Reactivity Controlled Compression Ignition Research Articles

Use of waste plastic oil as a fuel in reactivity-controlled compression ignition engines: a bibliometric investigation from 2017–23

Abstract Waste plastic oil, generated through the pyrolysis of plastic without oxygen, known as plastic-to-fuel conversion, stands as a promising alternative fuel. This research employs bibliometric analysis, a quantitative method, to comprehensively assess publications in the domain of waste plastic oil integration within reactivity-controlled compression ignition engines. Utilizing Scopus as the primary repository post-2017, the study categorizes information into pivotal aspects, including influential journals, countries, authors, affiliations, document types, thematic areas, sponsors and keywords. The analysis reveals significant contributions from diverse nations, prominently India, China, Turkey and Malaysia. Noteworthy is the prevalence of Energy, Engineering and Chemical Engineering as thematic focal points, with the journal Fuel leading the count followed by the journal Energy emerging as a prominent conduit. Institutional contributions are prolific, led by Gandhi Institute of Technology and Management University and Vellore Institute of Technology. Renowned authors ‘Gugulothu S.K’ and ‘He Z’ play a pivotal role in shaping the discourse. The National Natural Science Foundation of China stands out as a primary patron. This bibliometric analysis provides a structured understanding of waste plastic oil integration in reactivity-controlled compression ignition engines, laying the groundwork for future research avenues. The study identifies potential research platforms beyond Scopus, including Web of Science, CrossRef, Science Direct and Google Scholar, as valuable repositories for further exploration. Moreover, after careful observation of the research articles published by the top 10 authors as found in the study, it was found that the authors share a few common characteristics that helped them in advancing the understanding and application of waste plastic oil in reactivity-controlled compression ignition engines. These are also summarized in the present study with supporting data.

Dimethyl Ether Biogas Reactivity-Controlled Compression Ignition for Sustainable Power Generation with Low Nitrogen Oxide Emissions

<div>Biogas (60% methane–40% CO<sub>2</sub> approximately) can be used in the reactivity-controlled compression ignition (RCCI) mode along with a high-reactivity fuel (HRF). In this work dimethyl ether (DME) that can also be produced from renewable sources was used as the HRF as a move toward sustainable power generation. The two-cylinder turbocharged diesel engine modified to work in the DME–biogas RCCI (DMB-RCCI) mode was studied under different proportions of methane (45–95%) in biogas since the quality of this fuel can vary depending on the feedstock and production method. Only a narrow range of biogas to DME ratios could be tolerated in this mode at each output without misfire or knock. Detailed experiments were conducted at brake mean effective pressures (BMEPs) of 3 and 5 bar at a speed of 1500 rpm and comparisons were made with the diesel–biogas dual-fuel and diesel–biogas RCCI modes under similar methane flow rates while the proportion of CO<sub>2</sub> was varied. The DMB-RCCI mode exhibited superior brake thermal efficiency (25.3% as against 22% and 31.5% as against 29% at the BMEPs of 3 and 5 bar) as compared to the other modes and was not sensitive to the concentration of methane. The NOx and soot emissions were also negligible and the lowest CH<sub>4</sub> emission levels were also attained. The cyclic fluctuations in IMEP were lower than 5% in this mode. Thus, DME can be used along with biogas to enhance its reactivity for sustainable power generation in the RCCI mode.</div>

Data-Based In-Cylinder Pressure Model with Cyclic Variations for Combustion Control: An RCCI Engine Application

