Reactivity Controlled Compression Ignition Combustion Research Articles

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.

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.

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.

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.

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>

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

Analysis of the Vibrational Behavior of dual-fuel RCCI combustion in a Heavy-Duty Compression Ignited Engine fueled with Diesel-NG at Low Load

In the field of internal combustion engines, the Low Temperature Combustions (LTC) appear to have the potential to reduce the formation of both soot and nitrogen oxides. One of the most promising LTC is Reactivity Controlled Compression Ignition (RCCI) which is based on the combustion of a lean low reactivity fuel-air mixture generated in the intake manifold and autoignited by small injections of high reactivity fuel introduced at high pressure in the combustion chamber. By the combination of net-zero natural gas and biodiesel, such LTC methodology might represent a suitable solution moving toward zero-emissions in transportation sector.Despite the potential to reduce pollutant emissions, Low Temperature Combustion strategies face a challenge in controlling the angular position where the combustion takes place which can be overcome by a proper management of the high-pressure injections.One potentially interesting application is related to trucks, mainly because they have long periods of idling, since emissions can be drastically reduced by means LTC. A single cylinder research engine for heavy duty application is operated under steady state conditions at low load and speed to analyze the possibility of controlling the engine behavior in dual fuel RCCI mode. The results indicate that the combustion mode switches from the dual-stage to gaussian within a narrow angular range. A further advance of the start of injection can generate misfires and significant variations in typical combustion indexes, while a delayed start of injection can cause impulsive combustion that rises the cylinder temperature and results in high-frequency pressure oscillations inside the combustion chamber. These oscillations are related to the combustion chamber typical resonance frequency, and if relevant in amplitude and persist for a long time, they might generate a potential source of failures.

Prediction of RCCI combustion fueled with CNG and algal biodiesel to sustain efficient diesel engines using machine learning techniques

This study used microalgae biodiesel as a high-reactive fuel directly injected along with various Compressed Natural Gas (CNG) energy shares (10, 20, 30, and 40%) as low-reactive fuel injected into the intake system. The experiments are performed in a single-cylinder, water-cooled, 1500 rpm, 3.5 kW power Compression Ignition (CI) engine under various loading conditions to examine the effects of CNG energy share on performance and emissions in Reactivity Controlled Compression Ignition (RCCI) combustion mode. The study found that the 30%CNG share decreased Nitrogen oxides (NOx) and smoke by 25 and 31%, as well as an increase in thermal efficiency of 4.35% in comparison to traditional biodiesel combustion. Finally, two machine learning (ML) models, namely the Gradient Boosting Regressor (GBR) and LASSO (Least Absolute Shrinkage and Selection Operator) Regression, were developed for predicting the dependent variables individually from the independent variables. Both the LASSO and GBR models achieved high accuracy with R2 values of 0.98–0.99 and relatively low Root Mean Square Error (RMSE) values.

Optical diagnostics of premixed energy ratio effects on RCCI combustion and soot formation characteristics under low load conditions

The study aims to explore the feasibility of using alternative fuels to achieve a high premixed energy ratio in reactivity-controlled compression ignition (RCCI) engine and reduce combustion difficulties at low loads. Specifically, the effects of premixed energy ratios (70%, 80%, and 90%) on combustion and soot formation characteristics were studied using ethanol-gasoline fuel blend (E10) and hydrogenated catalytic biodiesel (HCB) fuels in an optical engine under light load conditions. To investigate the flame characteristics and soot distributions, natural flame luminosity and two-color methods by wavelength integration were employed. The experimental results demonstrate that the RCCI engine, when fueled with E10 and HCB, achieved reliable ignition under the given test conditions. The study revealed that an increase in the premixed energy ratio results in a longer ignition delay, lower in-cylinder pressure, and heat release rate. This promotes a more homogeneous combustion process, which in turn leads to a slower combustion rate. Additionally, chemiluminescence imaging revealed that variations in the premixed energy ratio had a significant impact on the generation of flame kernels, the properties of flame propagation, and the evolution and distribution of soot. The areas where flame kernels are generated gradually shifted from the near-wall region towards the spray region. The premixed flame front transitioned from propagating from the near-wall region towards the center to propagating outward along the spray direction. Increasing the premixed energy from 70% to 90% significantly reduced the high-temperature and soot concentration regions, particularly at the intersection of the flame fronts, resulting in a significant decrease in the integrated KL factor by 75.69% and 96.41%, respectively. Based on an analysis of combustion and soot formation characteristics, a higher premixed ratio (90%) results in a more favorable flame propagation, cleaner combustion process, and a higher IMEP at low load conditions. These findings offer valuable insights for optimizing RCCI combustion, aiming to enhance engine performance under low load conditions with higher premixed energy ratios.

