Compression Ignition Combustion Research Articles

Impacts of pine oil and hydrogen induction with hemp oil methyl ester on dual fuel reactivity controlled compression ignition combustion in diesel engine

AbstractThe current research focuses on the impacts of pine oil injection and hydrogen induction separately with hemp oil methyl ester (HOME) in the single cylinder diesel engine in dual fuel‐reactivity controlled compression ignition (DF‐RCCI) combustion mode. The engine was tested under a DF‐RCCI mode for the different energy shares of 10% pine oil with HOME (10P‐HOME), 30% pine oil with HOME (30P‐HOME), 3‐lpm hydrogen with HOME (3‐lpmH2‐HOME), and 6‐lpm hydrogen with HOME (6‐lpmH2‐HOME) separately at 345 °CA bTDC of low reactivity fuel (pine oil and hydrogen) and 23°C bTDC injection timing of high reactivity fuel (HOME). The results showed a higher Brake Thermal Efficiency (BTE) of 7.44%, 5.32%, 5.72%, and 2.46% for 6‐lpmH2‐HOME, 3‐lpmH2‐HOME, 30P‐HOME, and 10P‐HOME fuel shares, respectively, over the conventional diesel combustion (CDC) at full load. 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME fuel combinations recorded 4.08% 4.42%, and 5.69% lower brake specific fuel consumption (BSFC), respectively, at full load. When comparing DF‐RCCI combustion to CDC, an increase in the heat release rate (HRR) of 2.89%–26.50% and a rise in peak cylinder pressure of 0.77%–12.99% were observed. The 30P‐HOME, 3‐lpmH2‐HOME, and 6‐lpmH2‐HOME emit less smoke in DF‐RCCI combustion mode by 13.06%, 4.84%, and 7.26%, respectively at full load condition. When using 30P‐HOME the exhaust gas temperature (EGT) decreased by 3.50% at full load condition. At part and full load conditions, the 30P‐HOME fuel share reduced oxides of nitrogen (NOX) emissions by 3.93% and 5.26%, respectively.

Laboratory Tests of Electrical Parameters of the Start-Up Process of Single-Cylinder Diesel Engines

Despite continuous work on new power systems for vehicles, machines, and devices, the combustion engine is still the dominant system. The operation of the combustion engine is initiated during the starting process using starting devices. The most common starting system used is the electric starter. The starting process of an internal combustion engine depends on the following factors: the technical condition of the starting system, technical condition of the engine, battery charge level, lubricating properties, engine standstill time, engine and ambient temperature, type of fuel, etc. This article presents the results of laboratory tests of the electrical parameters of the starting process of a single-cylinder compression–ignition engine with variable fuel injection parameters and ambient temperature conditions. It was confirmed that for the increased fuel dose FD2, higher values of the measured electrical parameters (Imax, Pmax, and Pmed) were obtained compared to the series of tests with the nominal fuel dose. Knowledge of the values of the electrical parameters of the starting process is important not only for the user (vehicle driver, agricultural machinery operator, etc.), but above all for designers of modern starting systems for combustion engines and service personnel. The obtained results of testing the electrical parameters of the combustion engine during start-up may be helpful in designing new drive systems supported by a compression–ignition combustion engine.

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.

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

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

Combining Gasoline Compression Ignition and Powertrain Hybridization for Long-Haul Applications

Gasoline compression ignition (GCI) combustion was demonstrated to be an effective combustion concept to achieve high brake thermal efficiency with low-reactivity fuels while offering improved NOx–soot trade-off. Nevertheless, future greenhouse gas regulations still challenge the heavy-duty transportation sector on both engine and vehicle basis. Hybridization is a possible solution in this scenario, allowing the avoidance of low-efficiency conditions and energy recovery during regenerative braking, improving overall vehicle efficiency. In this sense, this investigation proposes a detailed analysis to understand the optimum hybridization strategy to be used together with GCI to simultaneously harness low pollutant and CO2 emissions. For that, different hybrid architectures were defined in GT Drive (Mild hybrid 48 V P0 and P2 and full Hybrid P2 500 V) and submitted to 15 different use cases, constituted by five normative and real-driving conditions from the US, China, India, and Europe and three different payloads. Results showed that all hybridization strategies could provide fuel savings benefits to some extent. Nonetheless, usage profile is a dominant factor to be accounted for, benefiting specific hybrid powertrains. For instance, P0 and P2 48 V could provide similar savings as P2 500 V, where regenerative braking is limited. Nonetheless, P2 500 V is a superior powertrain if more demanding cycles are considered, allowing it to drive and recuperate energy without exceeding the Crate limitations of the battery.

