| 1. |
- Alemahdi, Nika, et al.
(författare)
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Development of an empirical test method to quantify the ɸ-sensitivity of liquid fuels
- 2022
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Ingår i: Energy Conversion and Management. - : Elsevier BV. - 0196-8904. ; 254
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Tidskriftsartikel (refereegranskat)abstract
- Several researchers are investigating strategies to lower the emissions and increase the efficiency of combustion engines to reduce the negative impact on the environment and the climate from transportation. The low-temperature combustion (LTC) concept is the basis for some of these high-efficiency, low-emission combustion technologies. To maximize the combustion controllability of engines based on the LTC concept, the combustion behavior of fuel both at different equivalence ratios (ɸ) and under ɸ sweeps must be understood and planned precisely. The ɸ-sensitivity of a fuel explains its behavior at different engine loads or stratification levels. In this study, a new test method for empirically evaluating ɸ-sensitivity using a Cooperative Fuel Research (CFR) engine is proposed and the validity of the method is investigated. A modified CFR engine for homogeneous-charge compression ignition (HCCI) combustion is used to investigate the compression ratio (CR) sensitivity of different toluene–ethanol reference fuels (TERFs) in a research octane number (RON) range of 63–105. This study suggests a method to quantify the ɸ-sensitivity of different fuels and blends by measuring the compression ratio required to keep the CA50 constant while varying ɸ. It shows that the fuel composition greatly affects the fuel ɸ-sensitivity even for different blends with the same RON. The results also indicate that the coexistence of ethanol and toluene in a blend can generate the highest ɸ-sensitivity of the blend compared to other blends with the same RON. Fuel composition has a strong effect on emissions. The simultaneous effect of fuel composition and ɸ variation on the emission and stability parameters is nonlinear.
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| 2. |
- Alemahdi, Nika
(författare)
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Enhanced mesophilic bio-hydrogen production of raw rice straw and activated sewage sludge by co-digestion
- 2015
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 40:46, s. 16033-16044
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Tidskriftsartikel (refereegranskat)abstract
- In this study, batch biohydrogen production by co-digestion of raw rice straw and activated sewage sludge was investigated with different inoculum heat treatment, pH, S/X ratio (based on VS) and substrate sizes under mesophilic condition. In order to achieve a high bio-hydrogen yield and methanogens activity inhibition, heat treatment of inoculum was optimized at different exposure times (30, 45 & 60 min) and temperature ranges (80, 90 and 100 °C) prior to dark fermentation process. Collected data was analysed using response surface methodology (RSM). The heat treatment of inoculum at 100 °C for 60 min produced the highest bio-hydrogen yield of 14.22 NmL H2/g VS at concentration of 70.97% and Production of 0.073 NmL CH4/g VS at 0.17% concentration in total produced biogas. The raw rice straw was also co-digested with heat-treated inoculum at different ratios of volatile solids (2:1, 4:1 and 6:1) and initial pH (4, 4.75 and 5.5) as numerical variables and 4 categories of substrate size ((250–500 μm], (500 μm-2mm], (2–20 mm), [20–30 mm]). The highest bio-hydrogen yield of 14.70 NmL/g VS was recognized at the optimum initial pH of 5.01 and S/X ratio of 4.54:1 using 2–20 mm rice straw.
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| 3. |
- Alemahdi, Nika, et al.