Cylinder-pressure-based control is a key enabler for advanced pre-mixed combustion concepts. In addition to guaranteeing robust and safe operation, it allows for cylinder pressure and heat release shaping. This requires fast control-oriented combustion models. Over the years, mean-value models have been proposed that can predict combustion metrics (e.g., gross indicated mean effective pressure (IMEPg), or the crank angle where 50% of the total heat is released (CA50)) or models that predict the full in-cylinder pressure. However, these models are not able to capture cycle-to-cycle variations. The inclusion of the cycle-to-cycle variations is important in the control design for combustion concepts, like reactivity-controlled compression ignition, that can suffer from large cycle-to-cycle variations. In this study, the in-cylinder pressure and cycle-to-cycle variations are modelled using a data-based approach. The in-cylinder conditions and fuel settings are the inputs to the model. The model combines principal component decomposition and Gaussian process regression. A detailed study is performed on the effects of the different hyperparameters and kernel choices. The approach is applicable to any combustion concept, but is most valuable for advance combustion concepts with large cycle-to-cycle variation. The potential of the proposed approach is successfully demonstrated for a reactivity-controlled compression ignition engine running on diesel and E85. The average prediction error of the mean in-cylinder pressure over a complete combustion cycle is 0.051 bar and of the corresponding mean cycle-to-cycle variation is 0.24 bar2. This principal-component-decomposition-based approach is an important step towards in-cylinder pressure shaping. The use of Gaussian process regression provides important information on cycle-to-cycle variation and provides next-cycle control information on safety and performance criteria.

Study on the Effect of Two-Stage Injection Strategy for Coal-to-Liquid/Gasoline Reactivity-Controlled Compression Ignition Combustion Mode.

An experimental study was carried out on a modified single-cylinder dual-fuel engine in reactivity-controlled compression ignition (RCCI) mode using pilot fuels with different physicochemical properties, and the effects of the pilot fuels and the two-stage injection strategy on the combustion and emission characteristics of the RCCI mode were explored. The results show that when coal-to-liquid (CTL) is used with a high cetane number as the pilot fuel, the reactivity stratification of the fuel-air mixture is more pronounced. With the advancement of pilot injection timing (SOI1), the heat release rate (HRR) of the CTL/gasoline mode gradually changes from a bimodal pattern to a unimodal pattern. Among them, the bimodal HRR includes CTL premixed combustion and gasoline flame propagation, as well as CTL diffused combustion and gasoline multipoint spontaneous combustion, while the unimodal HRR represents CTL premixed combustion and gasoline multipoint spontaneous combustion. However, the HRR of the fossil diesel/gasoline RCCI combustion mode always exhibits a unimodal form. With the advancement of the main injection timing (SOI2), the gravity center of heat release (CA50) is more advanced when using CTL as the pilot fuel due to the short ignition delay. Overall, compared to fossil diesel, using CTL as the pilot fuel is conducive to controlling the pressure rise rate, which expands the operating range of the RCCI combustion mode. Besides, for both pilot fuels of CTL and fossil diesel, the advancement of SOI1 lowers particle emissions, and the advancement of SOI2 reduces NOx emissions, while the two-stage injection achieves higher indicated thermal efficiency.

Integrated 1D Simulation of Aftertreatment System and Chemistry-Based Multizone RCCI Combustion for Optimal Performance with Methane Oxidation Catalyst

This paper presents a comprehensive investigation into the design of a methane oxidation catalyst aftertreatment system specifically tailored for the Wärtsilä W31DF natural gas engine which has been converted to a reactivity-controlled compression ignition NG/Diesel engine. A GT-Power model was coupled with a predictive physical base chemical kinetic multizone model (MZM) as a combustion object. In this MZM simulation, a set of 54 species and 269 reactions as chemical kinetic mechanism were used for modelling combustion and emissions. Aftertreatment simulations were conducted using a 1D air-path model in the same GT-Power model, integrated with a chemical kinetic model featuring 15 catalytic reactions, based on activation energy and species concentrations from combustion outputs. The latter offered detailed exhaust composition and exhaust thermodynamic data under specific operating conditions, effectively capturing the intricate interactions between the investigated aftertreatment system, combustion, and exhaust composition. Special emphasis was placed on the formation of intermediate hydrocarbons such as C2H4 and C2H6, despite their concentrations being lower than that of CH4. The analysis of catalytic conversion focused on key species, including H2O, CO2, CO, CH4, C2H4, and C2H6, examining their interactions. After consideration of thermal management and pressure drop, a practical choice of a 400 mm long catalyst with a density of 10 cells per cm2 was selected. Investigations of this catalyst’s specification revealed complete CO conversion and a minimum of 89% hydrocarbon conversion efficiency. Integrating the exhaust aftertreatment system into the air path resulted in a reduction in engine-indicated efficiency by up to 2.65% but did not affect in-cylinder combustion.

