Indicated Mean Effective Pressure Research Articles

Effect of excess air ratio and ignition timing on the combustion and emission characteristics of the ammonia-hydrogen Wankel rotary engine

As a hydrogen carrier, ammonia can suppress knock and enhance thermal efficiency of the hydrogen-fueled Wankel rotary engine (WRE), and achieve zero carbon emissions. This research established a three-dimensional fluid dynamics model coupled with detailed reaction kinetics of ammonia and hydrogen and verified it based on experiments. Incorporating 10% volume fraction of ammonia into the hydrogen-fueled WRE eliminates knock and decreases the excess air ratio (λ) from 1.8 to 1.4, effectively improving the indicated mean effective pressure (IMEP). The results indicate that when λ exceeds 1.4, flame propagation accelerates with higher concentration of the mixture. This enhances peak in-cylinder pressure and heat release rate, but it results higher NOx emissions. As λ varies from 1.8 to 1.4, NOx emission levels rise by 47.4%. At λ ≤ 1.2, the rapid flame propagation leads to short combustion duration, diminishing the power output. At this stage, the NO formation is dominated by H radicals, and the NOx production reaches its minimum value at λ of 1.0. In summary, the ammonia-hydrogen WRE achieves optimal performance at λ of 1.4 and ignition timing of -5 °CA after top dead center, the indicated thermal efficiency reaches 36.9% and the IMEP achieves 0.683 MPa.

Combustion Analysis of Active Pre-Chamber Design for Ultra-Lean Engine Operation

<div>In this article, the effects of mixture dilution using EGR or excessive air on adiabatic flame temperature, laminar flame speed, and minimum ignition energy are studied to illustrate the fundamental benefits of lean combustion. An ignition system developing a new active pre-chamber (APC) design was assessed, aimed at improving the indicated thermal efficiency (ITE) of a 1.5 L four-cylinder gasoline direct injection (GDI) engine. The engine combustion process was simulated with the SAGE detailed chemistry model within the CONVERGE CFD tool, assuming the primary reference fuel (PRF) to be a volumetric mixture of 93% iso-octane and 7% n-heptane. The effects of design parameters, such as APC volume, nozzle diameter, and nozzle orientations, on ITE were studied. It was found that the ignition jet velocity from the pre-chamber to the main chamber had a significant impact on the boundary heat losses and combustion phasing. The simulation showed that, under 16.46 compression ratio (CR) and 8.93 bar indicated mean effective pressure (IMEP) condition, it is possible to achieve the peak ITE of 49.85% with λ = 2.23.</div>

Investigation of the effect of injection rate shaping on combustion and emissions in heavy-duty diesel engine under steady and transient conditions

The fuel injection rate (ROI) is a crucial factor that affects the combustion and emissions of diesel engines. This study focuses on the injection pressure in a common rail system, which is divided into a high-pressure section and a low-pressure section. A control-oriented ROI shaping (ROIs) model is developed based on the switching strategy between high and low injection pressure. Three types of ROI were generated, namely ROIB (conventional ROI), boot-ROI (low followed by high injection pressure), and anti-boot-ROI (high followed by low injection pressure) respectively. The 1-D and 3-D numerical simulations are conducted to analyze the impact of the shaped ROI on combustion and emissions for steady condition and transient condition. In terms of overall results, boot-ROI shows significant advantage among the three types of ROI. For the steady condition, the boot-ROI was able to increase the IMEP (indicated mean effective pressure) (1.57 bar) at high load conditions with almost unchanged NOx emission. For low load conditions with delayed SOI (start of injection), the exhaust temperature is close to that of the ROIB with a reduction of 0.51 g/kW·h in NOx emissions. For transient condition, the boot-ROI also shows its advantage. It was found to improve the BSFC (brake specific fuel consumption) with almost unchanged NOx emission during load-down process. And in load-up process, the BSFC and soot emission also could be improved with slightly increase in NOx emission through advance of SOI when boot-ROI was adopted. The one-dimensional model using boot-ROI reduces fuel consumption by 2 g/kW·h in experiment with WHTC cycles, with slightly higher soot emission and similar NOx emission.

