Reactivity Controlled Compression Ignition Operation Research Articles

Enhancing the usability range of acetylene in CI engines through split injection of high-reactive fuel under RCCI operation: Optimized operability using an MCDM approach

Reactivity Controlled Compression Ignition (RCCI) has emerged as a promising solution to address the challenges of advanced combustion techniques in diesel engines, balancing combustion control and emission reduction. This study investigates the impact of split-injection high-reactivity fuel (HRF) dosing in RCCI to enhance charge homogeneity at lower injection timing advancements. It systematically explores progressive advancements in HRF injection timing, distinguishing between main and pilot injections. The main injection varied from 20° bTDC to 70° bTDC, while the pilot injection, relative to the main injection, spans 25°-40° CA ahead with a 5° progression. As an LRF, Port-injected Acetylene supplements the process with variable premixed ratios. Further, using a multi-criteria decision-making method (AHP), the study optimizes operating conditions, proposing a main injection at 20° bTDC, a pilot injection 40° CA ahead, and 70 % LRF participation. This optimized condition yields significant benefits such as 32.99 % higher brake thermal efficiency (BTE), 160 % longer premixed duration, 18.65 % lower maximum temperature, 89.41 % lower NO emissions, 91.83 % lower hydrocarbon (HC) emissions, 91.24 % lower CO emissions and 97.20 % lower smoke opacity compared to conventional diesel combustion (CDC) operation. The results highlight the advantages of multiple fuel injections in RCCI, improving blending characteristics at lower injection angles.

Adoptability assessment of HCDI and RCCI modes in plug-in parallel hybrid electric vehicles using sustainable fuels and model-based torque structure calibration strategies

In this research, a comparative analysis of plug-in hybrid electric vehicle (PHEV) engine was conducted with two advanced low temperature combustion (LTC) techniques viz. Homogeneous charge with direct injection (HCDI) and reactivity-controlled compression ignition (RCCI), utilizing alternative fuels diethyl ether (DEE) and ethanol. This was attempted to exhibit the promising potential of LTC based PHEV to achieve the highest efficiency and low emissions. The experimental results disclosed that DEE powered HCDI can achieve superior thermal efficiency with an impressive peak torque of 14 Nm. On the other hand, ethanol powered RCCI produced a peak torque of 17.5 Nm with remarkable emission reduction characteristics, especially CO2. It was vindicated that HCDI-PHEV outperformed the RCCI-PHEV in terms of fuel economy despite both HCDI and RCCI being lower than the conventional diesel PHEV. The NOx emissions from HCDI were almost negligible. About 20 % lower nitrogen oxide (NOx) emissions were recorded for RCCI respectively as compared to diesel (36 g/s). HCDI and RCCI showcased about 2 and 1.3 times higher soot emissions than diesel (7.12 g/s). Fuel economy was improved by 15 % and 43 % respectively under HCDI and RCCI modes over the conventional diesel mode of PHEV operation. When the PHEV was operated continuously for about 3.5 h, the battery's SOC dropped from 80 % to 45 % under diesel operation, whereas it only reached 50 % and 60 % under RCCI and HCDI mode operation. Low fuel consumption characteristics, acceptable torque production capabilities and ultralow NOx reduction potential established HCDI as the preferable choice for PHEV over RCCI.

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

Impact of engine control variables on low load combustion efficiency and exhaust emissions of a methane-diesel dual fuel engine

