Reactivity Controlled Compression Ignition Mode Research Articles

Split Injection Timing Optimization in Ammonia/Biodiesel Powered by RCCI Engine

Employing carbon-neutral (NH3) and low carbon footprint (biodiesel) fuels in Reactivity Controlled Compression Ignition (RCCI) engine mode is one possible method for minimizing carbon emissions in diesel engines. In this study, a Compression Ignition (CI) engine was customized to run in RCCI mode, employing High Reactive Fuel (HRF) as biodiesel and Low Reactive Fuel (LRF) as ammonia (NH3). Based on our earlier findings, the proportion of ammonia in premixing is fixed at 40%. In the first phase, the primary injection timing of the algal biodiesel varied between 12 and 21°CA bTDC at a preset pre-injection timing of 46°CA bTDC. In the next phase, the pre-injection time varied between 46 and 54°CA bTDC, with the optimal main injection time being 18°CA. The result suggested that the optimal main and pre-injection at 18 and 58°CA bTDC increased the Cylinder Pressure (CP) by 30.1%, and peak HRR and combustion phase angle were advanced. Brake Thermal Efficiency exhibited an 11% enhancement, with Brake Specific Energy Consumption decreasing by 24.1%. Nitrogen Oxide levels saw an increase of around 39.5%. In contrast, reductions of 19.2%, 23.5%, 39.7%, and 21.7% were observed in Hydrocarbons, Carbon Monoxide, smoke emissions, and Exhaust Gas Temperature, respectively, compared to the single injection under full load conditions.

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.

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.

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.

Estimation of assorted injection schedules on hydrogen-diesel dual fuel and reactivity controlled compression ignition modes in a medium duty automotive engine

Intention of this research is to comprehend the impact of injection parameters on dual fuel and RCCI combustion strategies using hydrogen as the primary fuel and diesel as the ignition source. The study also aims to achieve a smooth transition between these two modes. In this experimental analysis, the quantity of hydrogen and diesel fuel has been equally divided. Hydrogen fuel has been inducted through intake manifold whereas diesel has been injected directly into the cylinder. The quantity of diesel injected is split between two pulses and studied for combustion, performance and emission attributes by altering the timing of first pulse injection whilst maintaining a constant second pulse injection timing. The results show that splitting the diesel fuel quantity equally between two pulses produces the optimum outputs for the study. The research proposes a first pulse of 30° bTDC for hydrogen-diesel dual fuel (HDDF) mode whereas, for hydrogen-diesel RCCI (HDRCCI) mode of combustion, the best first pulse injection timing has been selected as 60° bTDC. The experiment accomplished a smooth transition between HDDF mode and HDRCCI mode by gradually advancing the injection timing without disturbing the performance parameters significantly while accomplishing noteworthy reduction in NOx and negligible variations in other emission parameters.

Ozone-assisted combustion and emission control in RCCI engines: A comprehensive study

This paper presents an investigation into the combustion and emission characteristics of reactivity-controlled compression ignition (RCCI) engines using ozone seeding, which is known as one of the most highly oxidizing chemical species. The study aims to address challenges pertaining to combustion control and emissions deterioration. Therefore, the current work investigates the RCCI mode of operation in a single-cylinder diesel engine with intake air that has been seeded with ozone by introducing conventional diesel fuel as a high-reactivity fuel using a high-pressure direct injection method and iso-octane as a low reactivity fuel using a low-pressure port injection method. In the experimental study, different ozone concentrations up to 300 ppm and three different energy-based premixed ratios of low reactivity fuel from 0% to 45% with a 15% rise rate were examined under various engine loads and constant engine speed. The methodology used in this research provided for simultaneous decreases in unburned hydrocarbon (HC) emissions and smoke opacity for RCCI engines. According to the experimental findings, simultaneous utilization of RCCI mode and ozone seeding led to a decrease of up to 36% in HC emissions and a reduction of up to 98.7% in smoke opacity. Moreover, nitrogen oxides (NOx) emissions were reduced by up to 39.5% at 20% engine load, whereas carbon monoxide (CO) emissions exhibited a decrease of up to 46% at 60% load. The RCCI mode also yields significant reductions in pollutant emissions and notable increases in brake thermal efficiency (BTE) when compared to the conventional diesel mode (CDM). In conclusion, this experimental study presents a promising solution for addressing emissions deterioration in RCCI engines while simultaneously achieving reductions in pollutant emissions.

