International Journal of Engine Research

Spark ignition–controlled auto-ignition is a combustion strategy to overcome the challenges in a homogeneous charge compression ignition or controlled auto-ignition combustion which has a limited operation region and does not have any direct control of the combustion timing. However, the spark ignition–controlled auto-ignition combustion can result in a large cyclic variability due to two main distinctive combustion phases developing initially by flame propagation and following controlled auto-ignition combustion throughout an engine cycle. Characterization of combustion development is, therefore, required to maintain a stable engine operation under spark ignition–controlled auto-ignition combustion. In this research, experimental studies were carried out to investigate spark ignition–controlled auto-ignition combustion development at different spark advances and intake air temperatures. Combustion analyses were performed employing pressure-based heat release and mass fraction burn curve to determine the main combustion parameters along with transition points (corresponding to crank angles) to controlled auto-ignition and mass fraction burnt by flame propagation. The results reveal that transition point has a strong correlation with crank angle position where 10% of fuel mass consumed combustion phasing rather than mass fraction burnt by flame propagation at the same intake air temperature. The cycles with a higher mass fraction burnt by flame propagation can result from early flame development at the advanced spark timings (at −30 and −40 °CA) while the slow flame development at a spark timing of −20 °CA due to late transition point corresponding to crank angle occurred. Besides, it is also found that flame propagation phase more contributes to the cyclic variation in the whole combustion process.

The oil and gas industry operates by reciprocating natural gas engines which must comply with regulated emission standards for hazardous air pollutants, including NOx, CO, and volatile organic compounds (VOCs). These pollutants are regulated by Environmental Protection Agency, and each engine is regularly tested for compliance with national emission standards. A general emissions control strategy in combustion engines is to control the air-to-fuel ratio. However, stationary reciprocating engines, especially two-stroke engines, rarely have any mechanisms to control air and fuel parameters at various operating conditions. This article discusses a novel air management system that is invented to control the air-to-fuel ratio for a large bore two-stroke naturally aspirated gas engine, that is, AJAX™ brand model number 2802. The method can also be used for other engines with the same working principle. This novel air management system has been developed through comprehensive computational analyses of the gas exchange process inside the engine and is presented here. Pilot tests have also been conducted to validate the computational model results. The results show that this air management system can significantly reduce the engine emissions to the standard level at various operating conditions, including partial loads and speeds. In the case of VOCs emissions, up to a 75% reduction is observed.

Performance of lean-burn gasoline spark-ignition engines can be enhanced through hydrogen supplementation. Thanks to its physicochemical properties, hydrogen supports the flame propagation and extends the dilution limits with improved combustion stability. These interesting features usually result in decreased emissions and improved efficiencies. This article aims at demonstrating how hydrogen can support the combustion process with a modern combustion system optimized for high dilution resistance and efficiency. To achieve this, chemical kinetics calculations are first performed in order to quantify the impacts of hydrogen addition on the laminar flame speed and on the auto-ignition delay times of air/gasoline mixtures. These data are then implemented in the extended coherent flame model and tabulated kinetics of ignition combustion models in a specifically updated version of the CONVERGE code. Three-dimensional computational fluid dynamics engine calculations are performed at λ = 2 with 3% v/v of hydrogen for two operating points. At low load, numerical investigations show that hydrogen enhances the maximal combustion speed and the flame growth just after the spark which is a critical aspect of combustion with diluted mixtures. The flame front propagation is also more isotropic when supported with hydrogen. At mid load, hydrogen improves the combustion speed and also extends the auto-ignition delay times resulting in a better knocking resistance. A maximal indicated efficiency of 48.5% can thus be reached at λ = 2 thanks to an optimal combustion timing.

This article presents the experimental validation of a complete integrated one-dimensional twin-scroll turbine model able to be used in reciprocating internal combustion engine unsteady simulations. A passenger car with a twin-entry-type turbine has been tested under engine-like pulse conditions by means of a specifically built gas stand. To obtain high-resolution quality data, the turbine and turbine line pipes have been instrumented with mean and instantaneous pressure sensors as well as temperature and mass flow sensors, employing a uniquely designed rotating valve for the pulse generation. This experimental configuration enables to obtain the pressure decomposition in both inlets and outlets of the turbine. Using the experimental data obtained, the model is fully validated, with special focus on the reflected and transmitted components for analysing the performance of the model and its non-linear acoustics prediction capabilities. The model presents a very high degree of correlation with the experimental results, providing a range of errors similar to the uncertainty of the measurements, even in the medium- and high-frequency spectra.