The Experimental Investigation of the Effects on the Combustion, Performance, and Emission Characteristics of an RCCI Engine Using Methanol/Diesel Fuel

Reactivity-controlled compression ignition (RCCI) combustion is considered one of the most promising low-temperature combustion (LTC) concepts aimed at reducing greenhouse gases for the transportation and power generation sectors. RCCI combustion mode is achieved by combining different fuel types with low and high temperatures. The aim of this study is to investigate combustion characteristics and reduce nitrogen oxide (NOx) and carbon dioxide (CO2) emissions. In this experimental study, the effects of the RCCI strategy using methanol/diesel fuel on combustion characteristics (ignition delay, combustion duration), engine performance (brake-specific fuel consumption and brake-specific energy consumption), and emissions were examined in a four-cylinder, turbocharged, dual-fuel engine. The experiments were conducted at a constant speed of 1750 rpm at partial loads (40 Nm, 60 Nm, 80 Nm, and 100 Nm). The test results obtained with diesel fuel were compared with the test results obtained with methanol at different mass flow rates. When the results were examined, the minimum ignition delay (ID) occurred at 40 Nm torque, 5.63 crank angle (CA) with M12 fuel, while the maximum ID occurred with M26 fuel at 80 Nm torque, showing an increasing trend as engine load (EL) increased. The highest combustion time (CD) was achieved with M26 fuel at 100 Nm torque, whereas the lowest was achieved with the same fuel (M26) at 40 Nm. While the minimum brake-specific fuel consumption (bsfc) was 45.9 g/kWh for conventional diesel fuel at 40 Nm, the highest bsfc was 104.88 g/kWh for 100 Nm with M26 fuel. Generally, bsfc tends to increase with increasing load. Brake-specific energy consumption (bsec) had the lowest value of 1950.58 kJ/kWh with conventional diesel fuel at 40 Nm and the highest value of 4034.69 kJ/kWh with M26 fuel at 100 Nm. As the methanol content increased, significant improvements were observed in (NOx) and (CO2) emissions, while hydrocarbon (HC) and oxygen (O2) emissions increased as well. Smoke emissions decreased at low loads but tended to increase at high loads.

Trade-off study on environmental aspects of a reactivity controlled compression ignition engine using 1-hexanol and jatropha oil/diesel in dual fuel mode

The present research focuses on a modified engine characteristics that uses jatropha oil blended with diesel as the high reactivity fuel and 1-hexanaol as the low reactivity fuel. Experiments are carried out at peak load at constant injection pressure (600 bar) with different hexanol energy shares (5,10,15, 20, 25, and 30 %). Reactivity-controlled compression ignition (RCCI) engines reduced smoke emissions and oxides of nitrogen by 28 % and 39 % at full load compared to jatropha oil biodiesel. When the 1-hexanol share exceeded 20 %, the thermal efficiency is reduced slightly at full load and increased by 6 % at 20 % 1-hexanol share. The RCCI mode worked better with jatropha oil biodiesel/1-hexanol than the single-fuel mode and significantly increased heat release rate and peak pressure. While boosting engine performance slightly, RCCI mode operation in diesel engines has been observed to reduce 36 % of NOx emissions and 21.2 % of smoke opacity.

Experimental Research on the Carbon Dioxides Reduction Potential by Substitution Gasoline with Ethanol and Propane Under Reactivity Controlled Compression Ignition in a Single Cylinder Engine

In this experiment, it was experimentally investigated the combustion and exhaust characteristics, as well as the thermal efficiency, of RCCI combustion using gasoline, ethanol, and propane as low-reactivity fuels under four operating conditions. For each operating condition, gISNOx was limited to 0.15 g/kWh, and gISSmoke was limited to below 15 mg/kWh. The experiment was conducted by determining the operating conditions that satisfied these limitations and resulted in the highest city thermal efficiency. The low-reactivity fuels were supplied by port injection, while diesel was directly injected into the combustion chamber using a diesel injector. As a result, when gasoline is replaced with low-carbon fuels like ethanol and propane, the reduction in CO2 emissions occurred. Under maximum power conditions, using ethanol allowed for a maximum reduction in CO2 emissions of 6.81%. Depending on the driving conditions, ethanol showed a reduction ranging from 3.60 to 6.81%, while propane exhibited a reduction ranging from 3.10 to 5.64%. Additionally, by substituting with ethanol and propane, the GIE could be improved up to 44.73 and 43.56%, respectively.