A conventional diesel engine when operated in the reactivity-controlled compression ignition (RCCI) combustion strategy faces challenges of high total hydrocarbon (THC) and carbon monoxide (CO) emissions leading to poor combustion efficiency at low engine loads. The oxides of nitrogen (NOx) versus smoke trade-off, encountered in conventional diesel combustion, is replaced by the NOx-THC trade-off in the RCCI operation. This work focuses on addressing the NOx-THC trade-off issue by systematically investigating the effects of engine control variables, such as, fuel injection timing, exhaust gas recirculation (EGR) and intake throttling, on a light duty compression ignition engine running in a methane-diesel dual fuel mode. The engine is operated at a load of 3 bar gross indicated mean effective pressure and at a speed of 1500 rev/min. Based on relationships identified between engine control variables, combustion parameters, emissions and engine performance, a bottom-up approach is used to combine the control variables synergistically to improve the NOx-THC trade-off. A combination of advanced start of injection timing of diesel (−35 degree crank angle (°CA) after top dead centre), 50% premix ratio and 55% EGR levels along with the end of port fuel injection of methane in the middle of the intake stroke (−270°CA), has resulted in a ∼34 percentage points (from 56% to 90%) improvement in combustion efficiency and a ∼9.5 percentage points improvement in thermal efficiency compared to the baseline low load dual fuel operation while maintaining good combustion stability. THC emission is reduced from 105 to ∼25 g/kWh whilst maintaining low levels of NOx (<0.3 g/kWh).

Comparative analysis of waste tire pyrolysis oil and gasoline as low reactivity fuel in RCCI engine

ABSTRACT The utilization of alternative fuels in internal combustion engines has gained significant attention due to concerns about energy security and environmental sustainability. Waste tire pyrolysis oil (WTPO) is a potential alternative fuel that can be produced from waste vehicle tires through a pyrolysis process. In this study, the possible use of WTPO in a diesel engine operating under Reactivity Controlled Compression Ignition (RCCI) mode was investigated. In the study, the use of WTPO as a low-reactivity fuel in RCCI engines is examined, highlighting the importance of innovative approaches to alternative fuels with varying reactivity levels for effective combustion control and emission reduction. In the experimental work, WTPO was tested at different energy rates of 15%, 30%, and 45% into the intake port using the PFI system, while conventional diesel fuel was injected directly into the cylinder by the CRDI system. The tests were carried out under different engine load conditions while maintaining a constant engine speed of 2400 rpm. The performance, combustion, and emission characteristics of the engine were analyzed and compared between WTPO and conventional gasoline fuel as LRF. The study results show that using WTPO in RCCI operation with sustainable ringing intensity leads to significant increases in Brake Thermal Efficiency (BTE) compared to gasoline usage, with BTE increments of up to 5%, 3.3%, and 6.3% observed with increasing engine load. Furthermore, WTPO usage in RCCI engines effectively reduced hydrocarbon (HC) emissions, addressing a significant issue, and maintaining the known benefits of reactivity-controlled combustion. These findings suggest that WTPO can be utilized as a viable low-reactivity fuel in RCCI engines with acceptable performance, combustion, and emission characteristics.

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.

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.

Effects of piston shape and nozzle specifications on part-load operation of natural gas–diesel dual-fuel RCCI engine and its application to high load extension

• Effects of piston shape and multi-angle nozzle were evaluated for DF RCCI operation. • Enhanced air utilization w/multi-angle nozzle reduced combustion and HT losses. • The highest GIE of RCCI improved as 51.8 % by hardware modifications. • Intake air amount could be increased by lowering CR (from 17 to 15) at the maximum load. • The maximum load of RCCI could be extended from 81 (reference) to 101 kW of BP. In this study, the effects of modifications of both the piston shape and injector nozzle are experimentally investigated for high load extension of a natural gas–diesel dual-fuel reactivity-controlled compression ignition (RCCI) engine. First, a bathtub shape with a reduced compression ratio is applied to the modified piston which was reported to improve the flame propagation in squish volume, the cooling loss, and the air induction rate under the same limit of in-cylinder pressure from previous studies. In addition, a multiangle two-layer injector is used to extend the maximum load, which has been proven to be effective for unburned hydrocarbon emissions and gross indicated efficiency in part-load operation in our previous study. The experiments are conducted under both 1200 rpm part-load operation (approximately 1950 J/cylinder per cycle of fuel input energy) and 1800 rpm maximum load operation. The objectives are to comprehensively evaluate the effects of the modifications on natural gas–diesel RCCI operation and verify the effects of all load conditions. The experimental results reveal that the changes in the piston—reduction in the compression ratio and a bathtub piston shape—are effective for both NOx and smoke emissions as the diesel injection timing is advanced. Although the multi-hole double layer (combined narrow and wide injection) has less effect on emissions compared to that of the change in piston, it affects the mixing process inside the cylinder, thus retarding the combustion phasing, prolonging the combustion duration, and eventually reducing the cooling loss. Both modifications are highly effective for advanced diesel injection timing corresponding to RCCI operation, which extends high-load operation from 80.9 to 101 kW of brake power, relatively 24.8 % increase, by adopting both the piston and injector modifications. Based on the modifications, the mass fraction of natural gas is suggested to be approximately 80 %. A higher fraction causes the variation in the maximum in-cylinder pressure to be extremely sensitive to allow robust operation. In contrast, if it is lower, the amounts of both NOx and smoke emissions exceed the emission standard levels (0.4 g/kWh and 15 mg/kWh for NOx and smoke emissions, respectively, corresponding to Stage-V of non-road engine operation).