Low Temperature Combustion Modeling and Predictive Control of Marine Engines

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

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.

Investigation of injection parameters coupled with fuel reactivity on combustion and emissions in dual direct-injection GCI engine

Fuel injection parameters and fuel reactivity significantly affect engine performance, combustion, and emissions. The dual direct-injection strategy could compensate for the insufficient heat release rate to improve the gasoline compression ignition (GCI) mode with medium injection pressure for high loads. This research aims to couple injection parameters and fuel reactivity to optimize the combustion, emissions, and engine performance of the dual direct-injection GCI mode at high loads. The effect of research octane number (RON) of gasoline, injection timing, and injection pressure of dual injection system on combustion and emissions was investigated. Results show that the optimized dual direct-injection GCI mode can simultaneously achieve high thermal efficiency, low emissions, and low maximum pressure rise rate (MPRR) at high loads with the maximum indicated mean effective pressure (IMEP) of about 16 bar with indicated thermal efficiency (ITE) of 48.5%. Delaying the injection timing of injector-1 reduced the peak pressure (Ppeak), MPRR, and NOx emissions. Ppeak, CO, NOx, and indicated specific fuel consumption (ISFC) decreased compared to the dual-injector simultaneous injection case when the injection timing of injector-2 was retarded to between 5 and 10°CA ATDC. Increasing the injection pressure of injector-2 reduced CO, THC, ISFC, and particulate emissions. Lower RON gasoline obtains higher ITE while higher RON gasoline obtains lower particulate emissions.

Numerical investigation on gaseous fuel injection strategies on combustion characteristics and NO emission performance in a pure hydrogen engine

With the proposal of “dual-carbon” goals and increasingly stringent emission regulations, hydrogen as a zero-carbon alternative fuel has great potential in engine applications. In the appliance of pure hydrogen engines, direct injection plus lean burn technology can effectively improve engine performance and reduce emissions. Therefore, this work establishes a three-dimensional (3D) simulation model of the pure hydrogen spark-ignition internal combustion engine (ICE) coupled with chemical reaction kinetics. Then, the applicability of different commonly used hydrogen simplified mechanisms to characterize the combustion process based on experimental data is evaluated, and the feasibility of the transient calculation model is verified. Then, the engine combustion and emission performance are compared by adopting hydrogen port injection (HPI) and hydrogen direct injection (HDI) strategies. Meanwhile, the effects of hydrogen injection timing (HIT) on flow, combustion and nitric oxide (NO) emission processes under direct injection plus lean burn mode are analyzed. The results show that: 1. For mixture distribution at ignition timing (IT), the hydrogen should be distributed near the spark plug and avoid its concentration being too rich since the richer mixture will lead to intense combustion and rapid heat release. 2. When using HDI mode, the engine combustion performance and power performance are better than that of the HPI mode. Delaying HIT, the power performance improves under HDI modes, while both the indicated thermal efficiency (ITE) and indicated mean effective pressure (IMEP) reached the maximum at Case6-HDI-100 with the values are 40.52 % and 0.498 MPa, respectively. 3. Considering the engine combustion, power and emission performance, Case6-HDI-100 (HIT at 100 °CA BTDC) is the preferred scheme. Its ITE and IMEP are 8.49 % and 37.33 % higher than that of Case1-HPI (HPI mode scheme) and 6.50 % and 14.95 % higher than that of Case4-HDI-220 (the lowest scheme under HDI mode), respectively, while nitrogen oxide (NOx) emissions meet the European Stage V non-road emission standards. This study provides some reference values for the combustion design of pure hydrogen ICEs.