An optical investigation on the effects of split-injection on hydrogenated catalytic biodiesel/gasoline dual-fuel engine under cold start conditions

Reactivity-controlled compression ignition (RCCI) mode has emerged as a promising technology for internal combustion engines, offering precise combustion phase control and the potential to meet stringent emission regulations. However, RCCI mode faces challenges, particularly misfiring during cold start conditions. This study proposes a solution by utilizing hydrogenated catalytic biodiesel (HCB) as a pilot fuel for gasoline and implementing a split-injection strategy to address the challenge. Experimental research was conducted on an optical engine under cold start conditions, incorporating three split-injection strategies: P30M70 (30 % main-injection and 70 % pilot-injection), P50M50, and P70M30. The results demonstrate that although gasoline can only be ignited by the main-injected HCB under coldstart conditions, the in-cylinder environment becomes more dynamic due to the pilot-injection. Consequently, split-injection reduces ignition delay by up to 7.09 °CA and shortens the combustion stage compared to single-injection. Among the various injection strategies examined, P30M70 demonstrated outstanding in-cylinder heat release performance, surpassing other split-injection strategies by up to 26.77 J/CAD, and outperforming the single-injection by 22.94 J/CAD. Visualization tests indicate that applying the P30M70 strategy leads to higher soot production under conditions of delayed main-injection timing (-15 °CA ATDC). However, the peak flame area under cold-start conditions is 53.16 % greater than P50M50 and 71.28 % greater than P70M30, highlighting excellent flame propagation characteristics. The average in-cylinder temperature suggests that a larger visible flame area contributes to engine warming. Despite the inherent trade-off, the dual-fuel mode of HCB/gasoline proves suitable for RCCI engines, with the P30M70 split-injection strategy being recommended for the cold start stage.

Combustion Parametric Investigations of Methanol-Based RCCI Internal Combustion Engine and Comparison with the Conventional Dual Fuel Mode

Reactivity-controlled compression ignition (RCCI) is an advanced combustion mode. Its uses two fuels with different physical and chemical properties to form a combustible mixture with active stratification. RCCI can flexibly control the combustion process by changing the concentration and activity of the combustible mixture. It can also reduce the emission of NOx and particulate matter in the engine without significantly reducing the thermal efficiency. Among various fuel combinations, methanol as an oxygen-containing fuel, has a high latent heat of vaporization, which is conducive to reducing combustion temperature and achieving low-temperature combustion. This experimental study explores the potential of Methanol-Diesel Reactivity Controlled Compression Ignition (RCCI) in achieving low emissions and high thermal efficiency and compares this with the conventional dual fuel mode. Low-temperature combustions such as Reactivity Controlled Compression Ignition (RCCI) have been shown to be a promising way to reduce pollutants at the exhaust, i.e. NOx and soot emissions. and increase the thermal efficiency of future engines. The methanol to diesel energy share (MDES) could be enhanced to 56% in the RCCI mode with proper setting of the injection parameters from 45% in the dual fuel mode. A higher quantity in the second diesel pulse that occurred close to TDC led to higher thermal efficiency and good combustion stability. Engines working in a dual-fuel mode need special conditions to ignite an air-fuel mixture without a spark plug in a good moment with high combustion efficiency.

Experimental investigation on the effect of injection timing and injection duration of low reactive fuels on RCCI mode of combustion operated with plastic pyrolysis oil

The goal study is to investigate the effect of low reactive fuels (LRFs) injection timing and duration of injection on a reactivity-controlled compression ignition (RCCI) engine. The diesel, mixtures of Karanja oil methyl ester (KOME), plastic pyrolysis oil (PPO) and ethanol are used as LRFs. The examined LRFs have the injection timings (ITs) of 40°ATDC, 45°ATDC, and 50°ATDC. Additionally, the influence of different LRFs injection durations (IDs) of 3, 6, and 9 ms, on the RCCI mode of combustion is included in the present work. The entire experimental process is performed at 75% of the rated power. According to the findings, at IT of 45°ATDC and ID of 6 ms, the Diesel-Gasoline mixture has the highest brake thermal efficiency (BTE) of all the ITs and IDs examined. Nitric oxide (NOx) emissions are higher for all ITs and IDs but smoke, carbon monoxide (CO), and hydrocarbon (HC) emissions are lower for the Diesel-Gasoline mixture compared to other fuel mixtures. Diesel-Gasoline produces a greater peak pressure rise (PPR) compared to other test samples at all ITs and IDs.