Machine Learning-based Classification of Combustion Events in an RCCI Engine Using Heat Release Rate Shapes

Reactivity controlled compression ignition (RCCI) mode offers high thermal efficiency and low nitrogen oxides (NOx) and soot emissions. However, high cyclic variability at low engine load and high pressure rise rates at high loads limit RCCI operation. Therefore, it is important to control the combustion event in an RCCI engines to prevent abnormal engine combustion. To this end, combustion in RCCI mode was studied by analyzing the heat release rates calculated from the in-cylinder pressure data at 798 different operating conditions. Five distinct heat release shapes are identified. These different heat release traces were characterized based on start of combustion, burn duration, combustion phasing, maximum pressure rise rate, maximum amount of heat release, maximum in-cylinder gas temperature and pressure. Both supervised and unsupervised machine learning approaches are used to classify different types of heat release rates. K-means clustering, an unsupervised algorithm, could not cluster the heat release traces distinctly. Convolution neural network (CNN) and decision trees, supervised classification algorithms, were designed to classify the heat release rates. The CNN algorithm showed 70% accuracy in predicting the shapes of heat release rates while decision tree resulted in 74.5% accuracy in predicting different heat release rate traces.

Comparative experimental analysis on dual fuel with biodiesel-acetylene in reactivity controlled compression ignition engine

ABSTRACT In the latest Compression Ignition (CI) engines, a gaseous fuel plays a significant role because they have the advantage of a low knock-creating tendency and lower carbon emissions. In B20 Mahua Oil Methyl Ester (MOME)-acetylene dual-fuel Reactivity Controlled Compression Ignition (RCCI) engines, an effort has been made to use gaseous fuel acetylene as a Low Reactivity Fuel (LRF). RCCI engines are well known for their low particulate matter and Nitrogen Oxides (NOx). In the current study, all the aforementioned technologies are concurrently used to attain better performance, emission and combustion characteristics. The test engine is properly modified to allow acetylene to be injected at an angle of 60° to stimulate better turbulence intake air at different flow rates, from 1 to 5 litres per minute (LPM). The result shows an increase in acetylene mass flow rates, increases the Brake Thermal Efficiency (BTE) for B20 MOME. A maximum BTE of 32.6% is achieved at the RCCI B20 MOME-acetylene operation with acetylene flow rate of 4 LPM, which is marginally lower with Conventional Diesel Engine (CDE) operation. In B20 MOME- 4 LPM Acetylene RCCI operation, the NOx emission, the smoke density, Hydro Carbon (HC) and Carbon Monoxide (CO) are reduced by 11.8%, 10.4%, 5.3% and 14.3%, respectively compared to B20 MOME in CDE operation.

An experimental investigation on gasoline diesel and biofuelled RCCI combustion and its comparison with the conventional diesel combustion