Effects of Varying Equivalence Ratios on the Combustion Efficiency Characteristic of a Dual-Fuel Compression Ignition Engine by Changing Intake Pressures and Exhaust Gas Recirculation Rates

In general, a leaner mixture condition improves combustion efficiency in compression ignition (CI) combustion using diesel. However, in the case of leaner air–fuel mixture conditions, it disturbs flame propagation in spark ignition combustion using gasoline, i.e., low reactivity fuel, causing a decrease in combustion efficiency. Since dual-fuel combustion in a CI engine typically involves the use of high- and low-reactivity fuels together, the differing reactivity conditions in the cylinder become as important as the local equivalence ratio in the cylinder. Thus, there is a need to verify the effect of a leaner mixture condition on combustion efficiency in dual-fuel CI combustion. For this reason, this study experimentally evaluates the effects of varying equivalence ratios on the combustion efficiency of gasoline/diesel dual-fueled CI combustion in a 0.4-L single-cylinder engine under low-speed (1500 rpm) and low-load (total LHV 570 J/str) conditions. To vary the equivalence ratios, intake pressures and exhaust gas recirculation (EGR) rates were, respectively, changed under the part-load condition. The results emphasize that as the equivalence ratio becomes leaner by increasing the intake pressure, combustion efficiency worsens due to the low reactivity properties and certain flame propagation modes of gasoline combustion. On the contrary, increasing the EGR rate did not significantly influence combustion efficiency, but it effectively helped reduce nitrogen oxide (NOx) emissions. Based on these results, it is concluded that optimizing dual-fuel CI combustion to suppress NOx emissions is better achieved using EGR, rather than creating a leaner mixture condition.

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

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

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

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

Potential of 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP) to enhance the cetane number of ethanol, a detailed chemical kinetic study

Ethanol is one of the most promising renewable liquid fuels to decarbonize the internal combustion engine due to its high production capacity, reasonable cost and low carbon intensity. At the same time, diesel engines are preferred over other powertrain technologies in most hard-to-electrify applications, such as heavy-duty, off-road, marine and rail. However, ethanol’s properties are not suitable for modern diesel engines with ignitability being the main technical barrier for ethanol compression-ignition combustion. Cetane improvers, such as 2-ethylhexyl nitrate (EHN) or di-tert-butyl peroxide (DTBP) may be a solution to enable diesel-like ethanol combustion, but the potential of those additives to increase the cetane number of ethanol is still unclear.In this investigation, detailed chemical kinetic simulations were performed to better understand the mechanisms by which EHN and DTBP affect the ignition reactivity of ethanol. Sub-models of EHN and DTBP chemistry were merged with a chemical kinetic mechanism for ethanol and validated against experimental data. Rate of production analyses and sensitivity analyses were performed to better understand the reactions and species that control the autoignition of ethanol additized with EHN or DTBP. The formation and accumulation of acetaldehyde from ethanol-derived radicals is the bottleneck for ignition, since the remaining ethanol acts as a sink of the OH radicals required for the decomposition of acetaldehyde. A simple model to predict the derived cetane number of fuel blends is proposed and used to estimate the effectiveness of EHN and DTBP in improving the reactivity of ethanol. EHN works better as an additive as compared to DTBP, as it speeds up the main decomposition reactions of the fuel by providing the necessary OH radicals as compared to CH3 provided by DTBP.