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.

Experimental Investigation of the Performance and Unburned Methanol, Formaldehyde, and Carbon Dioxide Emissions of a Methanol-Diesel Dual-Fuel Engine

In the context of global efforts to pursue carbon neutrality, the methanol-diesel reactivity controlled compression ignition (RCCI) combustion has become a promising strategy for diesel engines to reduce emissions with higher thermal efficiency. To further improve the fuel economy of the methanol–diesel RCCI engine and reduce its unregulated emissions, the effects of methanol substitution rate (MSR) and exhaust gas recirculation (EGR) on fuel economy, CO2, MeOH, and H-CHO emissions at different engine speed and load conditions were tested. The conversion efficiency of a conventional diesel oxidation catalyst (DOC) in oxidizing the unregulated emissions under the World Harmonized Steady-State Cycle (WHSC) was also evaluated. The results showed that running the engine in methanol-diesel RCCI mode can significantly improve fuel economy at medium to high loads [greater than 1.18 MPa brake mean effective pressure (BMEP)]. The equivalent brake specific fuel consumption (ESFC) in the RCCI mode was lower than that of the baseline CDC mode, and the utilization of EGR can further improved fuel economy at lower load conditions. The MeOH and H-CHO emissions increased as the MSR increased, and they decreased as the load level and EGR rate increased. The CO2 emissions decreased as the MSR increased, but they increased as the EGR rate increased. The conversion efficiencies of DOC for MeOH, H-CHO and aromatic hydrocarbons (AHC) were around 93%, 84%, and 61%, respectively, under the WHSC test. Exhaust after-treatment by DOC is an effective solution to reduce unburned MeOH and H-CHO from methanol-diesel dual-fuel engines, and to extend RCCI operating range.

Comparison of direct and port injection of methanol in a RCCI engine using diesel and biodiesel as high reactivity fuels

In this work, methanol dual-direct injection (DI2 mode) was compared with the port injection of methanol (RCCI mode) when biodiesel and diesel fuel were employed as HRFs (High Reactivity Fuels). This study presents an innovative dual-direct injection strategy as an alternative method to the commonly utilized port injection strategy in RCCI engines, and evaluates its impact on both engine performance and pollutant emissions. The engine was operated at a constant speed of 2400 rpm by a single-cylinder diesel research engine, and BMEP of 1.57, 3.15, and 4.72 bar (20 %, 40 %, and 60 % of max torque) with methanol was injected using both the DI2 and RCCI modes while diesel fuel and biodiesel were injected directly. In reactivity-controlled compression ignition (RCCI) mode, NOx emissions were reduced by 60 % and 62 % for diesel fuel and biodiesel, respectively, while the reduction accounted as 92 % and 80 % in smoke opacity. However, CO and unburned HC emissions were measured as higher for advanced modes than conventional mode using diesel fuel and biodiesel. According to experimental results obtained for DI2, unburned HC and CO emissions were reduced (up to 63 % and 22 %) when compared with RCCI mode. In addition, for DI2, NOx emissions were slightly higher than in RCCI mode, mainly due to the high injection pressure (50 bar) of DI2 mode. In comparison to conventional diesel injection (CDI), cylinder pressure and heat release rate (HRR) decreased as the premixed ratio (Rp) increased at 20 % load, while cylinder pressure and HRR increased with load and Rp increased. In both diesel and biodiesel experiments, ignition delay increased as Rp increased. The ignition delay was found to be longer in RCCI mode than in DI2 mode. It was concluded that DI2 was a beneficial way to control inefficient combustion during RCCI operation fuelled by diesel fuel and biodiesel.