Amongst all the low temperature combustion (LTC) strategies, reactivity controlled compression ignition (RCCI) is the most promising one due to their control on combustion pashing and heat release rate (HRR). This experimentation investigates the emission, performance and combustion characteristics of the modified constant speed non road single cylinder RCCI engine and its comparison with the conventional diesel engine. In RCCI operation, gasoline and blends of ethanol and gasoline, E10 and E20 were used as a low reactivity fuel (LRF), while diesel and blends of diesel and jatropha biodiesel, B10, B20 were used as a high reactivity fuel (HRF). The ratio of LRF and HRF maintained about 60:40. For RCCI operation, 10% hot exhaust gas recirculation (EGR), Injection pressure, 3 bar for PFI (port fuel injection) pressure, and 500 bar for HRF were used. Experimentation was carried out for 1500 rpm and 0, 4, 8 and 12 kg loading conditions. From experimental results, it has been concluded that, in comparison with the conventional diesel engine, for 12 kg loading condition, there was a 92% reduction in the NOx and 72% reduction in smoke opacity observed as an effect of reduction in combustion chamber temperature for E20-B20 blend. Compared to conventional diesel, there was an 11% rise in the brake thermal efficiency for the E10B10 fuel combination. As combined effects of NOx, Smoke opacity, and brake thermal efficiency are concerned, E10-B10 is the suitable combination for given operating conditions.

An optical investigation of dual fuel and RCCI pilot ignition in a medium speed engine

Driven by the Paris agreement and tightening IMO regulations, the marine sector is focusing on lowering engine emissions and moving to low-carbon fossil or renewable fuel such as methane. The dual-fuel concept allows the usage of methane as main energy-source in diesel engines. A small pilot diesel injection acts as an ignition source for the premixed methane. It was investigated how NOx formation, mainly taking place during combustion of the pilot fuel, could be minimized.To better understand the process of ignition of a pilot injection in dual-fuel engines, optical research has been performed on a medium speed dual fuel marine engine. A unique Bowditch 200 mm single cylinder setup enabled high speed recordings of natural luminescence. Both Reactivity Controlled Compression Ignition (RCCI) and Conventional Dual Fuel (CDF) combustion was investigated. The RCCI combustion was created by an early pilot injection, allowing a long mixing time. The CDF cases had a late injection timing.In RCCI operation the higher degree of premixing was recognized by combustion luminescence starting further away from the injector, at a varying location. The diluted pilot combustion generated a limited brightness. The heat release profile was Gaussian/bell-shaped, without the typical diesel premixed peak. In CDF operation the recorded images show that combustion follows the shape of the diesel injector jet. The heat release profile was showing a strong initial peak, resembling the premixed peak known from conventional diesel combustion. This heat release peak in CDF combustion, correlated to NOx emissions, is absent in RCCI mode.

Design, development and testing a hybrid control model for RCCI engine using double Wiebe function and random forest machine learning

Reactivity controlled compression ignition (RCCI) engine technology significantly reduces emissions of NOx and soot while improving thermal efficiency. RCCI engine development requires optimum in-cylinder combustion metrics as desired objective across different operating conditions. Physics-inspired control models are a cost-competitive option to achieve these objectives in engine control systems. Combining these control models with machine learning can offer computational efficiency, higher accuracy and lower number of experiments needed for control system calibration. In this context, the present paper proposed a novel hybrid control model by combining physics-inspired parametrized double Wiebe function (D-W) and Random Forest Machine Learning (RFML) to predict both the average and cyclic variation trends of combustion metrics in an RCCI engine. In this work, firstly, an optimized D-W parameters matrix was formulated that can stochastically reconstruct pressure cycles in agreement with 99.7% of the experimental confidence interval. RFML was then employed to develop correlative learning models between experimental control variables such as premix ratio, engine load, injection timing etc. with corresponding D-W parameters matrix. The hybrid control model was used to predict peak pressure (PP), indicated mean effective pressure (IMEP), crank angle for 50% of fuel mass fraction burnt (θ50) and maximum pressure rise rate (MPRR) across 60 test cases and 36000 cycles. Results showed an error mean and standard deviation (μerr±σerr) of 0.068 ± 1.840 bar, 0.007 ± 0.264 bar, 0.15 ± 0.98° CA and 0.018 ± 0.221 bar/° CA between predictions and experiment for PP, IMEP, θ50 and MPRR, respectively in the tenable RCCI operation regime. Proposed hybrid control model exhibited good accuracy and was able to capture the local cyclic variation trends.