Machine learning approaches for identification of heat release shapes in a low temperature combustion engine for control applications

This paper presents the application of machine learning classification algorithms to identify and classify different heat release rate (HRR) shapes to control the combustion for an optimal multi-mode low-temperature combustion (LTC) engine operation. Low-temperature combustion engine produces low nitrogen oxides (NOx) and soot emissions and offers high thermal efficiency. But high in-cylinder pressure rise rates limit the operating range of the LTC engine. Therefore, it is imperative to control combustion in the LTC engine for safe operation. To this end, the HRR traces for over six hundred engine operating conditions are classified using supervised (i.e., Decision Tree, K-Nearest Neighbors (KNN), and Support Vector Machines (SVM)) and unsupervised (i.e., Kmeans clustering) machine learning approaches to segregate different combustion regimes based on HRR shape. Kmeans clustering was not successful in classifying the HRR shapes. Among different supervised machine learning techniques, SVM has proved to be the best method, having an overall classifier prediction accuracy of 92.4% for identifying the distinct shapes using normalized HRR data. In addition, three classifiers have been trained based on the combustion parameters and control inputs. These classifiers are then used as scheduling variables to develop predictive models. A model predictive control (MPC) framework is developed to control multi-mode LTC engine on cycle-to-cycle basis. The MPC framework achieved the simultaneous reference tracking of combustion phasing (CA50) and indicated mean effective pressure (IMEP) while constraining maximum pressure rise rate (MPRR) below 8 bar/CAD.

Construction and verification of dual-fuel engine combustion model

In order to achieve real-time mapping and online optimization of the combustion process of a dual-fuel engine that is in prolonged operation, this paper is the first to combine the Wiebe function with a deep learning neural network to propose a zero-dimensional (0-D) combustion prediction model for a biodiesel-diesel dual-fuel engine. First, the parameters of the double Wiebe functions are calculated by the Pelican Optimization Algorithm (POA), and the operating parameters and Wiebe parameters are used as input and output parameters of neural networks, respectively, to construct parameter identification models. Then, the combustion process is simplified and reconstructed by combining the Wiebe function with the deep learning neural network, and a 0-D prediction model based on the hybrid model-driven and data-driven method is established, which can further obtain combustion results such as cylinder pressure curve and indicated mean effective pressure (IMEP). The results show that the coefficient of determination (R2) value of the dual-fuel engine 0-D prediction model based on the double Wiebe function combined with POA–CNN–Bi-LSTM is 0.9827, and the model has good prediction accuracy and generalization. The development of the combustion model provides reliable numerical model support for the online evaluation and optimization of dual-fuel engine performance.

Assessing the cyclic variability of combustion and NO emissions in hydrogen-methane fueled HSSI engine via quasi-dimensional modeling under the influence of flame-kernel turbulence and equivalence ratio variation mechanisms

This paper assesses the cyclic variability (cycle-by-cycle variations (CCV)) of combustion, performance and nitric oxide (NO) emissions in high-speed (HS), spark-ignition (SI) engine fueled with hydrogen-enriched methane (CH4), for which experimental data are available. Thus, in-house, two-zone, quasi-dimensional turbulent combustion model is used that closely trails the flame-front movement, which was validated before regarding performance, emissions, exergy, and CCV for gasoline- or methane-run HSSI engines. It is enhanced herein to study CCV of performance, combustion, and NO emissions, with engine fueled by various hydrogen-methane blends (up to 50 % by vol. hydrogen) and equivalence ratios (EQR). Hence, the influence of flame-kernel turbulence and EQR variation mechanisms on CCV attributes is considered and assessed. The numerical results are compared with measured data of cylinder pressure, indicated mean effective pressure (IMEP), and NO emissions at ‘steady’ conditions, and further for validation against available experimental CCV results for IMEP at all operating conditions. That CCV analysis is extended to peak pressure, IMEP, and NO emissions using coefficients of variation (COV), frequency distributions, and pertinent diagrams illuminating their cycle-by-cycle variations. The CCV variations decrease with hydrogen content in the blend whereas they increase with the mixture leanness delineating the relative merits of the two mechanisms.