To fulfill the future NOx emission regulations, the use of exhaust gas recirculation could be necessary for the engine starting at cold conditions. In this context, condensation inside the exhaust gas recirculation line could appear, affecting in several ways the engine components and their life span. In this article, a mathematical model is developed with the aim of predicting the conditions that produce the condensation phenomenon to appear inside the exhaust gas recirculation circuits of an internal combustion engine working at low ambient temperatures (−7 °C). In particular, the humidity ratio and the internal engine conditions that characterize the appearance of this phenomenon are estimated by the model. The model is validated by experimentally visualizing the condensation behavior along a representative driving cycle by means of cameras fitted on the exhaust gas recirculation rail. This validation process shows that the predictions made by the model are in good agreement with the results obtained from the experimental tests.

Engines operating in low temperature combustion during positive valve overlap operation offer significant benefits of high fuel economy over the low temperature combustion during negative valve overlap operation. Significant efficiency improvement was achieved by the increased gamma and lower pumping loss. However, NOx emissions were increased due to reliance on the flame-induced combustion. In this study, the corona ignition system was evaluated to reduce NOx emissions during positive valve overlap operation while maintaining the benefit of efficiency gain. The tests were performed in a 2.2-L multi-cylinder engine. The results show that the ignition delay is always shorter with the corona ignition system than with the spark plug. The corona ignition system is able to support stable combustion (coefficient of variation of indicated mean effective pressure <3%) in a lower load during positive valve overlap operation than the spark plug, which gives us additional efficiency benefit. Since the corona ignition system promotes simultaneous ignition of the mixture at multiple locations in the combustion chamber as opposed to ignition being limited to the spark gap channel, the dependence of the flame burn for stable combustion during positive valve overlap operation minimizes, which leads to lower NOx emissions over the spark plug.

Modern diesel engine aftertreatment systems require elevated temperatures for effective reduction of engine-out emissions. Maintaining elevated aftertreatment temperatures in a fuel-efficient manner is a challenge, especially at low-load engine operation where engine-outlet temperatures are low; therefore, higher engine-outlet temperatures are typically achieved via increased fuel consumption. Previous studies have demonstrated that strategies such as cylinder deactivation (method where there is neither valve motion nor fuel injection in a subset of cylinders, thereby isolating the deactivated cylinders from the gas exchange process) and cylinder cutout (method where there is no fuel injection in a subset of cylinders, implemented with high recirculated gas rates) reduce fuel consumption while elevating engine-outlet temperatures, by reducing the overall airflow through the engine. This article introduces and characterizes “non-fired cylinder ventilation” as alternate means to achieve fuel-efficient aftertreatment thermal management, by reduction of overall airflow through the engine. Fuel injection is deactivated from a subset of cylinders during non-fired cylinder ventilation, and the non-firing cylinders participate in the gas exchange process with the same manifold at a time, thereby reducing the intake-to-exhaust manifold gas exchange through the cylinders. It is demonstrated that non-fired cylinder ventilation shows similar fuel efficiency and thermal management as cylinder deactivation when the valves of the non-firing ventilated cylinders are open by at least 4 mm, due to similar, negligible, gas-exchange losses, while non-fired cylinder ventilation with lower valve lifts enables elevated engine-outlet temperatures with relatively higher fuel consumption than cylinder deactivation. Non-fired cylinder ventilation strategies demonstrate 75 °C higher temperatures at fuel-neutral conditions, and up to 35% fuel savings at similar temperatures, compared to six-cylinder operation.