Modeling study of the ignition characteristics of directly injected 1,3-Cyclohexadiene in surrogate Gasoline/Air under RCCI combustion conditions

In this work a validated chemical kinetic model of the combustion of multicomponent gasoline surrogate fuels containing 680 reactions of 152 species has been used to simulate conditions reminiscent of those of Reactivity Controlled Compression Ignition (RCCI) in order to evaluate 1,3-cyclohexadiene (CYC6H8) as the high reactivity directly injected fuel and a gasoline surrogate fuel as the low reactivity premixed fuel. A single-zone modeling approach was adopted using a modified Cantera example describing the simulation of a gaseous Diesel-type internal combustion engine. The adaptable chemical structure of CYC6H8 to cis-1,3,5-hexatriene (lC6H8), load, start of injection and premixed fuel mass fraction were varied in order to analyze the potential of CYC6H8 as an ignition enhancer. Results have been compared to n-heptane and show that CYC6H8 and its isomer lC6H8 have the potential to be used as the high reactivity directly injected fuel in dual-fuel RCCI combustion, especially at high load conditions. For increased load, the ignition promoting effect is more pronounced at lower premixed fuel mass fractions and less affected by a delayed start of injection. The ignition promoting effect of lC6H8 is more pronounced than CYC6H8 for a decreasing premixed fuel mass fraction. Results from the kinetic analysis indicate that at increased concentrations of lC6H8, the thermal effects are becoming more significant.

Experimental evaluation and neural network modelling of reactivity-controlled compression ignition engine using cashew nut shell oil biodiesel-alumina nanoparticle blend and gasoline injection

The current desire is for enhanced combustion techniques that improve engine efficiency while successfully reducing emissions. Reactivity controlled compression ignition (RCCI) combustion encompasses the ability to increase fuel efficiency and decrease oxides of nitrogen emissions compared to conventional compression ignition (CI) combustion. This study presents a novel investigation that focuses on the capabilities of the RCCI engine, utilizing a unique combination of gasoline and diesel blended with cashew nut shell oil biodiesel (CNSOB) and the addition of aluminum oxide (Al2O3) nanoparticles. CNSOB extracted from waste shell has an oil content of 30–35 wt% yield. The cost of the oil range between is ₹. 40–50 in India. The engine operates on a blend of gasoline, known for its low reactivity, and diesel blended with CNSOB, a renewable and environmentally friendly alternative to diesel. The effects of varying proportions of the blend (B0, B50, and B100) and the addition of Al2O3 nano additive (25 and 50 ppm) on the efficiency and emissions of RCCI combustion are comprehensively analyzed experimentally. The results reveal that RCCI combustion significantly improves engine performance compared to compression ignition engines. A 2% increase in maximum in-cylinder pressure indicates improved combustion efficiency. Furthermore, fuel economy is improved by up to 2% due to increased engine brake thermal efficiency (BTE). Further, nitrogen oxide (NOx) emissions are reduced by up to 54% during RCCI combustion, demonstrating its potential for reducing pollution. Utilizing CNSOB biodiesel results in a 50% reduction in hydrocarbon (HC) emissions as well as a 17% reduction in carbon monoxide (CO) emissions. This indicates improved air quality and reduces environmental pollution. The incorporation of Al2O3 nano additives into the RCCI engine results in a 5% reduction in brake specific energy consumption (BSEC), showing better engine energy efficiency. Based on the results of the investigation, a neural network framework was developed. The neural network framework was developed to replicate both the efficiency and pollution parameters of the RCCI engine using the experimentally determined relationship between input factors and output parameters. The neural network model was trained using 70% of the available data, and its performance was evaluated by comparison of predictions with the corresponding observations from experiments. The forecast outcomes matched those of the trial, demonstrating the artificial neural network (ANN) models effectiveness and precision in predicting the engine performance and emissions.