An innovative research on variable compression ratio in RCCI strategy on a power generator diesel engine using CNG-safflower biodiesel

The CNG usage as a fuel in IC engines have many advantages such as decreasing CO2 and PM and smoke emissions and in many cases reducing NOx emission, along with its low prices and naturally abundance spread on the world. In heavy loaded operation of diesel engines, it becomes very hard to control excessive NOx, and PM formation in the exhaust emissions and smoke accumulation especially for biodiesel usage. In the present study, in order to achieve the usability of higher percentages of biodiesel with CNG, the low temperature combustion of reactivity controlled compression ignition (RCCI) strategy have been applied in a single cylinder diesel engine with variable compression ratios. The CNG, as the low reactivity fuel, was subjected to the intake manifold as the substitute the gas with 5%, 10% and 15% of biodiesel under 1500 rpm and 10.8 kW(full load) load of the engine with variable compression ratios from 13:1 to 19:1 in order to investigate the effects of compression ratios on RCCI operation with high percentages of biodiesel and CNG usage. Apart from the main performance, emissions and combustion indicators of diesel engines tests, 3 novel parameters (SPE, STE and SHRE) were created for the first time in order to deeply evaluate the combustion. Mean of cylinder pressure was increased while combustion duration was lowered for CNG usage with biodiesel. BTE was increased while BSEC and BSFC were decreased in either operation of biodiesel/CNG RCCI and various CR. In addition, NOx emissions were lowered for CNG usage and CR decrease, along with smoke decrease for biodiesel/CNG RCCI combustion.

Exploring the effects of diesel start of injection and water-in-ethanol concentration on a reactivity controlled compression ignition engine

Wet ethanol applications in compression ignition engines may become important in the coming years due to the possibility of replacing a fossil fuel by a renewable one, with low production cost and accessible production in remote regions. In this context, this research sought to explore the use of renewable fuel and its potential for operation in an engine with reactivity-controlled compression ignition (RCCI) combustion. Ricardo single-cylinder research engine was used. Fuel direct injection into the cylinder was performed in just one step, and to make possible the RCCI operation, the following parameters were varied: water-in-ethanol concentration, ethanol port fuel injection duration, and the start of injection (SOI) crank angle. By varying these parameters, it was possible to explore 38 different test conditions in dual-fuel mode and 2 baseline tests. Operations in RCCI were only possible over 74% replacement, with advanced SOI (333° and 326°). Diesel replacement reached 86% (mass basis). However, the results did not demonstrate a significant increase in indicated thermal efficiency. Furthermore, only with the highest water-in-ethanol concentrations, the engine operated stably at SOI of 326°. For similar replacements, the advancement of SOI has reduced CO emissions, while NOx emissions have increased.

Experimental Assessment of Effects of n-Butanol on Performance, Emission, and Combustion Characteristics of Mahua Oil Fueled Reactivity Controlled Compression Ignition (RCCI) Engine

The emission and combustion characteristics of diesel engine operated under reactivity controlled compression ignition (RCCI) mode are investigated in this study. A separate electronic fuel injector was mounted on the intake manifold of the engine meant for RCCI operation. RCCI mode of operation was conducted by injecting “n-butanol” as low reactivity fuel into the intake, and “mahua oil” as high reactivity fuel directly into the combustion chamber. Experimental results reported that smoke and nitric oxide (NO) emissions are significantly reduced by 45.4% and 33.1% through RCCI mode when compared with single fuel mode (mahua oil) at peak load. Carbon monoxide (CO) and unburnt hydrocarbon (HC) emissions were substantially increased at part load conditions in RCCI mode by increasing n-butanol energy share, while both HC and CO emissions were reduced at maximum power output. About 6.2% increase in brake thermal efficiency (BTE) of the engine was found when operated in RCCI mode, with up to 20% of n-butanol share; beyond this energy share, a marginal drop in BTE was noted at peak load. A substantial rise in cylinder pressure and heat release rate (HRR) was found while operating in RCCI mode. At part load, ignition delay was found to be longer in RCCI operation, but at supreme load condition, it was reduced. It was concluded that RCCI mode of operation improved the engine’s performance and similarly reduced smoke and NO emissions.

