• Energy Research

Over the past few years, fuel prices have increased dramatically, and emissions regulations have become stricter in maritime applications. In order to take these factors into consideration, improvements in fuel consumption have become a mandatory factor and a main task of research and development departments in this area. Internal combustion engines (ICEs) can exploit only about 15–40% of chemical energy to produce work effectively, while most of the fuel energy is wasted through exhaust gases and coolant. Although there is a significant amount of wasted energy in thermal processes, the quality of that energy is low owing to its low temperature and provides limited potential for power generation consequently. Waste heat recovery (WHR) systems take advantage of the available waste heat for producing power by utilizing heat energy lost to the surroundings at no additional fuel costs. Among all available waste heat sources in the engine, exhaust gas is the most potent candidate for WHR due to its high level of exergy. Regarding WHR technologies, the well-known Rankine cycles are considered the most promising candidate for improving ICE thermal efficiency. This study is carried out for a six-cylinder marine diesel engine model operating with a WHR organic Rankine cycle (ORC) model that utilizes engine exhaust energy as input. Using expander inlet conditions in the ORC model, preliminary turbine design characteristics are calculated. For this mean-line model, a MATLAB code has been developed. In off-design expander analysis, performance maps are created for different speed and pressure ratios. Results are produced by integrating the polynomial correlations between all of these parameters into the ORC model. ORC efficiency varies in design and off-design conditions which are due to changes in expander input conditions and, consequently, net power output. In this study, ORC efficiency varies from a minimum of 6% to a maximum of 12.7%. ORC efficiency performance is also affected by certain variables such as the coolant flow rate, heat exchanger’s performance etc. It is calculated that with the increase of coolant flow rate, ORC efficiency increases due to the higher turbine work output that is made possible, and the condensing pressure decreases. It is calculated that ORC can improve engine Brake Specific Fuel Consumption (BSFC) from a minimum of 2.9% to a maximum of 5.1%, corresponding to different engine operating points. Thus, decreasing overall fuel consumption shows a positive effect on engine performance. It can also increase engine power output by up to 5.42% if so required for applications where this may be deemed necessary and where an appropriate mechanical connection is made between the engine shaft and the expander shaft. The ORC analysis uses a bespoke expander design methodology and couples it to an ORC design architecture method to provide an important methodology for high-efficiency marine diesel engine systems that can extend well beyond the marine sector and into the broader ORC WHR field and are applicable to many industries (as detailed in the Introduction section of this paper).

The battery thermal management system (BTMS) for lithium-ion batteries can provide proper operation conditions by implementing metal cold plates containing channels on both sides of the battery cell, making it a more effective cooling system. The efficient design of channels can improve thermal performance without any excessive energy consumption. In addition, utilizing phase change material (PCM) as a passive cooling system enhances BTMS performance, which led to a hybrid cooling system. In this study, a novel design of a microchannel distribution path where each microchannel branched into two channels 40 mm before the outlet port to increase thermal contact between the battery cell and microchannels is proposed. In addition, a hybrid cooling system integrated with PCM in the critical zone of the battery cell is designed. Numerical investigation was performed under a 5C discharge rate, three environmental conditions, and a specific range of inlet velocity (0.1 m/s to 1 m/s). Results revealed that a branched microchannel can effectively improve thermal contact between the battery cell and microchannel in a hot area of the battery cell around the outlet port of channels. The designed cooling system reduces the maximum temperature of the battery cell by 2.43 °C, while temperature difference reduces by 5.22 °C compared to the straight microchannel. Furthermore, adding PCM led to more uniform temperature distribution inside battery cell without extra energy consumption.

Abstract Hydrogen, oxygen, and their combinations as effective species in the production of radical OH, which plays an effective role in the HCCI combustion enhancement, are considered to study their effect on combustion characteristics and resolving the challenges facing natural gas HCCI engines numerically. There are five items were considered for adding oxygen, hydrogen and their compounds, including 1%, 2%,3%, 4% and 5% of the fuel mixture for hydrogen, 10%, 20%, 30%, 40% and 50% for the extra oxygen in oxidizer and add up half of each respectively, including 0.5% H2 + 5%O2, 1% H2 + 10%O2, 1.5% H2 + 15%O2, 2% H2 + 20%O2, and 2.5% H2 + 25%O2. Adding hydrogen to some extent improves the engine efficiency, lowers combustion duration, and brings the engine cycle closer to the ideal Otto cycle and reduces CO and UHC emissions, but it can only increase engine operating range by as much as 4.2% at low load, increases NO emission, and increases the combustion noise. Hydrogen addition results in faster methane combustion, shortens the fuel combustion duration and increases the OH radical concentration. Up to 30%, added oxygen can extend the engine working range up to 48% at low loads, making the engine run smoother and shortening the combustion duration, although IMEP and efficiency decrease, CO and UHC emissions increase. By using hydrogen and oxygen compounds obtained their both benefits simultaneously, the engine operating range expands by 40.19% at low loads, the emissions would be less than the Euro 6 standard limitation and the maximum difference in efficiency is only 2.38% less than hydrogen addition. By adding these additives, ignition delay decreases and SOC advances. Using hydrogen and oxygen to improve engine performance at low loads is an appropriate and affordable solution, which does not cost much.