Ultra-low emission power generation utilizing chemically stabilized waste plastics pyrolysis oil in RCCI combustion concept

Emission standards in European Union, designed to reduce the environmental impact of power generation, present a significant challenge for fast-response distributed power generation systems based on internal combustion engines. Regulated emissions, such as NOx and particulate matter present a major concern due to their adverse number of environmental and health effects. Simultaneously, European Union strives towards sustainable management of plastic waste and seeks the ways for its upcycling and production of new fuels and chemicals. As an answer to the presented challenges, the present experimental study addresses the potential for use of chemically stabilized Waste Plastics Oil (WPO), a product of pyrolysis process of waste plastics in a Reactivity Controlled Compression Ignition (RCCI) combustion concept. To establish a reactivity-controlled combustion, the study uses a combination of methane (a model fuel for biomethane) and WPO to a) simultaneously reduce NOx and particulate matter emissions due to low local combustion temperatures and a high degree of charge homogenization and b) address waste and carbon footprint reduction challenges. Through experiments, influence of direct injection timing and energy shares of utilized fuels to in-cylinder thermodynamic parameters and engine emission response were evaluated in engine operating points at constant indicated mean effective pressure. Acquired results were deeply investigated and benchmarked against compression ignition (CI) and RCCI operation with conventional diesel fuel to determine potential for WPO utilization in an advanced low-temperature combustion concept. Results show that chemically stabilized WPO can be efficiently utilized in RCCI combustion concept without adaptation of injection parameters and that with suitable control parameters, ultra-low emissions of NOx and PM can be achieved with utilized fuels. For diesel/methane mix, NOx and PM emissions were reduced compared to conventional CI operation for 82.0% and 93.2%, respectively, whereas for WPO/methane mix, NOx and PM emissions were reduced for 88.7% and 97.6%, respectively, which can be ascribed to favourable chemical characteristics of WPO for the utilized combustion concept. In the least favourable operating point among those studied, indicated mean effective pressure covariance was kept below 2.5%, which is well below 5% being considered the limit for stable engine operation.

Auto-Ignition and Flame Characteristics of Ammonia Reactivity-Controlled Compression Ignition Combustion in Comparison with Methane

Auto-Ignition and Flame Characteristics of Ammonia Reactivity-Controlled Compression Ignition Combustion in Comparison with Methane

Comprehensive analysis of combustion behaviors of hydrogen (H2)/diesel reactivity-controlled compression ignition (RCCI) in a light-duty diesel engine

In this study, a comprehensive analysis of the combustion behaviors of hydrogen (H2)/diesel reactivity-controlled compression ignition (RCCI) was conducted toward the achievement of reliable and flexible combustion control of H2 RCCI. The interplay between H2 and the direct-injection (DI) high-reactivity fuel in RCCI combustion was revealed under various operating conditions, and the potential of H2/diesel RCCI in enhancing engine performance was excavated. The results suggested that under the single DI strategy, the maximum indicated thermal efficiency (ITE) of H2 RCCI is considerably higher than that of gasoline RCCI. Compared with the single DI strategy, using the double DI strategy can significantly improve ITE and nitrogen oxides (NOx) emissions simultaneously for H2/diesel RCCI. Under the double DI strategy, the ignition and combustion of H2 are more sensitive to intake boost than gasoline in RCCI. Meanwhile, compared with gasoline, H2 can inhibit to some extent the low-temperature heat release from the DI high-reactivity fuel in RCCI. By evaluating the emission performance of H2/diesel RCCI under different double DI strategies, it was found that NOx emissions of H2/diesel RCCI are mainly dominated by the homogeneity of the DI fuel/air mixture but not the combustion rate. In addition, increasing the premixed ratio can effectively improve combustion stability, ITE, NOx, and soot simultaneously with reduced peak pressure rise rate for H2/diesel RCCI. Attributed to the absence of carbon elements in H2, the soot emissions of H2 RCCI are considerably lower than that of gasoline RCCI.