Developments in the RCCI engines powered by several alternative fuel types: An overview

The perspective on internal combustion engines (ICEs) has changed because of the step-by-step decrease in oil reserves, environmental concerns, and many other reasons. However, the use of these engines will continue in the coming years. The development of ICEs has accelerated in recent years. As a result, studies on systems that can improve performance and reduce pollution in engines are carried out by many researchers. The basis of the studies carried out in this context is the change in the combustion mode. In other words, the emergence of different combustion modes is given importance by researchers. Among these, many studies have been made on the implementation of the reactivity-controlled compression ignition (RCCI) combustion mode. RCCI engine uses two different fuels. These fuels are low-reactivity (alcohol, gasoline, etc.) and high-reactivity (diesel, biodiesel, etc.) fuels. In addition, the fact that different alternative fuel types can be employed in these engines has made them popular all over the world. This review presents the results of the effects of parameters such as fuel ratio, different injection strategies, exhaust gas recirculation (EGR) rate, compression ratio, and piston geometry on the performance, emissions, and combustion behavior of RCCI engines using both conventional and alternative fuels. This study has been compiled to provide an overview of the current status of the RCCI concept and to offer benefits to researchers.

Low Temperature Combustion Modeling and Predictive Control of Marine Engines

The increase of popularity of reactivity-controlled compression ignition (RCCI) is attributed to its capability of achieving ultra-low nitrogen oxides (NOx) and soot emissions with high brake thermal efficiency (BTE). The complex and nonlinear nature of the RCCI combustion makes it challenging for model-based control design. In this work, a model-based control system is developed to control the combustion phasing and the indicated mean effective pressure (IMEP) of RCCI combustion through the adjustments of total fuel energy and blend ratio (BR) in fuel injection. A physics-based nonlinear control-oriented model (COM) is developed to predict the main combustion performance indicators of an RCCI marine engine. The model is validated against a detailed thermo-kinetic multizone model. A novel linear parameter-varying (LPV) model coupled with a model predictive controller (MPC) is utilized to control the aforementioned parameters of the developed COM. The developed system is able to control combustion phasing and IMEP with a tracking error that is within a 5% error margin for nominal and transient engine operating conditions. The developed control system promotes the adoption of RCCI combustion in commercial marine engines.

Biogas intake pressure and port air swirl optimization to enhance the diesel RCCI engine characteristics for low environmental emissions

Exhaust emission and combustion control in RCCI (reactivity-controlled compression ignition) focused mainly on the direct-injected fuel parameters, urging to investigate the advantages of port-fuel intake parameters. The engine was modified for port injection of Biogas at the valve and RCCI mode. The influence of port swirl ratio (PSR, 0 – 80%) and biogas injection pressure (BIP, 1 – 4 bar) on the diesel RCCI combustion and emissions was tested and optimized at varied loads and 1600 rpm in a port injection at the valve (PIVE) approach. Established kinetic mechanisms were combined with multi-objective optimization to further investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The results show that the radiation absorption triggered by increased CO2 lowers combustion temperature, resulting in prolonged ignition. Setting the airflow to swirl lowers the in-cylinder pressure at elevated BIP while raising the heat generated across the BIPs. Increasing the PSR slows the combustion while BIP speeds up the process. BIP and PSR show great trade-off reduction ability among all emission parameters. The optimum unburned hydrocarbon, nitrogen oxide, particulate, and carbon monoxide emissions for the injection at the valve were found to be 109.58, 0.577, and 2.336 ppm, and 0.103%, respectively, at low-load, low-BIP, and high-PSR. The emissions were lowered by 6.58, 91.26, 80.65, and 13.45% compared to the premixed RCCI mode, respectively. Therefore, introducing low-pressure biogas amid high swirling air at the valve elevates the in-cylinder condition while lowering the emissions, mitigating their environmental implications.