Comparative evaluation of different operating parameters on performance, combustion, and emission characteristics in gasoline compression ignition (GCI) engine by using carbon neutrally biofuels

The stringent emission regulations and energy shortage put forward strict requirements for highly efficient and clean combustion for internal combustion engines. The gasoline compression ignition (GCI), which is a new advanced combustion concept, can obtain high efficiency and low emissions simultaneously without many modifications of standard diesel engines. However, little research has been carried out to synergistically optimize the operation parameters in a wide load range, especially fueled with the carbon neutrally biofuels. Therefore, in this paper, the effects of various operating parameters on engine performance, combustion, and emission characteristics of the gasoline compression ignition (GCI) strategy fueled with a blend of butanol and biodiesel were investigated. Specifically, the impact of butanol energy ratio, fuel direct injection timing, and exhaust gas recirculation (EGR) at the indicated mean effective pressure (IMEP) of 4, 8, and 14 bar and the butanol energy ratio of 60%, 70%, and 80% were examined. Result shown that the increase in butanol energy ratio decreased the fuel reactivity and worsen the combustion process, while the lower butanol energy was also disadvantage to the engine performance. The indicated thermal efficiency could achieve 48.5% when the butanol energy ratio was 70% at medium engine load. The earlier fuel injection timing was needed at low engine load, the EGR was necessary to inhibit the in-cylinder pressure rise at high engine load, in which the EGR rates of 20% at the IMEP of 8 bar and 30% at the IMEP of 14 bar could achieve the optimum engine performance, respectively. Meanwhile, the nitrogen oxides emissions shown a greatly decrease with the EGR rates increase, and it was less than 200 ppm at the IMEP of 14 bar when the EGR rates were 50%.

Combustion cycle-to-cycle variations of opposed-piston two-stroke gasoline direct injection engine

The combustion characteristics and cycle-to-cycle variations of opposed-piston two-stroke (OP2S) gasoline direct injection (GDI) engine are investigated with experiment. The effects of engine speed on the combustion process and cycle-to-cycle variations are discussed. This paper chooses the indicated mean effective pressure, the maximum cylinder pressure and the maximum pressure rising rate to characterize the combustion cycle-to-cycle variations. The heat release rate of OP2S-GDI engine is in accordance with the conventional gasoline engine, which is divided into flame developing period, rapid burning period and after burning period. With the increase of engine speed, the maximum combustion pressure and maximum pressure rise rate decrease, and the time corresponding to the maximum in-cylinder pressure is delayed. The pressure rise rate associated with different engine speeds all show an increasing trend, with maximum values less than 0.2 MPa/°CA. The peak value of instantaneous heat release rate in the combustion process decreases and the combustion amount in the post-combustion period increases as the engine speed increases. The cycle-to-cycle variation rate of indicated mean effective pressure (IMEP) increases as the engine speed increases. The maximum IMEP cycle-to-cycle variation rate is 6.101% at 4000 rpm, which is less than the traditional gasoline engine cycle-to-cycle variation rate (10%). The cycle-to-cycle variation rate of the maximum cylinder pressure ( pmax) increases as the engine speed increases. The pmax cycle-to-cycle variation rate is 1.083% at 4000 rpm, which is less than traditional gasoline engine cycle-to-cycle variation rate (2%). The R ( pmax, pi) is weakly correlated at 2000 rpm and uncorrelated at 3000 rpm and 4000 rpm. The R( θ( pmax), pi) is strongly correlated at 3000 rpm and uncorrelated at 2000 rpm and 4000 rpm. The cycle-to-cycle variation rate of the maximum pressure rise rate (d p/d φ) is 7.406%%, 7.919% and 7.667% respectively at 2000 rpm, 3000 rpm and 4000 rpm. The R ((d p/d φ) max, pi) is weakly correlated at different engine speed, the R( θ(d p/d φ) max, pi) is moderately correlated at 2000 rpm and positive correlation at 3000 rpm and 4000 rpm.