From the different power plants, the compression ignition diesel engines are considered the best alternative to be used in the transport sector due to its high efficiency. However, the current emission standards impose drastic reductions for the main pollutants, that is, NOx and soot, emitted by this type of engines. To accomplish with these restrictions, alternative combustion concepts as the premixed charge compression ignition are being investigated nowadays. The objective of this work is to evaluate the impact of different fuel injection strategies on the combustion performance and engine-out emissions of the premixed charge compression ignition combustion regime. For that, experimental measurements were carried out in a single-cylinder medium-duty compression ignition diesel engine at low-load operation. Different engine parameters as the injection pattern timing, main injection timing and main injection fuel quantity were sweep. The best injection strategy was determined by means of a methodology based on the evaluation of a merit function. The results suggest that the best injection strategy for the low-load premixed charge compression ignition operating condition investigated implies using a high injection pressure and a triple-injection event with a delayed main injection with almost 15% of the total fuel mass injected.

The combustion and emission characteristics of a dual-fuel spark-ignition engine with direct injection of gasoline surrogates and port injection of ethanol were studied. Toluene reference fuel with different research octane number namely TRF#1, TRF#2, TRF#3, TRF#4 and TRF#5 were employed as gasoline surrogates, in which TRF#1 with high octane number was to simulate commercial gasoline under direct-injection spark-ignition mode as comparison. For dual-fuel spark-ignition mode, the ethanol port-injection ratios were 21%, 25%, 29%, 32% and 35%, respectively. The results demonstrated that with the increase of the ethanol ratio, the knock-limited spark timing was advanced gradually. The emissions of hydrocarbon, ethane, propylene, isopentane, cyclohexane and aromatic hydrocarbons reduced while CO, NOx, ethylene, acetaldehyde and ethanol increased. Compared to TRF#1 in direct-injection spark-ignition mode, the indicated thermal efficiencies of dual-fuel spark-ignition mode were slightly lower under most test conditions. When direct injection of TRF#3, TRF#4, TRF#5 and the ethanol ratio was higher than 29%, some of the indicated thermal efficiencies of the engine were consistent with or higher than that of TRF#1 in direct-injection spark-ignition mode. Based on dual-fuel spark-ignition mode and with the assistance of port injection of ethanol, the indicated thermal efficiency of low research octane number fuels was comparable to that of TRF#1 in direct-injection spark-ignition mode.

Polyoxymethylene dimethyl ethers, with excellent volatility and oxygen content of up to 49%, have great potential to improve engine performance and emission characteristics. In this study, experiments were carried out in a single-cylinder engine fueled with gasoline/diesel/polyoxymethylene dimethyl ethers blend fuel using multiple premixed compression ignition combustion mode along with engine optimization to exploit the high-efficiency potential. The thermal efficiency was increased by 9.4 percentage points after transforming the combustion mode from conventional diesel mode to gasoline/diesel/polyoxymethylene dimethyl ethers multiple premixed compression ignition mode. A fully variable valve system and a redesigned low-heat-transfer piston were used to further improve the thermal efficiency. The low-heat-transfer piston had a 15% lower area–volume ratio compared with the original ω-type piston. By replacing the original ω-type piston with the low-heat-transfer piston, the heat transfer loss was reduced by 2.29 percentage points and thus indicated thermal efficiency could be increased by 2.37 percentage points, which was up to 50.03%. On the basis of the low-heat-transfer piston, indicated thermal efficiency could be further increased to 51.09% with the application of fully variable valve system due to the longer ignition delay and more premixed combustion. At the same time, NO_X emissions could be controlled below 0.4 g/kW·h using high exhaust gas recirculation ratio, which equaled the NO_X emission limit of Euro VI standard. Although soot emissions could be increased due to weak turbulence and insufficient intake charge using the low-heat-transfer piston and fully variable valve system, it was still lower than those of the original diesel engines.

It has been reported that early combustion in a spark-ignition engine determines the subsequent combustion. Also, the early combustion has a very strong correlation with cycle-to-cycle variability, which limits engine operating range. As such, accurate modeling of the early flame development is very important in accurate simulation of spark-ignition engine combustion. During the early flame development, the flame kernel, initiated by spark, grows initially at laminar flame speed. As the kernel grows, the flame surface wrinkles due to surface instability and interacts with the flow turbulence as the flame transitions from laminar to turbulent flame. In this study, a semi-empirical model is proposed to simulate the laminar-to-turbulent flame transition process during early spark-ignition combustion. A hyperbolic tangent function was used to emulate the laminar-to-turbulent flame speed transition process. The proposed transition function was evaluated during early flame kernel development for both Reynolds-averaged Navier–Stokes and large eddy simulation models against combustion analysis data from high-speed optical particle image velocimetry. Difference in Reynolds-averaged Navier–Stokes and large eddy simulation transition function was analyzed and discussed.