Predicting the effects of direct-injected fuels co-powered by high-CO2 biogas on RCCI engine emissions using kinetic mechanisms and multi-objective optimization

High inert gas content in biogas resulted in poor burning and emissions attributes, though scarcely investigated in reactivity controlled compression ignition (RCCI). Established kinetic mechanisms were combined with multi-objective optimization to investigate, predict, and analyze emissions occurrence and trade-offs for reduced environmental impacts. The work examined the impact of direct-injected high reactivity fuels (HRF) and port-injected Biogas at various inert gas (carbon dioxide, CO2) rates (25 – 45% vol), biogas fractions (40 – 70%), speeds (1600 – 2000 rpm), and loads (4.5 – 6.5 bar IMEP) on emissions of RCCI engine, experimentally. The findings revealed that while engine speeds greatly decreased CO (carbon monoxide) and NOx (nitrate oxide) emissions with rising unburned hydrocarbon (UHC) regardless of HRF employed, higher engine load significantly reduced UHC emissions. Diesel-biogas reduces NOx emissions and performs better in reducing CO and UHC emissions at lower speeds than B5-biogas, except in low-level loads. Although increasing CO2 impact led to a reduction in UHC and CO emissions, the biogas proportion was the most significant variable. The main factor influencing increased NOx emissions was engine load, which is inversely correlated with reduced NOx and increased particulate emissions owing to high CO2 content and biogas proportion. The premixed mode's optimisation outcome confirms the trade-off reduction at 5.5 bar IMEP, 35.586% CO2, and 50% fraction. As a result, running the RCCI engine with direct-injected diesel co-powered in equal proportion with high-CO2 biogas cuts the emissions trade-off dramatically, limiting the environmental repercussions of the emissions.

RCCI combustion of ammonia in dual fuel engine with early injection of diesel fuel

Ammonia has gained considerable attention as a valuable, carbon-free alternative fuel for internal combustion engine (ICE) applications. The growing interest in ammonia's potential as an energy source stems primarily from its advantageous storage and transport properties. The reactivity-controlled compression ignition (RCCI) combustion mode presents a promising avenue for overcoming the challenges intrinsic to conventional diesel engines, such as elevated nitrogen oxides (NOx) and particulate matter (PM) emissions. Additionally, it addresses the limitations of both homogeneous charge compression ignition (HCCI) combustion (limited operational range) and premixed charge compression ignition (PCCI) combustion (diminished power output). The application of an ammonia-based RCCI combustion strategy emerges as a viable pathway for harnessing ammonia as a fuel. In this study, a numerical simulation on a single-cylinder heavy-duty engine operated in RCCI mode is conducted utilizing ammonia and diesel as fuels. The engine is operated at medium load and 910 RPM. The simulation results are validated against experimental data sourced from existing literature. The study investigates the impact of varying ammonia energy fractions, injection timing, and intake valve close temperature (TIVC) on key operational characteristics of the engine including in-cylinder pressure, heat release rate (HRR), combustion efficiency (CE), indicated mean effective pressure (IMEP), and emission levels. The results indicated that increasing the ammonia energy fraction within the RCCI combustion mode, transitioning from 30 % to 70 %, leads to a notable enhancement in IMEP, while maintaining low levels of carbon monoxide (CO), hydrocarbons (HC), unburned ammonia, and nitrous oxide (N2O) as greenhouse gases (GHG). Furthermore, increasing ammonia's energy fraction yielded a discernible reduction in NOx emissions and carbon dioxide (CO2). Conversely, the RCCI combustion mode attained superiority over the dual fuel combustion mode by simultaneously elevating CE and diminishing emissions of GHG, (CO2 and N2O) as well as unburned NH3.