Influence of injection strategies on ignition patterns of RCCI combustion engine fuelled with hydrogen enriched natural gas

The depletion of fossil fuel and the concerns for harmful emissions and global warming has instigated researchers to use alternative fuels. Hydrogen (H2) and natural gas (NG) are attractive fuels for internal combustion engines. The dual-fuel combustion strategy is promising to reduce emissions with efficient engine operation. The concern for using NG in this strategy is the lower efficiency at low load conditions and the emission of exhaust gases like carbon monoxide and unburnt hydrocarbon. Mixing fuel with a wide flammability limit and a faster burning rate with NG is an effective method to compensate for the limitations of using NG alone. Hydrogen (H2) is the best fuel added with NG to cover NG limitations. This study investigates the in-cylinder combustion phenomenon of reactivity-controlled compression ignition (RCCI) engines using hydrogen-added NG as a low-reactive fuel (H2 addition to NG on a 5% energy basis) and diesel as a highly reactive fuel. The numerical study was done on a 2.44 L heavy-duty engine using CONVERGE CFD code. Three low, mid, and high load conditions were analyzed in six stages by varying the diesel injection timing from −11 to −21 O after top dead centre (ATDC). The H2 addition to NG had shown deficient harmful emissions generation like carbon monoxide (CO) and unburnt hydrocarbon with marginal NOx generation. At low load conditions, the maximum imep was achieved at the advanced injection timing of −21OATDC, but with the increase in load, the optimum timing was retarded. The diesel injection timing varied the optimum performance of the engine for these three load conditions.

Investigations on reactivity controlled compression ignition combustion with different injection strategies using alternative fuels produced from waste resources

Reactivity-controlled compression ignition (RCCI) is a promising low-temperature combustion (LTC) strategy that results in low oxides of nitrogen (NOx) and soot emissions while maintaining high thermal efficiency. At the same time, RCCI leads to increased unburned hydrocarbon (HC) and carbon monoxide (CO) emissions in the exhaust, particularly under low loads. The current work experimented novel port-injected RCCI (PI-RCCI) strategy to overcome the high unburned emission limitations at low load conditions in RCCI. PI-RCCI is a port injection strategy in which low-reactivity fuel (LRF) is injected using a low-pressure injector, and the high-reactivity fuel (HRF) is injected through a high-pressure common rail direct injection (CRDI) injector. The low volatile HRF is injected into a heated fuel vaporizer maintained at 180°C in the intake manifold during the suction stroke. Modifying a single-cylinder, light-duty diesel engine with the necessary intake and fuel injection systems allows engine operation in both RCCI and PI-RCCI modes. Alternative fuels from waste resources such as waste cooking oil biodiesel (WCO) and plastic waste oil (WPO) are used as the HRF and LRF fuel in RCCI and PI-RCCI. To achieve maximum thermal efficiency in RCCI, the premixed energy ratio and the start of injection of the direct-injected fuel are optimized at all load conditions. The engine performance and exhaust emissions characteristics in PI-RCCI are compared with RCCI as a baseline reference. The results show a 70% and 48% reduction in CO and HC emissions, respectively, in PI-RCCI than in RCCI. Further, the brake thermal efficiency (BTE) was enhanced by around 20%, and the brake-specific fuel consumption (BSFC) was reduced by 13% in PI-RCCI. The NOx emissions decreased without any considerable changes in soot emission in PI-RCCI. The current study shows that fuels derived from waste resources can be used in RCCI and PI-RCCI modes with better engine performance and lower emissions.

Optimizing RCCI combustion for improved engine performance under low load conditions: Impact of low-reactivity fuel and direct injection timing