(författare)
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The effect of 2-ethyl-hexyl nitrate on HCCI combustion properties to compensate ethanol addition to gasoline
- 2020
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Ingår i: Fuel. - : Elsevier BV. - 1873-7153 .- 0016-2361. ; 270
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Tidskriftsartikel (refereegranskat)abstract
- Stable HCCI combustion requires a proper level of fuel reactivity. This study shows that adding ethanol as a renewable fraction to low octane gasoline decreases the reactivity of the gasoline, while adding 2-ethyl hexyl nitrate (2-EHN) can enhance the reactivity of the blend and counter the effect of ethanol.The experimental apparatus consisted of a modified CFR engine for HCCI combustion equipped with two port fuel injectors and an intake air heater. Gasoline blended with ethanol (10% v/v) was used as the base fuel. Different percentages of 2-EHN (0.25%, 0.50%, 1%, and 2.5%) were added to the base fuel as an ignition improver. The blends were tested at operating points defined for HCCI number at two different engine speeds (600 and 900 rpm) and three different intake temperatures (50, 100, and 150 °C) to investigate the effect of 2-EHN on the auto-ignition behavior of the fuel.Combustion, emissions, and performance parameters of HCCI combustion of the blends were measured. The presence of 2-EHN in the blends improved the auto-ignitability of the blends in a nonlinear manner. It was also found that 0.25% of 2-EHN can compensate for the effect of ethanol on the required compression ratio and remove the quenching effect of ethanol on low temperature heat release. The results show that for the same fuel, a higher compression ratio is needed to maintain the combustion phasing constant at a higher engine speed.
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| 4. |
- Alemahdi, Nika, et al.
(författare)
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Understanding the effect of Intake temperature on the ϕ-sensitivity of toluene-ethanol reference fuels and neat ethanol
- 2023
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Ingår i: International Journal of Engine Research. - : SAGE Publications. - 1468-0874 .- 2041-3149. ; 24:7, s. 2908-2920
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Tidskriftsartikel (refereegranskat)abstract
- The low-temperature combustion (LTC) is an attractive concept that enables the modem combustion engines to move toward sustainability mainly by increasing the efficiency and decreasing the emissions. The modern combustion engines which are working based on the LTC concept have specific fuel requirements. Fuel ϕ-sensitivity is a key factor to be considered for tailoring fuels for these engines. Fuel with a high ϕ-sensitivity are more responsive to thermal or fuel stratifications; the auto-ignition properties of different air-fuel mixtures of these fuels, with different equivalence ratio (ϕ), are more diverse. This diversity provide a smoother heat release rate in stratified condition. In this study 11 different toluene–ethanol reference fuels (TERFs) in three research octane number (RON) groups of 63, 84, and 105 together with neat ethanol are evaluated. The Lund ϕ-sensitivity method is used to evaluate these fuels in a cooperative fuel research (CFR) engine. The effect of variation of intake temperature on pressure sensitivity of fuel at a constant combustion phasing is evaluated. This evaluation is performed at two intake temperature of 373 and 423 K, and the results are compared with the outcome of the Lund ϕ-sensitivity number with the intake temperature of 323 K. This study shows that the CR sensitivity response of different blends to the intake charge temperature variation depends on the fuel composition. Accumulated low temperature heat release and latent heat of vaporization. It proves that the fuel ϕ-sensitivity will vary under different thermodynamic conditions. There was a clear link between the accumulated heat released during the early reaction and CR sensitivity of the blends at different intake temperature of 373 and 423 K but the link with the latent heat of vaporization (HoV) found to be inexplicit.