Effects of hydrogen blending ratio on combustion and emission characteristics of an ammonia/hydrogen compound injection engine under different excess air coefficients

Currently, hydrogen and ammonia are the best green, zero-carbon energies worldwide. Applying ammonia and hydrogen to internal combustion engines is a top priority for achieving the dual-carbon goal for the automotive industry. However, both ammonia and hydrogen have disadvantages that make them unsuitable for use as fuels on their own. Hydrogen internal combustion engines can suffer from abnormal burning, such as premature ignition, backfiring, and detonation. At the same time, the difficulty of hydrogen storage, transportation, and refilling can also lead to the problem of high cost of use. Ammonia suffers from high ignition energy, poor flame-spreading speed, and inadequate burning stabilization. When used alone, it causes incomplete combustion of large amounts of ammonia. Therefore, our group uses the spray pattern of “hydrogen direct injection (HDI) plus ammonia port injection (API). ” The influence of hydrogen blending ratio (HBR) on the combustion and emission characteristics of an ammonia/hydrogen compound injection engine with various excess air coefficients (λ) is investigated. The blending ratios of hydrogen are 6.1 %, 16.8 %, 27.3 %, 37.7 %, 47.8 %, and 57.7 %, respectively. The experimental data suggests that the indicated mean effective pressure (IMEP) shows an incremental trend as the hydrogen blending ratio grows. Not only CA0-10 but also CA10-90 have been reduced. The whole combustion process is shortened. The temperature and pressure rise. When the ratio of hydrogen blending is higher than 27.3 %, the enhancement of the burning characteristics by hydrogen is not apparent. NOX emissions rise with the ratio of hydrogen blending. NH3 emissions tend to drop as the blending ratio of hydrogen rises. Combining the emission and combustion characteristics, the general engine performance is better when the λ is 1.2 and the ratio of hydrogen blending is 27.3 %.

Real-time predictive model for reactivity controlled compression ignition marine engines

Model-based design is proven to be essential for the development of control systems. This paper presents a real-time predictive control-orientated model (COM) for low-temperature combustion (LTC), dual-fuel, reactivity-controlled compression ignition (RCCI) engines. A comprehensive model-based design methodology must be capable of constructing an RCCI control-orientated model with high accuracy, high noise immunity, good response, predictivity in governing mechanisms, and low computation time. This work attains all of these for the first time for a cutting-edge RCCI marine engine. The real-time model (RTM) captures the key sensitivities of RCCI by controlling the total fuel energy and the blend ratio (BR) of two fuels, while also considering uncertainties arising from variations of inlet temperature and the gas exchange process. It provides not only the cycle-wise combustion indicators but also the crank-angle-based cylinder pressure trend. The RTM is derived by direct linearisation of a physics-based model and is successfully validated against experimental results from a large-bore, RCCI engine and the previously acknowledged UVATZ (University of Vaasa Advanced Thermo-kinetic Multi-zone) model. Validation covers both steady-state and transient modes. With high accuracy in several case studies representing typical load transients and air-path disturbance rejection tests, the model predicts maximum cylinder pressure (Pmax), crank-angle of 5 % burnt (CA5), crank-angle of 50 % burnt (CA50) and indicated mean effective pressure (IMEP) with root means square (RMS) errors of 8.6 %, 0.3 %, 0.6 %, and 0.6 % respectively. The average simulation time without any code optimisation is around 5 ms/cycle, offering sufficient real-time surplus to incorporate a semi-predictive emission submodel within the current approach.