Due to the market presence that natural gas has and is expected to have in the future energy sector, research and development of novel natural gas combustion strategies to increase power density, lower total emissions, and increase overall efficiency is warranted. Dilution whether by excess air or by exhaust gas recirculation has historically been implemented on diesel, natural gas, and gasoline engines to mitigate various regulated emissions. In the large industrial natural gas engine industry, excess air dilution or ultra-lean-burn operation has afforded lean-burn engines increased power density and reduced NO _x emissions. This advance in technology has allowed lean-burn engines to compete in markets such as electrical power generation which previously they had not been able. However, natural gas engines utilizing a non-selective catalytic reduction system or three-way catalyst must operate under stoichiometric conditions and thus are limited in power density by exhaust gas temperatures. In previous gasoline small engine research, a novel exhaust gas recirculation technique called dedicated exhaust gas recirculation was shown to have a positive impact on engine-out emissions of NO _x and unburned hydrocarbons while also lowering exhaust component temperatures. This work seeks to understand the consequences of implementing a dedicated exhaust gas recirculation system on a multi-cylinder stoichiometric industrial natural gas engine. The results of this initial evaluation demonstrate reductions in engine-out NO _x and CO emissions and improvements in engine-out exhaust gas temperatures with the dedicated exhaust gas recirculation technique. However, in a low-turbulence combustion chamber, dedicated exhaust gas recirculation significantly lowers the overall rate of combustion and results in significant differences in cylinder-to-cylinder combustion.

E-Fuels can play a significant role in decarbonizing the transport sector. Among the potential E-fuels, dimethyl ether is a promising candidate for the combustion in compression ignition engines. Together with methanol, it can be produced from synthesis gas in a combined single-step process. However, due to the low volumetric heating value of dimethyl ether, the fuel injection system has to be modified to realize higher fuel flow rates. In this study, two injectors with increased nozzle hole diameters have been investigated, and their impact on engine performance, particle number distribution and formaldehyde as well as methane emissions was assessed. It was found that with dimethyl ether as fuel, the indicated efficiency at high load could be increased by over 1% compared to operation with conventional diesel fuel. The main reason for this is lower wall heat loss. Furthermore, almost no particle emission was found during dimethyl ether operation with the smaller nozzle. With the larger nozzle hole diameter, increased particle concentrations were measured at high loads. But these were still much lower compared to the corresponding diesel fuel combustion. Regarding formaldehyde and methane, higher emissions were found for the dimethyl ether combustion compared to diesel fuel combustion. It is assumed that this is due to the increased formaldehyde and methane production of dimethyl ether during high temperature pyrolysis and oxidation. The increased hydrocarbon emissions could have been caused by fuel dripping from the nozzle after the end of the injection event.

A urea injection control strategy for urea-selective catalytic reduction under a transient process is investigated on a heavy-duty diesel engine test bench in this study. The aim is to improve NO _x conversion efficiency and reduce ammonia slip. With the selective catalytic reduction system as the research object, an open thermodynamic conservation system is established. The conservation relationship in the process of urea injection, NO _x reduction reaction, ammonia storage, and ammonia slip is investigated. The ideal target ammonia storage area and the ammonia storage characteristics during the transient process are studied. The ammonia storage area and boundary, which change with the transient temperature, are established. Correction of real-time ammonia injection is further deduced from the boundary of the area. The world harmonized transient cycle test cycle result showed that compared to feed-forward control, the NO _x conversion efficiency increased by 16% and the NH₃ slip decreased by 75% when using the proposed real-time ammonia storage-management control method.