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| 5. |
- Alemahdi, Nika
(författare)
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ɸ‑sensitivity : A step forward in future fuels evaluation
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Internal combustion engine is a developed and established technology whichcontributes largely to the transportation of goods and people. In one hand, theburning of fossil fuels is the main reason for the combustion engines to beconsidered unsustainable while on the other hand, the combustion behaviour ofrenewable fuels is not fully understood yet. This lack of knowledge is morepronounced when it comes to the combustion behaviour of renewable fuels inadvanced combustion engine concepts.In this PhD study a new empirical methods of fuel testing have been developed to quantify the equivalence ratio‑sensitivity of different liquid fuels. Equivalence ratio (ɸ) is the ratio of the actual fuel/air ratio to the stoichiometric fuel/air ratio.ɸ‑sensitivity is a decisive fuel property when it comes to the modern lowtemperature combustion technologies. The developed method in this study,characterize the ɸ‑sensitivity property of liquid fuels. ɸ‑sensitivity is fundamentally the sensitivity of auto‑ignition temperature or ignition delay to the variation of fuel equivalence ratio in the combustion. This property is important to understand since it separates different fuels impact on efficiency and emissions for modern engines where current fuel characterization methods (octane rating and cetane number) are indifferent. Therefore, ɸ‑sensitivity is needed to be understood for the development of renewable fuels in both conventional and advanced combustion engines. In this study a special test engine which is designed to be used for gasoline octane rating is the experimental apparatus. The Cooperative Fuel Research (CFR) engine is how this engine is called. In this engine, the height of cylinder head is adjustable to provide different Compression Ratio (CR). The variable CR of this engine makes it versatile for testing different fuels having different physical and chemicalproperties.Since the aim of this study was to develop an empirical ɸ‑sensitivity test method,different surrogate gasoline has been designed to cover a wide range of Research Octane Number (RON) values (≈105‑63). Surrogate fuels are single‑component fuels, binary blends, and multi‑component blends that are prepared in a way that emulates the desirable physical or chemical property of a more complex hydrocarbon like gasoline. In this study four components are used to prepare desirable surrogate fuels. These components are toluene, ethanol, iso‑octane, and n‑heptane. After method development step, four different alcohols were evaluated using the method. Due to the property similarity of iso‑butanol and n‑butanol to conventional gasoline, these two alcohols have been evaluated. Furthermore, blends of iso-butanol with RON (87) surrogate gasoline were evaluated. The result of this study shows that the developed test method (Lund ɸ‑sensitivity number) is an appropriate platform to evaluate and tailor fuels with a preferable ɸ‑sensitivity at a desirable octane number. Liquid fuels from renewable to conventional, to blends of renewable and conventional can be evaluated using Lund ɸ‑sensitivity method.Using this method provides required knowledge for application of different renewable fuels in internal combustion engines.
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| 6. |
- Alemahdi, Nika, et al.
(författare)
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Φ-Sensitivity Evaluation of n-Butanol and Iso-Butanol Blends with Surrogate Gasoline
- 2023
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Ingår i: SAE Tecnical papers. - 0148-7191.
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Konferensbidrag (refereegranskat)abstract
- Using renewable fuels is a reliable approach for decarbonization of combustion engines. iso-Butanol and n-butanol are known as longer chain alcohols and have the potential of being used as gasoline substitute or a renewable fraction of gasoline. The combustion behavior of renewable fuels in modern combustion engines and advanced combustion concepts is not well understood yet. Low-temperature combustion (LTC) is a concept that is a basis for some of the low emissions-high efficiency combustion technologies. Fuel Φ-sensitivity is known as a key factor to be considered for tailoring fuels for these engines. The Lund Φ-sensitivity method is an empirical test method for evaluation of the Φ-sensitivity of liquid fuels and evaluate fuel behavior in thermal. iso-Butanol and n-butanol are two alcohols which like other alcohol exhibit nonlinear behavior when blended with (surrogate) gasoline in terms of RON and MON. In this study, first the Lund Φ-sensitivity numbers of iso-butanol and n-butanol at CA50≈3°CA after TDC is measured. CA50 is the rank angle degree at which 50% of total accumulated heat is released. Then, the Lund Φ-sensitivity number of iso-butanol at two later combustion phasing of CA50≈8 & 6 °CA after TDC is evaluated. Finally, the Lund Φ-sensitivity number of volumetric blends of iso-butanol and surrogate gasoline (RON≈87) were measured. The results show the Φ-sensitivity of iso-butanol is lower than n-butanol which means the combustion behavior of iso-butanol is less sensitive to thermal and fuel stratification. The nonlinear behavior of Lund Φ-sensitivity number of iso-butanol blends with surrogate gasoline is observed. As expected, the later combustion phasing lowers the Lund Φ-sensitivity number of the tested fuel and increases the experimental range successfully.
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| 7. |
- Garcia, Antonio, et al.