Flame Characteristics and Abnormal Combustion of Methane Port Injection and Isooctane Direct Injection with Injection Timings Considered

Natural gas (NG) is a low-carbon fuel that can achieve low carbon emissions and high efficiencies. However, the low mean molecular mass and low energy density of methane result in low engine performance, and blending methane with gasoline is an effective way of improving the performance of NG engines. In this study, flame characteristics (including abnormal combustion) and engine performance are optically studied under methane port injection and isooctane direct injection conditions. The results indicate that the addition of isooctane can significantly increase the power output of NG engines. Under partial-load conditions, the minimum ignition advance for best IMEP is delayed with the addition of isooctane because of the higher flame speed of isooctane, and isooctane addition primarily improves the turbulent flame propagation rather than the initial flame formation. As for the isooctane injection timing, the indicated mean effective pressure (IMEP) first increases and then decreases with the delay in isooctane injection. The hot spots in the flame images confirm that late injection results in isooctane inhomogeneity, which reduces the engine’s thermal efficiency. At high loads, the low energy density of methane can lower the knocking intensity, even in the presence of auto-ignition at a speed of 120.7 m/s. The knocking pressure can lead to the ejection of oil droplets, which can increase the flame speed in the subsequent cycle.

Combustion characteristics and performance of a Wankel engine for unmanned aerial vehicles at various altitudes

This study investigates the effects of altitude on the combustion, emissions, and performance of a Wankel engine for unmanned aerial vehicles (UAVs). The main motivation behind the presented study is to contribute to the Wankel engine designs used as a power source in UAVs by revealing the operating conditions at various altitudes. For these purposes, a gasoline fueled Wankel engine was simulated at sea level conditions for different equivalence ratios and results were validated with their experimental counterparts. Then, CFD simulations were carried out at various altitudes (6000 ft, 10,000 ft, and 15,000 ft). The simulation results show that decreasing ambient air temperature, and pressure at higher altitudes reduces the fresh charge density, hence combustion efficiency and heat release rate (HRR). As a result, the performance characteristics such as the indicated mean effective pressure (IMEP), the indicated torque, and indicated power decrease and exhaust emissions increase. For 6000 rpm, IMEP decreases by 39.11%, 53.79%, and 69.22%, and the indicated power reduces by 35.51%, 52.47%, and 65.05% at the altitudes of 6000 ft, 10,000 ft, and 15,000 ft, respectively, compared to those obtained at the sea level conditions. As for exhaust emissions, CO and CO2 are lowest at sea level conditions and increase with altitude.

Analysis of the fractal characteristics for combustion instability in a premixed natural gas engine

To investigate the influence of gas injection timing (GIT) on the combustion instability of a premixed natural gas engine, experiments were conducted under low load conditions using various GITs. Multifractal and multiscale entropy analyses were employed to examine the fractal characteristics and complexity of the experimental time series for indicated mean effective pressure (IMEP) and heat release (Q) at different scales. Statistical analysis and return maps of the IMEP and Q time series were utilized to verify the results. The findings revealed that the combustion process of the natural gas engine demonstrates clear fractal characteristics at different scales. A strong correlation is found between the combustion instability and the fractal characteristics. Furthermore, the probability densities of the IMEP and Q time series exhibit super-Gaussian distributions. Retarding the GIT results in an initial increase, followed by a decrease in the difference value of the Hurst index and singular spectrum width. The mapping point distributions of the IMEP and Q time series initially disperse and subsequently concentrate. The fractal complexity and chaotic characteristics of combustion instability initially strengthen and then gradually diminish. Moreover, under lower load conditions, the anti-persistent correlation becomes more pronounced, and the intermittence and complexity of the fractal characteristics also intensify, signifying a more significant impact of GIT on the combustion instability of the natural gas engine. Notably, when the GIT is approximately 60°CA after top dead center, the combustion process exhibits stronger fractal characteristics, accompanied by a greater dispersion degree of the mapping points. This study provides a theoretical basis for enhancing the lean-burn stability of natural gas engines.