Frequency Response Based Multivariable Feedback Control Design for Transient RCCI Engine Operation

Reactivity Controlled Compression Ignition (RCCI) is a high efficient, pre-mixed combustion concept, which is characterized by controlled auto-ignition. RCCI control has to guarantee stable and safe operation for varying operating conditions. Research concentrated on next-cycle fuel path control, so far. However, a crucial step towards on-road implementation is accurate control of both air and fuel path, especially during transients. In this work, a systematic, frequency domain-based design method is presented for coordinated air-fuel path control. Starting from MIMO system identification using Frequency Response Functions, cylinder individual combustion models are developed. Based on these models, a static decoupling matrix and five SISO PI controllers are designed. The followed method allows to analyze and guarantee local robust stability, disturbance rejection and reference tracking properties. For transients, the controller is scheduled as a function of engine speed and torque. The potential of the designed MIMO controller is demonstrated on a six-cylinder Diesel-E85 RCCI engine. This controller shows good reference tracking for engine speed-load variations. Furthermore, it enables safe RCCI operation towards higher loads compared to open-loop control strategies.

Effects of direct-injection fuel types and proportion on late-injection reactivity controlled compression ignition

The late-injection strategy can decrease peak pressure rise rate (PRR) in reactivity controlled compression ignition (RCCI) and enables RCCI operation to high engine load. However, excessive soot emission is a limiting factor in this high engine load extension. Recently, polyoxymethylene dimethyl ethers (PODE) emerges as a promising direct-injection fuel for RCCI load extension due to the properties of high reactivity and high oxygen content. The late-injection RCCI strategy features a two-stage high-temperature heat release (HTHR) that has not been well understood. In this study, we investigated the effects of direct-injection fuel properties types and proportion on late-injection RCCI strategy on a light-duty optical engine using multiple optical diagnostic techniques. Iso-octane served as the premixed fuel and the in-cylinder direct-injection timing was set at the crank angle of −10° after the top dead center. Firstly, the combustion characteristics of RCCI with direct-injection fuels of n-heptane, PODE and cetane were compared. The NFL images prove that the PODE case shows less tendency of soot formation. The OH planar laser-induced fluorescence (PLIF) imaging indicates that the OH radical is widely distributed in the combustion chamber after the HTHR including the central part of the combustion chamber near the injector nozzle for all three cases. Secondly, the effects of direct-injection fuel proportion on the combustion characteristics of the late-injection RCCI strategy was evaluated using PODE as the direct-injection fuel. The NFL images show that the combustion regime in the low reactivity region of RCCI tends to change from auto-ignition to flame front propagation with the decreasing of the direct-injection fuel proportion from 30% to 6%. The introduction of the flame front propagation in the second-stage HTHR reduces the peak pressure rise rate of RCCI. We conclude that the peak PRR of RCCI at high engine load can be controlled by modulating the ratio between the auto-ignition and flame front propagation through tuning the proportion of the high-reactivity fuel in the direct injection.

Reactivity Controlled Compression Ignition combustion and emissions using n-butanol and methyl oleate

Direct Injection of methyl oleate and PFI of n-butanol were used to conduct Reactivity Controlled Compression Ignition (RCCI) and minimize exhaust emissions in reference to conventional diesel combustion. Methyl oleate was investigated for validation of a single fatty acid methyl ester as a surrogate for biodiesel in engine operation. An experimental common rail engine was operated in RCCI and conventional diesel combustion modes under constant boost and similar combustion phasing. The RCCI strategy used two pulses of direct injections with a fixed first injection at 60° before top dead center and a varied second injection for smooth combustion. Ringing intensity was reduced by 70% for methyl oleate RCCI compared to diesel conventional diesel combustion. The molecular oxygen from methyl oleate allowed a reduction in soot by 75% and 25% compared to diesel in RCCI and conventional diesel combustion operation, respectively. Compared to conventional diesel combustion, NOx and soot decreased for RCCI by several orders of magnitude with both emissions approaching near zero levels at low load. The fuels produced a stable RCCI operation where mechanical efficiency was sustained within 2% for same-load points and the coefficient of variation of indicated mean effective pressure was limited to 2.5%.