The objective of this study is to explore the challenges associated with the RCCI (Reactivity Controlled Compression Ignition) concept under low loads, where there may be insufficient combustion or misfires caused by a lean fuel mixture in the combustion chamber. To address this issue, optical diagnostics and post-processing techniques are utilized to investigate the effects of low-reactivity fuel and direct injection timing on combustion and flame characteristics in a dual-fuel engine under such conditions. The study tested three different low-reactivity fuels and five different direct injection (DI) timings while maintaining hydrogenated catalytic biodiesel (HCB) as a high-reactivity fuel. The research findings reveal that an increase in ethanol content results in longer ignition delay and a displacement of the ignition kernels towards the downstream of the fuel stream. Consequently, a more homogeneous combustion process and slower flame propagation occur, ultimately reducing the combustion intensity, cylinder pressure, and peak apparent heat release rate. Premixing E10 allows for a higher indicated mean efficient pressure (IMEP) of 0.20 MPa, exceeding E0 by 0.02 MPa and E100 by 0.05 MPa. The research also highlights that delaying the DI timing of HCB reduces ignition delay time and creates a higher concentration gradient of the combustible mixture, resulting in a higher apparent heat release rate and shorter combustion duration. Additionally, natural combustion luminosity images indicate that delaying the DI timing substantially impacts the characteristics of flame kernels generation and propagation. The ignition kernels formed shifted gradually from the near-wall region to upstream region of the spray, as the blue flame area and front propagation speed showed a significant increase. Retarded DI timing can achieve more favorable flame propagation and a higher IMEP under low loads conditions with a higher premixed energy ratio, while effectively reducing the impact of spray-wall impingement and pool burning phenomena. These findings provide insights into optimizing RCCI combustion for improved engine performance under low load conditions.

Reactivity enhancement of natural gas/diesel RCCI engine by adding ozone species

Reactivity controlled compression ignition (RCCI) is an alternative combustion strategy with the potential of significant advantages in terms of increasing thermal efficiency together with reduction of NOx and soot emissions. The RCCI engines have been encountered not to be applicable broadly since they suffer from some difficulties mainly contributed to the controllability of combustion and limited operating ranges. The difficulties become even worse where low-reactivity fuels like natural gas (NG) are applied. Ozone gas, a chemical species with an extreme level of reactivity, can improve the combustion efficiency along with the advancement of combustion phasing in the RCCI engine. In this study a multidimensional computational fluid dynamic (CFD) which is coupled with proper detailed chemical kinetic mechanisms is employed to investigate the influence of ozone addition (i.e., 10, 100 and 1000 ppm) to air-fuel mixture with different initial conditions (e.g., intake temperature and equivalence ratio), on the performance and emissions characteristics of the RCCI engine. The results imply that the addition of even low concentrations of ozone (10 ppm) have considerable influences on the RCCI combustion characteristics. Addition of ozone by a distinct quantity not only can enhance the combustion phasing controllability, but also can extend the operating range of the RCCI engine in both lower intake air temperature and the lower fraction of the high-reactive fuel. From the results it is conceived that by adding 1000 ppm ozone into the air-fuel mixture, it is possible to reduce the diesel fuel fraction from 20% to 10% and intake air temperature from 355 K to 335 K, respectively.

Experimental and kinetic modeling studies on the interaction of DMM3-isooctane blends during the low-temperature oxidation

Reactivity controlled compression ignition (RCCI) engines have been extensively investigated in the past decade due to its good performance in balancing the NOx-soot trade off relationship and controlling the heat release rate. However, studies on the interaction between the reactive and inert fuels are scarce, which is critical for regulating the RCCI combustion process. In this study, the interaction mechanism between polyoxymethylene dimethyl ethers (DMM3) and isooctane during the low-temperature oxidation was investigated through experiments and simulations. The low-temperature oxidation experiments were conducted in a jet-stirred reactor (JSR) at near atmospheric pressure with different blending ratios. A detailed DMM3-isooctane mechanism containing 2896 species and 9676 reactions was developed and fully validated with the experimental results. In addition, an impact factor fw was proposed to quantitatively analyze the influence degree of interaction between fuel and intermediate species. The results indicate that the low-temperature oxidation of isooctane is triggered and significantly enhanced in the blending fuels. The OH radicals generated by DMM3 are crucial to trigger the low-temperature reaction of isooctane and always play a dominant role in the whole isooctane oxidation process. In addition, isooctane reveals an intense inhibition on the formation of two key intermediate species of DMM3, i.e., methyl formate and methoxymethyl formate. This inhibitory effect ranges from the beginning of low-temperature oxidation of DMM3 to the end of the NTC process (580 K ∼ 750 K). When the temperature is higher than 800 K, the inhibitory effect of isooctane on methyl formate and methoxymethyl formate is significantly weakened and negligible. In addition, the blending of inactive isooctane will result in an oxygen-rich environment for DMM3 during the low-temperature oxidation, which will accelerate the formation of methyl formate and methoxymethyl formate. However, this promoting effect is limited, compared with inhibiting effect of isooctane.