Effects of ammonia addition on knock suppression and performance optimization of kerosene engine with a passive pre-chamber

The spark-ignition (SI) engine fueled kerosene faces the significant risk of knocking. Ammonia can be considered as a knock inhibitor to suppress the knock and optimize the performance of the kerosene engine, which also has excellent potential for reducing carbon emissions from internal combustion engines (ICE). In this paper, the effects of ammonia addition on the combustion characteristics, knock intensity, and performance of the kerosene engine with pre-chamber turbulent jet ignition (PTJI) were investigated experimentally. The results show that the knock intensity of the PTJI kerosene engine is reduced after adding ammonia and the knock tolerance is significantly broadened. The PTJI kerosene engine achieves full load operation at the compression ratio (CR) of 9 without knocking occurrence after blending ammonia, and the maximum increase of the indicated mean effective pressure (IMEP) and thermal efficiency is 2.95 bar and 12.6%, respectively. An advanced spark timing (ST) is obtained under ammonia addition conditions, resulting in higher in-cylinder pressure and superior combustion performance. The ignition delay ST-CA10 and combustion duration CA10-CA90 are prolonged as the ammonia ratio (ENH3) increases. An optimization operating strategy for the kerosene engine was proposed based on the CR, engine speed, supercharging, and ammonia addition. The best thermal efficiency of 26.88% with an IMEP of 8.25 bar is obtained at 1500 rpm, CR = 9, ENH3 = 20%, and a further improvement of engine power (IMEP > 12.0 bar) is achieved by supercharging.

Custom-Designed Pre-Chamber: Investigating the Effects on Small SI Engine in Active and Passive Modes

This work shows the results of an experimental campaign carried out in two spark ignition engines, a small optical research engine and its commercial counterpart, using a turbulent ignition system (pre-chamber) specifically designed for small engines. Advanced optical techniques and conventional methods were used to study the combustion process under various operating conditions. The pre-chamber operated actively in the research engine and passively in the commercial engine. Results showed that the pre-chamber configuration resulted in an increase in indicated mean effective pressure (IMEP) and a decrease in the coefficient of variation (CoV) of IMEP. These improvements compensated for challenges such as slow methane combustion rate, poor lean burn capability, and air displacement. In addition, the pre-chamber configuration exhibited lower fuel consumption and specific exhaust emissions compared to the standard ignition system. The novelty of this work lies in the successful implementation of the turbulent ignition system as a retrofit solution for SI engines, showing improved combustion efficiency and lower emissions. The study goes beyond previous efforts by demonstrating the benefits of the pre-chamber configuration in small engines without requiring extensive modifications. The results provide valuable insights into the automotive industry’s pursuit of engine optimization and highlight the significance of innovative approaches for spark ignition engines in contributing to sustainable mobility.

Potential of the reverse-reactivity controlled compression ignition (R-RCCI) combustion for maintaining ultra-low emissions and enhanced thermal efficiency

Focusing on the reverse-reactivity controlled compression ignition (R-RCCI) concept, the intake and fuel supply parameters were optimized using a promoted genetic algorithm combined with the computational fluid dynamics simulation in this investigation. The combustion characteristics and energy utilization of both gasoline partially premixed combustion (PPC) and polyoxymethylene dimethyl ethers (PODEn)/gasoline R-RCCI were further evaluated in detail. The results indicated that R-RCCI exhibits superior performance compared with PPC. The optimized gross indicated thermal efficiency (ITE) of R-RCCI is 3.9% and 2.6% higher than that of PPC under 4 and 7 bar indicated mean effective pressures (IMEPs), respectively. The premixed high-reactivity PODEn in R-RCCI decreases the needed intake temperature, which provides more flexibility for the combustion phasing control. This correspondingly results in improved thermal efficiency for R-RCCI at 4 bar IMEP. Meanwhile, the lower intake temperature helps to decrease the heat transfer loss under 7 bar IMEP. Moreover, R-RCCI exhibits significant superiority over PPC on the unburned hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (NOx), and soot emissions under the operating conditions investigated in this work. For R-RCCI, the pre-combustion of PODEn can create a thermal atmosphere containing accumulated oxygen radicals, which provides the reaction conditions for the subsequent gasoline oxidation.