A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine

Article A Visual Study on of HCB/Gasoline Dual-Fuel Combustion Strategy and Premix Ratio in a Diesel Engine Qian Wang *, Botian Guo, Lixuan Cao, Xu Liu, Yi Jiang, and Jiawei Yao School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China * Correspondence: qwang@ujs.edu.cn     Received: 8 November 2023 Accepted: 22 January 2024 Published: 30 January 2024   Abstract: This study investigates the combustion characteristics of hydrogen catalysed biodiesel (HCB) ignited gasoline in an optical engine using the Reactivity Controlled Compression Ignition (RCCI) combustion model. The experiment uses a single injection strategy to determine the optimum injection timing for gasoline ignition by varying the HCB injection timing (-30 to -15° CAATDC) and the ratio of high to low reactivity fuel energy (10% to 30%), to investigate the gasoline premix ratio, and to analyse the flame development characteristics. The results indicate that as the HCB energy ratio increases, the in-cylinder pressure and heat release rate increase significantly, and the in-cylinder combustion temperature improves significantly. As the injection timing is delayed, the combustion phase shifts back, and when the injection timing is close to the upper stop, the in-cylinder combustion pressure and heat release rate increase first increase and then decrease. Based on the results, it can be concluded that optimising the HCB injection timing and energy ratio can effectively control the distribution of the fuel-air mixture in the combustion chamber, thereby improving combustion efficiency and emission performance. By strategically adjusting the injection timing, an ideal balance between fuel stratification and flame propagation can be achieved, which ultimately improves the overall combustion process. The results of this study provide valuable insights for the further development of combustion control strategies and contribute to the development of more efficient and environmentally friendly engine technologies.

Study on Combustion and Soot Formation Characteristics of RCCI Engine with Diesel Mixed with PODE Ignited Gasoline

Article Study on Combustion and Soot Formation Characteristics of RCCI Engine with Diesel Mixed with PODE Ignited Gasoline Qian Wang, Botian Guo, Wenjun Zhong *, Peng Jiang *, and Xu Liu School of Energy and Power Engineering, Jiangsu University, Zhenjiang 212013, China * Correspondence: wj_zhong@ujs.edu.cn (W.Z.); jiangpeng@ujs.edu.cn (P.J.)     Received: 8 November 2023 Accepted: 23 January 2024 Published: 30 January 2024   Abstract: Polymethoxydimethyl ether (PODE) is a promising clean alternative fuel with the potential to improve carbon emissions from internal combustion engines. However, when used as a sole fuel, its low viscosity leads to increased wear on high-pressure pumps and injectors. Furthermore, its low calorific value makes it unsuitable for direct application in diesel engines. Numerous studies have shown that blending PODE with diesel results in lower soot generation throughout the entire combustion cycle in diesel engines. However, the process of reducing in-cylinder soot generation is not yet clear, necessitating further optical diagnostics of in-cylinder combustion. Therefore, the aim of this study is to investigate the influence of PODE/diesel blend combustion on the combustion characteristics and soot generation properties of reactivity controlled compression ignition (RCCI) diesel engines. The study employs an optical engine and conducts experiments using high-speed imaging and two-color pyrometry. Preliminary experiments indicate that a 50% premixed ratio exhibits better heat release and lower soot generation. Thus, this study explores the effects on in-cylinder combustion and soot generation properties by varying the PODE blending ratio and injection strategy under a 50% premixed ratio. Results indicate that with an increase in PODE blending ratio, both peak in-cylinder pressure and heat release rate decrease, and the combustion duration is prolonged. Compared to diesel, the soot content of P20D80 (20% PODE and 80% diesel) and P50D50 (50% PODE and 50% diesel) is 55.22% and 36.55% respectively, while the heat release is 97.89% and 95.39% of that of diesel. The total amount of soot generated was 55.22% and 36.55% of that of direct injection P0D100, the high temperature area of soot was reduced by 52.9% and 73.32% respectively, the stable value of the average soot temperature was reduced by 6.65 K and 20.25 K respectively, and the average KL factor was the stability values were reduced by 10.35% and 16.12% respectively. P50D50 effectively reduces soot generation while maintaining thermal efficiency. Furthermore, an investigation of injection strategy under P50D50 condition reveals that segmented injection results in lower cylinder pressure, peak heat release rate, and total soot generation compared to single injection. The average temperature of the two-stage injection strategy increased, and the average temperature of soot stable time under the operating conditions of D-40/-20, D-35/-20 and D-30/-20 were 2100.85 K, 2210.16 K and 2192.24 K, respectively. The stable values of the average KL factor of soot under the operating conditions of D-40/-20, D-35/-20 and D-30/-20 were 86.52%, 66.62% and 62.79% of those of S-20, respectively. Although it effectively suppresses soot generation, it comes at the cost of sacrificing a portion of heat release.