(författare)
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Development of a fast-virtual CFR engine model and its use on autoignition studies
- 2021
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Ingår i: Fuel Processing Technology. - : Elsevier BV. - 0378-3820. ; 224
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Tidskriftsartikel (refereegranskat)abstract
- Homogenous charge compression ignition engines have been studied as an alternative to the conventional diesel combustion to attain high efficiency with ultra-low NOx and soot emissions for a wide variety of fuels. However, its usage in real applications has been restricted due to the difficulties regarding combustion control and operating range extension. The modification of the fuel characteristics may be a pathway to solve the previous hurdles. Therefore, this research presents a relevant methodology to assess the fuel response to HCCI boundary conditions based on 0-D and 1-D modelling for detailed chemistry solution and state conditions definition, respectively. The results suggest that the methodology can predict the early stages of the fuel oxidation with good accuracy. For the objective of predicting the start of combustion, the best results are obtained using tabulated chemistry when investigating fuels that have pre reactions and a low temperature heat release. As the oxidation process progresses, the deviation of the pressure-temperature trajectory from non-reactive to reactive conditions after the low temperature heat release decreases the predictive capability to some extent. Nonetheless, the methodology outcomes are still valid as a qualitative metric for reactivity determination as well as the intermediate and high temperature ignition delay.
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| 8. |
- Malmborg, Vilhelm, et al.
(författare)
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Potential air-quality improvements with future energy carriers in transportation
- 2022
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- AimOur aim is to provide a-priori information on air-quality implications of potential future energy carriers in transportation relevant for sustainability, life cycle and health-impact assessments.MethodologyInformation on air- and climate-pollutant formation from energy carriers is collected in detailed laboratory assessments on heavy-duty combustion engines as well as on non-tailpipe emissions. We target energy efficiency, characteristics of primary pollutants, characteristics after atmospheric transformation (ageing), and toxicological relevance.Key results/conclusions Emissions from renewable energy carriers for heavy-duty transportation that exist on the markets today (alcohols, FAME, HVO) have been reported by our groups. The results show a need for new future energy carriers with inherent low pollution formation potential and a production potential for electrofuels (e-fuels). Non-tailpipe emissions may increase for certain energy carriers. Knowledge on health and climate implications of different emissions mitigating strategies is necessary to ensure a sustainable path forward for the transport sector.
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| 9. |
- Olson, André L., et al.
(författare)
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Experimental Investigation of Glycerol Derivatives as Low-Concentration Additives for Diesel Fuel
- 2023
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Ingår i: SAE Technical Papers.
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Konferensbidrag (refereegranskat)abstract
- The worldwide adoption of renewable energy mandates, together with the widespread utilization of biofuels has created a sharp increase in the production of biodiesel (fatty acid alkyl esters). As a consequence, the production of glycerol, the main by-product of the transesterification of fatty acids, has increased accordingly, which has led to an oversupply of that compound on the markets. Therefore, in order to increase the sustainability of the biodiesel industry, alternative uses for glycerol need to be explored and the production of fuel additives is a good example of the so-called glycerol valorization. The goal of this study is therefore to evaluate the suitability of a number of glycerol-derived compounds as diesel fuel additives. Moreover, this work concerns the assessment of low-concentration blends of those glycerol derivatives with diesel fuel, which are more likely to conform to the existing fuel standards and be used in unmodified engines. The various blends described in this article were tested on a heavy-duty diesel engine converted to single-cylinder operation. The overall behavior and the impact of the fuel blends on the engine's combustion, performance, and emissions were investigated. The results showed that the additives caused a modest decrease in engine-out soot concentrations along with slightly reduced hydrocarbon and carbon monoxide emissions. In addition, the blends appeared to have a positive impact on the soot-NOx trade-off. Finally, as expected, volumetric fuel consumption was slightly increased with the oxygenated blends, due to their lower heating values. In conclusion, even though the use of the glycerol derivatives in low concentrations did not produce dramatic outcomes, the results showed that they can nevertheless be used as a means to decrease fossil fuel usage in the transportation sector.
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