In this study, a new form of hybrid pneumatic combustion engine based on compressed air injection boosting is proposed. The hybrid pneumatic combustion engine regenerates the wasted energy during engine brake to improve the engine performance achieving better fuel economy. The mathematic model of the hybrid pneumatic combustion engine including a supercharged engine and the compressed air tank has been established. The steady-state and transient performance of the engine are analysed. Results show that the air injection boosting system can effectively improve the steady-state performance. Under the speed of 1900 r/min and 100% load, the engine torque and power can be increased from 1039 N m, 206.9 kW to 1057 N m, 210 kW by adopting air injection boosting with the injection pressure of 0.5 MPa. Effects of air injection parameters are also studied, showing that better performance can be achieved under higher air tank pressure and larger injection hole diameter. In addition, a transient analysis is completed under the speed of 1100 r/min. The result shows that when air injection boosting is used, the responding time of the engine to an instant load increase can be potentially reduced from 5.5 to 3.5 s under the injection pressure and duration of 0.5 MPa and 3 s. Meanwhile, the tank pressure has limited influence on the transient performance of the engine.

In this experimental study, a production grade engine was modified to operate in two combustion modes, namely conventional diesel combustion (CDC) and premixed charge compression ignition (PCCI) combustion, depending on the engine load. For mode switching, an open electronic control unit was programmed to operate the engine in PCCI combustion mode up to medium engine loads and then automatically switching it to CDC mode at higher engine loads, by varying the fuel injection parameters and the exhaust gas recirculation rate. For performance and emission characterization in the entire load range (idling-to-full load) of the test engine, a test cycle of 300 s was used, which included CDC mode, PCCI combustion mode, and transition between these two modes. Results showed that both mineral diesel and B20 (20% biodiesel blended with mineral diesel, v/v) fueled PCCI combustion resulted in significantly lower NO_x and particulate emissions compared to baseline CDC. Relatively lower exhaust gas temperature in PCCI combustion mode led to slightly inferior engine performance and higher concentration of unregulated emission species such as SO₂, HCHO, and so on. B20-fueled engine resulted in relatively lower unregulated emission species and particulates compared to the mineral diesel–fueled engine in both the combustion modes. In CDC mode, contributions of accumulation mode particles were significantly higher compared to nucleation mode particles. Relatively lower emission of aromatic compounds in PCCI combustion mode compared to CDC mode was another important finding of this study; however, B20-fueled engines resulted in slightly higher emissions of aromatic compounds.

A mathematical correlation is developed, based on the thermodynamic model of a downsized gasoline engine, to establish the numerical relationship among the thermodynamic parameters of the combustion chamber. In the developed numerical model, the in-cylinder pressure curves of various operation conditions are simulated by varying the air–fuel ratio in the cylinder, and the associated knock characteristics are recorded. The accuracy of the numerical simulation results is verified against the knock excitation experiment. Then, based on the Rover K16 gasoline engine, a simulation model is developed to simulate the engine knock in the combustion chamber and observe the force acting on the top surface of the piston. The results show that the forces, which act on the piston top surface, are varying at various locations at the same time, and the largest forces occur at the edge of the piston and followed by the piston centre. Then, by comparing the thermo-mechanical coupling strength of the piston under different operating conditions, the results show that the occurrence of the knocking does not exceed the piston’s strength limit. However, the stress and deformation value of the piston is increased significantly, and the failure point of the piston position is changed. Finally, based on the calibrated strength results, the piston durability is predicted for various engine knock conditions. The results show that there is an initial damage of piston in the process of detonation at the surface of the piston pin hole and the joint of the piston cavity. The gasoline engine finally has a predicted mileage of 2,53,440 km continuously, which meet the prescribed mileage of 2,20,000 km.

In the last few years, increasing concern about the harmful effects of the use of fossil fuels in internal combustion engines has been observed. In addition, the limited availability of crude oil has driven the interest in alternative fuels, especially biofuels. In the context of spark ignition engines, bioalcohols are of great interest owing to their similarities and blend capacities with gasoline. Methanol and ethanol have been widely used, mainly due to their knocking resistance. Another alcohol of great interest is butanol, thanks to its potential of being produced as biofuel and its heat value closer to gasoline. In this study, a comparative study of gasoline–alcohol blend combustion, with up to 20% volume, with neat gasoline has been carried out. A single-cylinder, variable compression ratio, Cooperative Fuel Research-type spark ignition engine has been employed. The comparison is made in terms of fuel conversion efficiency and flame development angle. Relevant information related to the impact in the combustion process of the use of the three main alcohols used in blends with gasoline has been obtained.