Abstract In CNG/Diesel reactivity controlled compression ignition (RCCI) engines, because of low reactivity fuel (natural gas) spread of flame in combustion chamber suffers process of combustion and also there is more unburned hydrocarbon emission in this type of engine due to flame spread, free-combustion points, penetrating gas into rings and cavities. Using hydrogen as an additive can improve combustion process, improve engine performance and reduce emissions. By this research, a computational fluid dynamic modeling in coupling with Chemkin solver has been used to investigate the effects of hydrogen as an additive in RCCI CNG/Diesel internal combustion engine. Numerical results have been validated by a single cylinder Ricardo E6/MS engine that equipped by a standard Comet MK.V pre-chamber. Three different concentrations (10%, 20% and 30% in volume) of hydrogen have been studied by this modeling. Specification of Ricardo engine have been used for CFD modeling from IVC to EVO as a close system modeling. There is a good flow structure with good swirling flow before combustion that makes fuel more suitable for starting combustion. HRR diagrams show a delay in combustion by adding hydrogen in natural gas and air. IMEP, gross work and IFCE improved by 5.01%, 5.01% and 5.04% in concentration of 30% hydrogen, respectively. There are a descend in mass fraction of UHC and CO in different hydrogen concentration that 30% H2 addition in fuel makes the amount of UHC and CO lower by 29.8% and 35.5%, correspondingly. This is in a condition that in-cylinder temperature rises about 2.9% by 30% of hydrogen adding. NOx emissions has been risen during adding H2 because of increasing temperature, this increment is about 23.1% at 30% hydrogen that can be an undesired effect of using H2 as an additive. In general, the simultaneous use of Pre-chamber and hydrogen has been able to reduce the amount of CO and UHC, but the amount of nitrogen oxide has been increased.

Abstract Reactivity controlled compression ignition engines have been proven to have better performance comparing with other methods of low temperature combustion strategies. Using various fuels can have different outputs according to the chemical products and reactions as well as heating values. In this study, a numerical model beside experimental data as validation is used to investigate the effects of using additive on combustion characteristics of natural gas/dimethyl-ether and natural-gas/diesel Reactivity controlled compression ignition engines. Hydrogen is used as additive with 3, 6 and 9 percentage of heating value in the fuel mixture. Results show higher indicated mean effective pressure in all cases of using diesel as high reactivity fuel. In addition, investigation on the combustion characteristics shows that natural gas/diesel cases have advanced start of combustion and combustion phasing, while burn duration in natural gas/dimethyl-ether cases is higher than natural gas/diesel cases. By adding hydrogen species, it is seen that hydrogen has more effect on the start of combustion of natural gas/dimethyl-ether case where adding 9% hydrogen, advanced the start of combustion about 2 crank angle degree while this amount for natural gas/diesel case is about 0.3. In all cases of using diesel as high reactivity fuel, temperature is higher than dimethyl-ether used cases, which causes to produce more nitrogen oxides; for example, in 9% hydrogen addition, natural gas/diesel mode produced 0.54 g/kW/h nitrogen oxide more than natural gas/dimethyl-ether mode. Based on achieved results, carbon monoxide emission in natural gas/diesel mode is lower than 2 g/kW/h for all cases where this emission is higher than 8 g/kW/h in each case of natural gas/dimethyl-ether. This condition was also occurred for unburned hydrocarbons emissions, where this emission is higher than 11 g/kW/h for natural gas/dimethyl-ether fueling case while it is lower than 2 g/kW/h for natural gas/diesel mode. Quantitatively comparison shows that hydrogen addition is more effective on natural gas/dimethyl-ether reactivity controlled compression ignition mode. According to dimethyl-ether breaking up process, start of injection provides a time to decomposition of dimethyl-ether to its products, especially Methane. Based on numerical results, more than 10% of dimethyl-ether is broken up before start of combustion that represented importance of start of injection in natural gas/dimethyl-ether case.

Abstract Today’s researchers have made concerted efforts to benefit from biodiesel and to achieve better combustion due to its higher cetane number in comparison to that of diesel. The major drawback of utilizing biodiesel-diesel blend is the corresponding increase in the NOx emission, which can be solved using water. However, water results in higher HC and CO emissions that can be handled by the addition of metal-based nano-particles such as cerium oxide (CeO2). In this study, 36 different cases of these input parameters (different values of biodiesel, water, and nano-particles) have been examined experimentally, and the results are used to train an artificial neural network (ANN) model to produce 8866 data. Then, these data were utilized to find the maximum brake thermal efficiency while the value of output emissions and brake specification fuel consumption are minimum. In this regard, a new parameter called performance evaluation of diesel engine (PEDE) was introduced to decrease the number of output parameters into one. However, the results of sensitivity analysis on the PEDE indicated that the share of output parameters on this newly defined PEDE are not the same, and it demands modifications. Therefore, the exponents of each output parameter were modified by the application of sensitivity analysis. Finally, a modified PEDE that can predict the performance of diesel engines properly was introduced, and the optimum values were presented. Results indicated that the best performance occurs when the amount of cerium oxide nano-particles is 80 ppm, while the shares of biodiesel and water are 6 percent.