Comparative evaluation of combustion, performance, exergy and emission characteristics in hydrogen-biodiesel dual fuel engine under RCCI mode

The present work focuses on the impact of combustion phase shifting from CDC (conventional diesel combustion) to RCCI (reactivity controlled compression ignition) mode of operation under various premixed ratios of hydrogen on the combustion, performance and exhaust emissions of a partially modified CI (compression ignition) engine. The hydrogen premix ratios are varied from 10% to 60% with 10% increment and the engine is tested at 0.9 kW, 1.8 kW, and 2.7 kW. The experimental results have shown that the hydrogen participation up to 40% premixed ratio improves the homogeneousness and stability of the combustion, resulting in 8.19% increase in cylinder pressure and 27.81% increase in heat release rate (HRR) at 2.7 kW brake power. It is also observed that the premix phase of combustion is faster with up to 40% hydrogen participation as the 50% mass burn is found to shift towards TDC. At the same operating point, the combustion is also found to be more stable with 72% reduction in COVIMEP. The brake thermal efficiency (BTE) increases by 10.07% when operating at 2.7 kW brake power with a 40% premix ratio, compared to diesel CDC operation. The unburned hydrocarbon (UHC), carbon monoxide (CO), and PM emissions are reduced by 9.17%, 21.68%, and 9.51%, respectively, for the hydrogen premixed ratio of 40%, with a marginal increase in the oxide of nitrogen (NOX) emissions.

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

Comparative evaluation of conventional dual fuel, early pilot, and reactivity-controlled compression ignition modes in a natural gas-diesel dual-fuel engine

A Review on Recent Developments of RCCI Engines Operated with Alternative Fuels

Environmental concerns over automotive exhaust emissions and consumer demand for higher fuel efficiency have led to the development of low-temperature combustion concepts. The reactivity-controlled compression ignition (RCCI) engine is one among them and has the potential to reduce NOx and smoke emissions simultaneously. In this concept, a low-reactivity fuel is injected into the intake port and another high-reactivity fuel is injected into the cylinder directly. This results in reactivity stratification and provides more control over the rate of heat release. However, operating parameters such as reactivity of fuels, premixing ratio, injection strategies, exhaust gas recirculation ratio, piston bowl geometry, and compression ratio influence emissions formation. The article reviews recent developments on the effect of the above operating parameters on the performance and emission characteristics of RCCI engines operated with alternative fuels. The combustion strategies used to extend the RCCI mode to higher loads are also reviewed. Applications of computational fluid dynamics (CFDs) to design the combustion chamber for RCCI engines are discussed. The need for further improvements in the CFD models for RCCI engines is explained. After presenting a thorough review of recent literature, directions for future research on RCCI engines are proposed.

Numerical investigation of natural gas (NG) as low reactivity fuel in a reactivity controlled compression ignition (RCCI) engine model

Natural Gas (NG) with its high octane number and low C/H ratio is beneficial for reactivity controlled compression ignition (RCCI) engines in controlling the rate of pressure rise and lower the emissions, given that these engines still suffer from these two problems. Therefore, in this study, a detailed 3D combustion model was developed in ANSYS-Forte environment on the scanned image of a real single-cylinder diesel engine for the application of NG to RCCI engines and then validated with the experimental data of the same engine. Afterward, the effect of NG premixed ratio (Rp, 15%, 30% and 45%) on the combustion and emission characteristics of the RCCI engine were analyzed at 20% load and 2400 rpm. Results showed that by increasing the Rp, the heat release rate and cylinder pressure decreased while the ignition delay (ID) period increased. Moreover, NOx and HC emissions were observed to be increased whereas CO and C2H2 emissions tended to be declined as Rp increased. CO emissions were decreased up to 29% when RCCI mode was applied. Also, C2H2 emissions were reduced by about 97% by RCCI compared to CDM. However, engine efficiency started to decrease as Rp increased.

The influence of different fuels and injection methods of RCCI and DCI in hybrid ICE-Battery vehicle performance

The incorporation of two recent technologies of using the dual-fuel reactivity controlled compression ignition (RCCI) combustion engine within the hybrid electric vehicle (HEV) is practiced to show how this combination can reduce the emission and enhance the thermal efficiency of the system. In particular, the heat transfers from the engine wall and the exhaust heat flow from the engine under different injection modes and fuels are of interest. The study in terms of thermal performance, fuel consumption, and battery state of charge (SOC) focuses mainly on the comparison between three cases of D100 (pure diesel) as the reference (baseline conventional direct pure diesel injection) case, D80H20 (80% diesel, 20% hydrogen) direct co-injection (DCI), and D80H20 RCCI (port + direct dual fuel injection). The NOx emission and engine power in the simulated drive cycle are investigated where the battery capacity and D50M50 (direct co-injection of 50% diesel with 50% methanol) are the additional cases. The findings indicate that the Battery SOC is preserved in better condition when the RCCI mode engine is coupled in the hybrid vehicle. The piston wall heat flux for D80H20 in DCI increases by 45.2% and for the RCCI increases by 60.5% compared to baseline diesel injection mode. It is also proved that the HEV releases considerably lower NOx compared to DCI and more NOx compared to D100 and D50M50.

