inducted along with air and diesel was injected into the cylinder using a high pressure common rail system, in a single cylinder homogeneous charge compression ignition engine. An electronic controller was used to set the required injection timing of diesel for best thermal efficiency. The influences of hydrogen to diesel energy ratio, output of the engine and exhaust gas recirculation (EGR) on performance, emissions and combustion were studied in detail. An increase in the amount of hydrogen improved the thermal efficiency by retarding the combustion process. It also lowered the exhaust emissions. Large amounts of hydrogen and EGR were needed at high outputs for suppressing knock. The range of operation was brake mean effective pressures of 2–4 bar. The levels of HC and CO emitted were not significantly influenced by the amount of hydrogen that was used.     

Assessment of combustion and exhaust emissions in a common-rail diesel engine fueled with methane and hydrogen/methane mixtures under different compression ratio

This study investigates the potential usage of the methane and hydrogen enriched methane in a turbocharged common-rail direct injection diesel engine. Methane and hydrogen/methane mixtures are sent through the air intake manifold of the engine. The engine is operated at four different loads and three different compression ratios. Results are compared amongst single diesel and dual-fuel operations at different compression ratios and load conditions. Compared to diesel, dual-fuel operations mostly generate higher and advanced peak in-cylinder gas pressure, more combustion noise, late pilot injection and start of combustion, advanced combustion center, substantial variations at ignition delay and combustion duration, a significant increase in cyclic variations at low and medium loads, and earlier heat release. Hydrogen enrichment decreases evidently specific fuel consumption. Concerning emissions, compared to diesel operation, dual-fuel operations produce higher total hydrocarbon (THC) and nitrogen oxides (NO_x) but lower carbon dioxide (CO₂). Hydrogen substitutions decrease THC and CO₂ emissions of methane dual-fuel operations approximately between 9-29% and 1–32%, respectively. Smoke emission of dual-fuel operations is less than that of diesel at low and medium loads, whereas it sharply increases at high load. Knocking occurs at high compression ratio and load conditions with dual-fuel operations and dramatically increases with increasing hydrogen ratio. Decreasing the compression ratio notably reduces the combustion noise as well as some emissions, such as NO_x, CO₂ and smoke, for entire load ranges of dual-fuel and diesel operations.     

An experimental investigation of exergetic performance and emission characteristics of hydrogen supplemented biogas-diesel dual fuel engine

An experimental investigation of a conventional diesel engine with diesel, biogas and hydrogen as fuels has been carried out, while the engine is modified to operate in dual fuel mode using diesel as the pilot fuel and biogas as the main fuel respectively. In order to improve the biogas-diesel dual fuel engine performance and emission characteristics, small percentages of hydrogen supplementations, viz. 5%, 10%, 15% and 20%, in biogas were studied and the comparison was also made to that with the neat biogas-diesel dual fuel operation. Engine performance characterization has been done with exergy based approach, and major sources of irreversibilities in various engine processes are also investigated and compared for the above mentioned cases. The results show that hydrogen supplementations in biogas have lesser effect on the combustion characteristics at low load, while, at high load, the combustion patterns change significantly with higher heat release rates and peak combustion pressures. Furthermore, performance and emission characteristics are found nearly unaffected with 5% of hydrogen addition both at low and high loads. Nevertheless, further addition of hydrogen in biogas causes improvements in performance and emission characteristics of the dual fuel engine.     

Experimental investigations on the use of preheated animal fat as fuel in a compression ignition engine