Consideration of internal combustion engine formats suitable for hybrid or range extender electric vehicles usually focuses on selecting a power plant, which is as compact as possible to meet the demands and constraints of the installation. In-line three-cylinder engines often provide an attractive solution for such vehicles. This article presents a low emission two-stroke engine of in-line three-cylinder format and draws a comparison with an equivalent four-stroke engine. The particular focus of the analysis is on strategies for minimization of noise, vibration and harshness with significant reduction in piston lateral force compared with the four-stroke unit. The design also considers a balance shaft arrangement to further assist with noise, vibration and harshness reduction. The presented arrangement demonstrates an integrated induction control/balance shaft arrangement, which erodes the usual cost penalties typical of balance shaft consideration in three-cylinder engines.

In modern gasoline direct injection engines, the fuel is (partially) superheated for a significant proportion of the time during operation. This means that the vapour pressure of the fuel, or at least of many of its components, is higher than the ambient pressure inside the engine during injection. If the excess fuel enthalpy cannot be removed by evaporation at the free surface of the spray, the liquid phase boiling creates new surfaces. This phenomenon is known as flash boiling. Flash-boiling atomization produces smaller droplets and can therefore be beneficial as an additional atomization mechanism. Furthermore, it can reduce the penetration depth of a spray, although it also decreases the stability of fuel sprays. This is manifested in undesired targeting changes, that is, spray contraction due to jet-to-jet interaction. In extreme cases, a complete spray collapse can occur, where a multi-hole or hollow-cone spray contracts towards the spray axis and forms a jet-like structure that increases penetration depth. To understand the relationship between flash-boiling atomization and targeting changes, flash boiling was investigated with a single-hole generic injector without jet-to-jet interaction. In addition to macroscopic spray parameters, this study also focused on the flow field of the spray itself measured using laser Doppler anemometry, as well as the spray-induced flow field of the surrounding gas phase measured using fluorescent particle image velocimetry. The results show a strong radial expansion of the jet directly after nozzle exit, caused by internal flash boiling. It is shown that this expansion is caused by a zone of expanding fuel vapour in the centre of the spray. As a result, the displacement of air after injector opening as well as at the front of the spray is significantly increased, causing a decrease in spray front velocity and penetration depth. The stationary air entrainment, however, is only moderately increased as is the total amount of captured air, since the fuel vapour displaces air in the spray.

Fuel-efficient aftertreatment thermal management in modern diesel engines is a difficult challenge, especially during low-load operation. This study explores the performance of cylinder deactivation in a diesel engine during low-load operation following highway cruise through experimental evaluation of two drive cycles, specifically extended idle and repeated heavy heavy-duty diesel truck creep cycles. Cylinder deactivation operations are shown to maintain comparable aftertreatment thermal management performance to conventional thermal management operation while reducing fuel up to 40% during extended idle operation. This fuel efficiency improvement coincides with engine-out emission reductions of 72% for soot and 52% for NOx. Cylinder deactivation also shows improved thermal management compared to a more fuel-efficient conventional operation.

High pressure common rail system is the state-of-the art technology for modern diesel engines to achieve energy conservation and emission reduction. The economy and emission performance of the diesel engines are influenced by the fuel injection stability of the high pressure common rail system. In this work, a high pressure common rail injector numerical model based on bond graph theory has been proposed. The comparisons between experimental results and numerical simulations show that the numerical model could reasonably predict the injection characteristics of the system. In order to reveal the essential rules and inherent characteristics of the fuel injection stability for high pressure common rail system, the rank variations of the state matrix at different injection pulse widths during fuel injection are obtained by means of a linear analysis. In addition, the distributions of eigenvalues for the state matrix in complex plane are investigated using Lyapunov method. The results show that the rank is influenced mainly by the movements of control valve and needle. Furthermore, the variation rule of the rank is independent of the injection pulse width before the needle is opened. The needle channel orifice of the injector plays a dominant role in transformation of the system from strong damping oscillation to underdamping oscillation. The opening and closing of control valve have significant effect on the stability of the system because its movement breaks the stability, and the movement of needle has remarkable effect on the oscillating characteristics of the system. High pressure common rail system is a complicated time-variant system with unstable pressure relief and strong oscillation injection.