Multicriteria Decision-Making Technique for Choosing the Optimal Ammonia Energy Share in an Ammonia-Biodiesel-Fueled Reactivity-Controlled Compression Ignition Engine.

Low-temperature combustion paired with the use of carbon-free ammonia and carbon-neutral biofuels is a novel approach for improving performance, reducing greenhouse gases, and reducing regulated emissions. Reactivity-controlled compression ignition (RCCI), a low-temperature combustion technology, dramatically reduces NOx and smoke emissions compared to traditional engines. Ammonia can be projected as a good transit fuel in the journey toward achieving net zero emissions and cleaner energy. This study examines the impact of ammonia energy premixing fraction (AEPF) (20, 30, 40, and 50%) as a low-reactive fuel (LRF) and algal biodiesel as a high-reactive fuel on the performance and emission characteristics of a single-cylinder, water-cooled 3.5 kW CI engine at a constant speed of 1500 rpm under various loading conditions. The research results indicate that the 40% ammonia share RCCI mode exhibited a reduction in carbon dioxide (CO2) by 14.16%, nitrogen oxide (NOx) by 22.6%, and smoke by 42.1%, with an 11.5% improvement in thermal efficiency compared to the neat biodiesel-fueled conventional engine. Furthermore, the analytical hierarchy process (AHP) will be used in conjunction with the technique for order of preference by similarity to ideal solution (TOPSIS) of multiple criteria decision-making techniques to determine the optimal energy share in the RCCI combustion with the goal of achieving superior thermal efficiency and lower emissions. According to the AHP-TOPSIS study findings, AEPF40 is the best choice for all engine loads.

Machine Learning-Based Modeling and Predictive Control of Combustion Phasing and Load in a Dual-Fuel Low-Temperature Combustion Engine

<div>Reactivity-controlled compression ignition (RCCI) engine is an innovative dual-fuel strategy, which uses two fuels with different reactivity and physical properties to achieve low-temperature combustion, resulting in reduced emissions of oxides of nitrogen (NO<sub>x</sub>), particulate matter, and improved fuel efficiency at part-load engine operating conditions compared to conventional diesel engines. However, RCCI operation at high loads poses challenges due to the premixed nature of RCCI combustion. Furthermore, precise controls of indicated mean effective pressure (IMEP) and CA50 combustion phasing (crank angle corresponding to 50% of cumulative heat release) are crucial for drivability, fuel conversion efficiency, and combustion stability of an RCCI engine. Real-time manipulation of fuel injection timing and premix ratio (PR) can maintain optimal combustion conditions to track the desired load and combustion phasing while keeping maximum pressure rise rate (MPRR) within acceptable limits.</div> <div>In this study, a model-based controller was developed to track CA50 and IMEP accurately while limiting MPRR below a specified threshold in an RCCI engine. The research workflow involved development of an imitative dynamic RCCI engine model using a data-driven approach, which provided reliable measured state feedback during closed-loop simulations. The model exhibited high prediction accuracy, with an <i>R</i><sup>2</sup> score exceeding 0.91 for all the features of interest. A linear parameter-varying state space (LPV-SS) model based on least squares support vector machines (LS-SVM) was developed and integrated into the model predictive controller (MPC). The controller parameters were optimized using genetic algorithm and closed-loop simulations were performed to assess the MPC’s performance. The results demonstrated the controller’s effectiveness in tracking CA50 and IMEP, with mean average errors (MAE) of 0.89 crank angle degree (CAD) and 46 kPa and Mean absolute percentage error (MAPE) of 9.7% and 7.1%, respectively, while effectively limiting MPRR below of 10 bar/CAD. This comprehensive evaluation showcased the efficacy of the model-based control approach in tracking CA50 and IMEP while constraining MPRR in the dual-fuel engine.</div>