The effect of fuel inlet temperature on performance, emission and combustion characteristics of a diesel engine is evaluated. A single cylinder direct injection diesel engine developing a power output of 2.8 kW at 1500 rev/min is tested using preheated animal fat as fuel. Experiments are conducted at the fuel inlet temperatures of 30, 40, 50, 60 and 70 °C. Animal fat at low temperature results in higher ignition delay and combustion duration than diesel. Preheated animal fat shows reduced ignition delay and combustion duration. Peak pressure and rate of pressure rise are found as high with animal fat at high fuel inlet temperatures. Heat release pattern shows reduced premixed combustion phase with animal fat as compared to neat diesel at normal temperature. Preheating improves the premixed combustion rate. At low temperature, animal fat results in lower smoke emissions than diesel. The maximum smoke density is K=6.5 m⁻¹ with diesel and K=3.6 m⁻¹ with animal fat at 30 °C. Preheated animal fat further reduces smoke levels at all temperatures. The smoke level is reduced up to K=1.7 m⁻¹ with preheated animal fat at the temperature of 70 °C. Hydrocarbon and carbon monoxide emissions are higher with animal fat at low temperature as compared to diesel. Fuel Preheating reduces these emissions. NO emission is found as low with animal fat at low temperature. Fuel preheating results in increased NO emission. However, the level is still lower than diesel even at high temperature (i.e. 70 °C). On the whole it is concluded that preheated animal fat can be used in diesel engines with reduced smoke, hydrocarbon and carbon monoxide emissions with no major detoriation in engine performance.     

Theoretical study of the effects of engine parameters on performance and emissions of a pilot ignited natural gas diesel engine

With the increasing concern regarding diesel vehicle emissions and the rising cost of the liquid diesel fuel as well, more conventional diesel engines internationally are pursuing the option of converting to use natural gas as a supplement for the conventional diesel fuel (dual fuel natural gas/diesel engines). The most common natural gas/diesel operating mode is referred to as the pilot ignited natural gas diesel engine (PINGDE) where most of the engine power output is provided by the gaseous fuel while a pilot amount of the liquid diesel fuel injected near the end of the compression stroke is used only as an ignition source of the gaseous fuel–air mixture. The specific engine operating mode, in comparison with conventional diesel fuel operation, suffers from low brake engine efficiency and high carbon monoxide (CO) emissions. In order to be examined the effect of increased air inlet temperature combined with increased pilot fuel quantity on performance and exhaust emissions of a PINGD engine, a theoretical investigation has been conducted by applying a comprehensive two-zone phenomenological model on a high-speed, pilot ignited, natural gas diesel engine located at the authors' laboratory. The main objectives of the present work are to record the variation of the relative impact each one of the above mentioned parameters has on performance and exhaust emissions and also to reveal the advantages and disadvantages each one of the proposed method. It becomes more necessary at high engine load conditions where the simultaneous increase of the specific engine parameters may lead to undesirable results with nitric oxide emissions.     

Effect of induction on exhaust gas recirculation and hydrogen gas in compression ignition engine with simarouba oil in dual fuel mode

Biofuels extracted from non-edible oil is sustainable and can be used as an alternative fuel for internal combustion engines. This study presents the performance, emission and combustion characteristic analysis by using simarouba oil (obtained from Simarouba seed) as an alternative fuel along with hydrogen and exhaust gas recirculation (EGR) in a compression ignition (CI) engine operating on dual fuel mode. Simarouba biofuel blend (B20) was prepared on volumetric basis by mixing simarouba oil and diesel in the proportion of 20% and 80% (v/v), respectively. Hydrogen gas was introduced at the flow rate of 2.67 kg/min, and EGR concentration was maintained at 30% of total air introduction. Performance, combustion and emission characteristics analysis were examined with biodiesel (B20), biodiesel with hydrogen substitution and biodiesel, hydrogen with EGR and were compared with neat diesel operation. Results indicate that BTE of the engine operating with biodiesel B20 was decreased when compared to neat diesel operation. However, introducing hydrogen along with B20 blend into the combustion chamber shows a slight increase in the BTE by 1%. NO_x emission was increased to 18.13% with the introduction of hydrogen than that of base fuel (diesel) operation. With the introduction of EGR, there is a significant reduction in NO_x emission due to decrease in in-cylinder temperature by 19.07%. A significant reduction in CO, CO_2, and smoke emissions were also noted with the introduction of both hydrogen and EGR. The ignition delay and combustion duration were increased with the introduction of hydrogen, EGR with biodiesel than neat diesel operation. Hence, the proposed biodiesel B20 with H₂ and EGR combination can be applied as an alternative fuel in CI engines.     