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

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

Combustion noise characterization and optimization of PCCI combustion using response surface methodology

The current work aims at characterizing the premixed charge compression ignition (PCCI) combustion with regression-based approach using response surface methodology. PCCI operating parameters such as load, pilot injection timing, main injection timing, pilot injection quantity, exhaust gas recirculation and injection pressure are considered as input variables. Engine performance indicators such as brake thermal efficiency, brake specific fuel consumption, carbon monoxide (CO), hydrocarbon (HC), oxide of nitrogen (NOx), smoke emissions, combustion phasing and combustion noise metric ringing intensity are considered as output responses. Experimental results validate the optimal solution from response surface methodology approach, and good agreement is found between mathematical models and experimental results. Comparative examination of optimized PCCI combustion versus conventional combustion showed a 66% and 44% decrement in NOx and smoke emissions. Except for CO and HC emissions, the percentage penalty of other responses with PCCI combustion is less than 10%. In addition to ringing intensity another combustion noise metric combustion noise level is computed from Fast Fourier Transform (FFT) analysis of cylinder pressure trace. A combustion noise level of 73.26 dB is obtained at optimized conditions.

Study on the Effect of Coupled Internal and External EGR on Homogeneous Charge Compression Ignition under High Pressure Rise Rate

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency.

A Numerical Investigation on Laminar Flame Speed of Syngas in Air with Ozone Addition

In the context of energy and propulsion systems, in recent years engineering research has increased its efforts to develop more efficient technologies with a lower environmental impact. Specifically, new combustion systems have been investigated, such as ultra-lean combustion and Homogeneous Charge Compression Ignition (HCCI) combustion, and sustainable fuels have been employed. With respect to the latter option, syngas and hydrogen have emerged as attractive choices. However, the low specific energy of syngas and the presence of diluents can cause flame failure and instability. On the other hand, it is well known that ozone-assisted combustion enhances the Laminar Flame Speed (LFS), reduces the ignition delay time, and improves the flame stabilization of fuels such as methane, n-heptane and iso-octane, since it affects the chemistry in the Low Temperature Combustion (LTC) regime. In this context, the aim of the present work is to evaluate the effect of ozone on the LFS of syngas/ozone/air mixtures. Specifically, 1-D simulations have been carried out to compute the LFS of CO/H2 and CO/H2/N2 syngas mixtures. The model has been validated against experimental data available in the scientific literature by considering four different reaction mechanisms. Then, the model has been used to perform a parametric analysis by considering different conditions in terms of syngas composition (three different CO/H2 ratios) and equivalence ratio (from 0.5 to 5). The results show that the addition of 2500 ppm of ozone in air results in an increase in LFS for all equivalence ratios examined. The four different mechanisms give comparable results in terms of LFS and LFS increase for CO/H2 syngas, and are also able to predict ozone effect on LFS enhancement for CO/H2/N2 mixtures. Finally, the results show that the influence of ozone, in terms of LFS percentage increase, is greater for CO/H2 ultra lean mixtures with a lower CO/H2 ratio.

Effects of using a novel fuel vaporizer on partially premixed charge compression ignition (PPCCI) engine emissions, performance, and combustion characteristics

Environmental concerns of toxic emissions and depleting of fossil fuel supplies due to their excessive usage as the main source of energy have raised interests in the creation of novel combustion modes that result in reduction of combustion temperatures and produce low emissions. In comparison to conventional diesel engines, the partially pre-mixed charged compression ignition (PPCCI) combustion strategy has demonstrated its ability to significantly reduce emissions carbon monoxide (CO), unburned hydrocarbon (HC), oxides of nitrogen (NOX), carbon dioxide (CO2) and smoke opacity. In order to compare the results with those of conventional engines, the current experimental work’s objective is to investigate the combustion, performance, and exhaust emissions characteristics of PPCCI engines. A single-cylinder, air-cooled, 4-stroke, direct-injection diesel engine that had been modified to run in PPCCI mode was used for the experiments. An external mixture formation technique with a fuel vaporizer is added to create the homogeneous mixture for PPCCI combustion. After being heated to the point of vaporization, liquid diesel fuel vapor was mixed with some fresh air and then the mixture directed to the intake manifold, where it was mixed with the remaining fresh air to create an external homogenous mixture that filled the combustion chamber. The tests were conducted at different premixed ratios of diesel fuel proportions of 15%, 20%, and 30% in the intake port. However, the fuel vaporizer chamber was kept at fixed temperature of 100 °C, 105 °C, 110 °C, 115 °C, and 120 °C. The PPCCI engine results were compared with the conventional engine data. Results from the PCCI technique at various premixed ratios indicate a certain decrement for HC, CO, NOX, and smoke emissions, rising in BTE “brake thermal efficiency”. At 30% premixed ratio of the fuel vapour inducted at 110 °C in PCCI mode give the best results as the brake thermal efficiency raised from 28.8% for CDC mode to 34.2% for PCCI mode at full load. Additionally, NOX emissions decreased from 615 PPM to 550 PPM, HC emission decreased to 30 PPM, CO emission decreased from 0.09% to 0.06% and a decrease in smoke opacity from 38% to 19.3%.