Effect of split injection strategy of diesel fuel on multi-stage heat release and performance of a RCCI engine fueled with diesel and natural gas

Reactivity controlled compression ignition (RCCI) combustion is a advanced low temperature combustion concept to reduce CO2 and brake the trade-off between NOx and PM emissions for next generation compression ignition (CI) engines. However, it leads to the more complex multi-stage heat release in diesel/natural gas (NG) dual fuel engines and is criticized for extra-high methane and carbon monoxide emissions. Using the existing methods, it is difficult to effectively quantify the contribution of the accumulated heat release (AHR) at each stage to the whole combustion process and to create their relevance to the performance and emissions in the RCCI engines.In this paper, experiments were conducted on a ship diesel/NG dual-fuel engine at a load of 25 %. A new identification and quantitative analysis method of multi-stage heat release is proposed, and the coupling effects of the diesel split injection parameters on the multi-stage heat release and performance in the RCCI engine were revealed. The results show that the new method is not only available for analyzing the combustion of traditional CI engines but also is more effective for identifying the multi-stage combustion in RCCI engines. For the increased pre-injection ratio (PR), as the start of first injection (SOI-I) and the start of second injection (SOI-II) advance, the AHR in Stage-I (Q-Stage-I) decreases, and the increased Q-Stage-III lead to the improved indicated thermal efficiency (ITE > 49 %). Meanwhile, methane (CH4), non-methane hydrocarbon (NMHC) and carbon monoxide (CO) emissions can be reduced by more than 50 %, while nitrogen oxides (NOx) emissions increase. The impact significance of SOI-II on Q-Stage-I and Q-Stage-III is higher, their values are + 65.88 % and −51.04 %, respectively, and the Q-Stage-II is mainly controlled by SOI-I. The impact significance of Q-Stage-III on ITE is the highest about + 69.43 %. Q-Stage-I shows a higher positive correlation with CH4, NMHC and CO emissions although the proportion of Q-Stage-I is far smaller than that of Q-Stage-II and Q-Stage-III. Therefore, the simultaneous reduction of incomplete combustion products and NOx emission can be achieved by reasonably adjusting split injection parameters.

A relative comparison of HCCI, PCCI, and RCCI combustion strategies: an alternative fuels perspective

Low temperature combustion (LTC) strategies have the potential for simultaneous reduction in oxides of nitrogen (NOx) and soot emissions while achieving higher thermal efficiency. Commercial widespread implementation of LTC strategies demands addressing several challenges, including narrow operating load range, lack of ignition timing control, and reducing high unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. These challenges could be because the conventional engine design and fuels cannot adapt well to LTC modes. Thus, replacing conventional diesel fuel with suitable alternative fuels for LTC strategies is essential. In the present work, three LTC strategies, Homogenous Charge Compression Ignition (HCCI), Premixed Charge Compression Ignition (PCCI), and Reactivity Controlled Compression Ignition (RCCI), are compared with conventional diesel combustion in a production, light-duty diesel engine from an alternative fuel perspective to come up with a befitting strategy and fuel to achieve wider operating range and lower emissions. The fuel selection strategy based on the fundamental fuel property requirements of the three LTC strategies has been discussed in detail. The baseline reference data is fixed by comparing three LTC strategies with conventional diesel combustion using diesel and gasoline as reference fuel at 40% load, the maximum common achievable load among the three LTC strategies. This is followed by an investigation of the effect of alternative fuels across three LTC strategies to address the shortcomings of the LTC strategies. The results show that the engine operating load range could be extended, and HC and CO emissions are reduced significantly with alternative fuels in the three LTC strategies.

Experimental Studies to Reduce Usage of Fossil Fuels and Improve Green Fuels by Adopting Hydrogen–Ammonia–Biodiesel as Trinary Fuel for RCCI Engine

Experimental Studies to Reduce Usage of Fossil Fuels and Improve Green Fuels by Adopting Hydrogen–Ammonia–Biodiesel as Trinary Fuel for RCCI Engine