Effects of hydrogenation of fossil fuels with hydrogen and hydroxy gas on performance and emissions of internal combustion engines

Energy security is an important consideration for development of future transport fuels. Among the all gaseous fuels hydrogen or hydroxy (HHO) gas is considered to be one of the clean alternative fuels. Hydrogen is very flammable gas and storing and transporting of hydrogen gas safely is very difficult. Today, vehicles using pure hydrogen as fuel require stations with compressed or liquefied hydrogen stocks at high pressures from hydrogen production centres established with large investments.Different electrode design and different electrolytes have been tested to find the best electrode design and electrolyte for higher amount of HHO production using same electric energy. HHO is used as an additional fuel without storage tanks in the four strokes, 4-cylinder compression ignition engine and two-stroke, one-cylinder spark ignition engine without any structural changes. Later, previously developed commercially available dry cell HHO reactor used as a fuel additive to neat diesel fuel and biodiesel fuel mixtures. HHO gas is used to hydrogenate the compressed natural gas (CNG) and different amounts of HHO-CNG fuel mixtures are used in a pilot injection CI engine. Pure diesel fuel and diesel fuel + biodiesel mixtures with different volumetric flow rates are also used as pilot injection fuel in the test engine. The effects of HHO enrichment on engine performance and emissions in compression-ignition and spark-ignition engines have been examined in detail. It is found from the experiments that plate type reactor with NaOH produced more HHO gas with the same amount of catalyst and electric energy. All experimental results from Gasoline and Diesel Engines show that performance and exhaust emission values have improved with hydroxy gas addition to the fossil fuels except NO_x exhaust emissions. The maximum average improvements in terms of performance and emissions of the gasoline and the diesel engine are both graphically and numerically expressed in results and discussions. The maximum average improvements obtained for brake power, brake torque and BSFC values of the gasoline engine were 27%, 32.4% and 16.3%, respectively. Furthermore, maximum improvements in performance data obtained with the use of HHO enriched biodiesel fuel mixture in diesel engine were 8.31% for brake power, 7.1% for brake torque and 10% for BSFC.     

Low-load hydrogen-diesel dual-fuel engine operation – A combustion efficiency improvement approach

Hydrogen-diesel dual-fuel operation can provide significant benefits to the performance and carbon-based emissions formation of compression-ignition engines. The wide flammability range of hydrogen allows engine operation at extremely low equivalence ratios while its high diffusivity and flame speed promote wide range combustion inside the cylinder. Nonetheless, despite the excellent properties of hydrogen for internal combustion, unburned hydrogen emissions and poor combustion efficiency have been previously observed at low-load conditions of compression ignition engines.The focus of the present study is to assess the effects of different engine operation and diesel injection parameters on the combustion efficiency of a heavy-duty dual-fuel engine while observing their interactions with the brake thermal efficiency (BTE) and emissions formation of the engine. In an attempt to reduce the unburned hydrogen rates at the exhaust of the engine, exhaust gas recirculation (EGR) and different diesel injection strategies were implemented. Statistical methods were applied in this study to reduce the experimental time.The results show a strong connection between unburned hydrogen rates, combustion and brake thermal efficiencies with the EGR rate. Higher EGR rates increase the intake charge temperature and provide improved hydrogen combustion and fuel economy. Operation of the dual-fuel engine at low-load with high EGR rate and slightly advanced main diesel injection can deliver simultaneous benefits to most of the harmful emissions and the BTE of the engine. Despite the efforts to achieve optimal engine operation at low loads, the combustion efficiency for most of the tested cases was in the range of 90%. Thus, increased hydrogen rates should be avoided as the benefits of the dual-fuel operation are weak at low-load conditions.     