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).

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.

Effect of Diesel Injection Strategy and Ammonia Energy Fraction on Ammonia-Diesel Premixed-Charge Compression Ignition Combustion and Emissions

The utilization of ammonia as a fuel is one of the effective measures to achieve decarbonization and carbon neutrality in internal combustion engines (ICEs). However, its slow laminar flame speed and high ignition energy limit the efficient application of ammonia-only in ICEs. In this study, based on a heavy-duty single-cylinder engine, the impact of ammonia energy fraction (AEF), start of diesel injection (SODI) timing, and diesel injection pressure (DIP) on combustion and emission characteristics of premixed-charge compression ignition mode under low load conditions was investigated. Combined with three-dimensional simulation, the mechanism of how AEF and diesel injection strategy regulation affected the in-cylinder equivalence ratio and reactivity distribution was analyzed. It was found that increasing the AEF and advancing the SODI timing can improve the homogeneity of mixture. However, the spatial distribution of the OH groups deteriorate continuously. Experimental results indicated that with the used of 50% AEF, 60 MPa DIP, and injecting diesel at −40°CA ATDC, a gross indicated thermal efficiency (ITEg) of 49.7% can be achieved. Compared to the diesel-only mode, the greenhouse gas (GHG) emissions reduced by 44%. To further improve the combustion of ammonia/diesel PCCI mode, the DIP was increased to 100 MPa, which optimized the in-cylinder fuel–air mixing process, improving the homogeneity of the mixture and enhancing the reactivity distribution before the ignition, and enabling faster combustion. As a result, an increase in ITEg to 51.4% with using 100 MPa DIP was achieved, and reduced the GHG emissions by 51% compared to the diesel-only mode.

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.

Numerical investigation on selecting appropriate piston bowl geometry and compression ratio for gasoline-fuelled homogeneous charge compression ignited light-duty diesel engine

The gasoline-fuelled homogeneous charge compression ignition (HCCI) combustion is a promising approach to mitigate the significant limitations of the traditional compression-ignition combustion for light-duty engine applications. In the present work, the required autoignition quality of gasoline was achieved by blending 2-ethylhexyl nitrate (EHN) with gasoline to ensure combustion stability at the achieved engine loads. A reduced chemical reaction mechanism consisting of 185 species and 219 reactions was developed in the present study for EHN-gasoline-fuelled-HCCI combustion. The mechanism was validated by conducting multi-dimensional computational fluid dynamics (CFD) simulations of HCCI combustion in a modified light-duty diesel engine. A detailed numerical study was done using the validated CFD model to select the suitable piston bowl geometry and geometric compression ratio for better engine performance and lower regulated emissions. Eleven different piston bowl geometries were explored, which also included piston bowl designs popular in traditional compression-ignition (toroid) and spark-ignition (flat) engines. The results indicated that the flat-shaped piston bowl exhibited a 17% improvement in the gross indicated thermal efficiency and a 16% and 40% reduction in UHC and CO emissions while maintaining very low NOx and smoke levels compared to the baseline hemisphere-shaped piston bowl. The engine performance remained the same for the flat-shaped piston bowl geometry even for a 17% increased compression ratio with the added benefit that the reduced EHN concentration (by 48 vol.%) was needed to achieve the same combustion phasing. Thus, the present numerical work proposes a promising approach to improve the overall performance of gasoline-fuelled HCCI combustion by piston bowl design and compression ratio optimization.