Effects of EGR on combustion and emission characteristics of PODE/methanol RCCI mode at high load

In order to extend the high-load operation range of polyoxymethylene dimethyl ethers (PODE)/methanol dual-fuel reactivity controlled compression ignition (RCCI) combustion mode, a numerical model of in-cylinder combustion was established by coupling PODE/methanol chemical reaction kinetics with CONVERGE software. And then the influence mechanism of exhaust gas recirculation (EGR) addition on in-cylinder combustion process, combustion stability and pollutant formation of the RCCI engine under high load and pilot injection strategy were investigated. The results show that with the increase of EGR ratio, the peak values of the first heat release formed by PODE pilot injection combustion and in-cylinder pressure decrease, the combustion start timing and CA50 phase are gradually delayed. While the peak value of the second heat release formed by PODE main injection combustion at low EGR ratio and the combustion duration remain unchanged. Meanwhile, as the EGR ratio increases from 0 to 30 %, the brake thermal efficiency (BTE) decreases from 46.54 % to 44.40 %. And the in-cylinder equivalent ratio and temperature field distributions become uniform, and both high-temperature region (above 1800 K) and NOx generation area are reduced, which decreases NOx emissions by 42.6 % without increasing soot emissions. The methanol mixture at squish zone is subjected to the high-temperature and high-pressure of pilot injection combustion, resulting in obvious pressure oscillation. While EGR addition decreases the generation of HCO and OH active radicals, ignition points and reaction rate, which effectively inhibits methanol spontaneous combustion and knock phenomenon, and decreases the ringing intensity from 2.82 MW/m2 to 1.50 MW/m2. The pilot injection strategy coupled with 18 % EGR can extend the indicated mean effective pressure to 1.22 MPa. However, the load further extension is mainly limited by the sharp decline of BTE.

Effect of pilot injection strategy on the methanol-mineral diesel fueled reactivity controlled compression ignition combustion engine

Amongst all low-temperature combustion (LTC) strategies, reactivity-controlled compression ignition (RCCI) combustion garners more debate from researchers because of its excellent combustion and performance characteristics and lower emissions over a wide operating range. In this experimental investigation, the consequences of the start of diesel injection (SoIdiesel) timing using different pilot injection techniques, such as single and double pilot injection (SPI and DPI, respectively), have been investigated. Tests were performed at a fixed engine speed and load (1500 rpm and 3 bar BMEP, respectively) using different premixed ratios (rp: 0, 0.25, 0.50, and 0.75) of methanol on an energy basis. Experimental results indicated that the start of combustion (SoC) and combustion phasing (CP) advanced with advancing SoIdiesel. However, too advanced and retarded SoIdiesel timings resulted in combustion noise and misfire. The use of pilot injection was found suitable for the RCCI mode, especially at lower rp. However, SPI and DPI strategies didn’t show significant variations in the combustion characteristics. Exhaust gas temperature (EGT) showed a random trend with SoIdiesel timing, and it decreased with the increasing number of pilot injections. RCCI mode produced higher hydrocarbon (HC) and carbon monoxide (CO) and lower oxides of nitrogen (NOx) emissions. All these gaseous emissions decreased with advancing the SoIdiesel. Particulate matter (PM) analysis showed that the RCCI mode emitted relatively lower PM than the baseline CI mode, further reducing with increased methanol fuelling. PM emissions also decreased by retarding SoIdiesel, in which reduction in smaller particles was dominant. The analysis of critical parameters such as brake thermal efficiency (BTE), HC, NOx, and PM emissions suggested that the optimum rp of methanol and suitable injection strategy can significantly improve the combustion, performance, and emissions characteristics of the RCCI mode.