Effect of methanol fumigation on performance and emission characteristics in a waste cooking oil-fuelled single cylinder CI engine

Use of bio-oils in diesel engines results in increased NOx and smoke and reduced brake thermal efficiency. Dual-fuel engines can use a wide range of fuels mainly alcohols and yet operate with high thermal efficiency and simultaneous reduction of NO and smoke emissions. The present study aims to explore the effect of methanol–waste cooking oil (WCO) dual-fuel mode on performance and emission characteristics in a single cylinder Compression ignition (CI) engine producing 3.7 kW at 1,500 rpm. WCO was injected in the conventional injection system, replacing diesel as pilot fuel. Methanol was fumigated along with intake air using a variable jet carburetor, which was installed in the inlet manifold. The methanol was fumigated, and the energy share was varied for each load till the knock limit. Performance parameters like brake thermal efficiency (BTE) and emission parameters like HC, CO, NO, and smoke emissions were tested for various energy shares of methanol with WCO as a pilot fuel. The results show that an increase in methanol fumigation reduced BTE at lower loads. At 75% and 100% load conditions, BTE was higher with methanol addition. The maximum BTE was observed for 38% methanol share, which is about 11% higher, compared to WCO at 100% load condition. Methanol fumigation aided in the simultaneous reduction of NO and smoke emission, and the maximum reduction was occurred with 51% methanol share at 100% load condition. HC and CO emissions were higher at all load conditions with methanol fumigation.     

Combustion,performance and emission analyses of a CI engine operating with renewable diesel fuels (HVO/FARNESANE) under dual-fuel mode through hydrogen port injection

The use of hydrogen in internal combustion engines is pointed out as an alternative to reduce greenhouse gas emissions. In applications that require high levels of torque and low engine speeds, compression ignition (CI) engines are more appropriate. However, because of the high auto-ignition temperature of hydrogen, its use in these engine types is more suitable when the dual-fuel concept is applied. This study comprehensively investigates, through experimental techniques, the use of hydrogen port-injection in a four-stroke single-cylinder CI engine operating with the renewable diesel-like fuels hydrotreated vegetable oil (HVO) and farnesane, in comparison to fossil diesel dual-fuel operation. In this sense, the present work aims to fill a gap in the literature by performing a novel analysis of dual-fuel operation with hydrogen, considering different substitution fractions, and using groundbreaking biofuels, such as HVO and farnesane. The results showed that in-cylinder pressure and temperature were increased with H₂ enrichment for every pilot fuel, but green diesel fuels presented lower values than those for diesel operation. Furthermore, hydrogen port injection slightly delayed the start of combustion and increased the ignition delay, but a reduction in both premixed and diffusion combustion duration was observed. Reductions in PM, CO, and CO₂ emissions were reported during H₂ addition for every pilot fuel, while increased NO_x was observed. Despite this increase, both HVO and farnesane decreased the emissions of this pollutant in single and dual-fuel operations, compared with fossil diesel. In addition, both renewable diesel fuels presented higher BTE than diesel for every studied H₂ mass flow.     

Combustion,performance and emissions of a diesel engine with H2, CH4 and H2–CH4 addition

Experiments were conducted to investigate the combustion and emission characteristics of a diesel engine with addition of hydrogen or methane for dual-fuel operation, and mixtures of hydrogen–methane for tri-fuel operation. The in-cylinder pressure and heat release rate change slightly at low to medium loads but increase dramatically at high load owing to the high combustion temperature and high quantity of pilot diesel fuel which contribute to better combustion of the gaseous fuels. The performance of the engine with tri-fuel operation at 30% load improves with the increase of hydrogen fraction in methane and is always higher than that with dual-fuel operations. Compared with ULSD–CH₄ operation, hydrogen addition in methane contributes to a reduction of CO/CO₂/HC emissions without penalty on NO_x emission. Dual-fuel and tri-fuel operations suppress particle emission to the similar extent. All the gaseous fuels reduce the geometry mean diameter and total number concentration of diesel particulate. Tri-fuel operation with 30% hydrogen addition in methane is observed to be the best fuel in reducing particulate and NO_x emissions at 70 and 90% loads.