Diesel engines have better fuel consumption efficiency than gasoline engines. To reduce the particle emission in the diesel exhaust, a ceramic filter, called diesel particulate filter, has been developed. Unfortunately, the pressure drop (filter backpressure) continues to increase, resulting in an increase in fuel conversion rate as well as available torque. In order to develop the filter with lower pressure drop, the filter structure is strategically optimized in the design of the filter product. To do so, the information on phenomena during the filtration is needed. This article sets out numerically to study the variation in the pressure drop when the particulates are trapped inside the porous walls of diesel particulate filter. To discuss the flow dynamics and pressure drop caused by the soot deposition, the numerical simulation is purposely conducted in two-dimensional coordinate. This is because the variation in flow channel through pores during the filtration can be visualized easily. Here, eight filters were tested systematically. Utilizing these simulation results, we try to explain the main factors for the pressure drop variation during the filtration. Based on the presented results, it is shown that the flow field is gradually varied during the filtration. The knowledge regarding the well-known pressure drop variation observed in the stage from the depth filtration to the surface filtration is provided.

This article introduces a physical model of a three-way catalytic converter oriented to engine cold-start conditions. Computational cost is an important factor, particularly when the modelling is oriented to the development of engine control strategies. That is why a one-dimensional one-channel real-time capable model is proposed. The present model accounts for two phases, gas and solid, respectively, considering not only the heat transfer by convection between both, but also the water vapour condensation and evaporation in the catalyst brick, which plays a key role during engine cold-start. Moreover, the model addresses the conductive heat flow, heat losses to the environment and exothermic reactions in the solid phase, as well as the convective heat flow in the gas phase. Regarding the chemical model, the oxidation of hydrocarbons and carbon monoxide is considered by means of the Langmuir–Hinshelwood mechanism. Three layers make up the model structure from a kinetic point of view, bulk gas, washcoat pores and noble metal in the catalyst surface. The model takes fuel-to-air ratio, exhaust gas mass flow, temperature, pressure and gas composition as inputs, providing the thermal distribution as well as the species concentration along the converter.

This article describes the design and experimentation of a new anaerobic internal combustion engine using direct injection of liquid monopropellant. Specifically, the use of monopropellant post-injection allows the control of the profile P - V of the cycle, which significantly increases the mean effective pressure (indicated mean effective pressure) and the power density of the engine. The monopropellant used was isopropyl nitrate, which is the first known demonstration of a piston engine using this monopropellant for anaerobic operation. The engine power has been modulated with post-injection strategy to modify the P - V cycle profile to obtain a constant-pressure combustion in anaerobic mode. Experiments were performed using an engine with a single piston with a effective swept volume of 45 cm³, at an operating frequency of 2 Hz. The prototype engine has achieved an indicated mean effective pressure of up to 4.4 MPa and an indicated power up to 400 W. The indicated thermodynamic efficiency of the engine is found to be about 13% based on the isopropyl nitrate heat of explosion. The indicated specific fuel consumption of the engine is 2.5 mg/J, which represents a conversion efficiency of 49% based on the isopropyl nitrate specific energy.

Super-knock has been the main obstacle to improve power density and engine efficiency of modern gasoline engines. Previous researches show that the key points of super-knock are composed of pre-ignition and detonation. The former is the inducement and the latter is the root reason why super-knock could damage engines dramatically. Lots of studies have been conducted to suppress super-knock by eliminating pre-ignition. Using a rapid compression machine, this work explores the lean mixture control strategy to eliminate detonation and thus suppressing super-knock. Furthermore, a one-dimensional simulation model was set up to investigate the mechanism of how lean mixture could suppress detonation and super-knock. The experimental and simulation results show that based on detonation and super-knock operating condition, adding 80% additional air while keeping the same fuel energy density could transfer combustion from detonation mode to super-sonic auto-ignitive deflagration mode. The peak pressure and pressure oscillation could be reduced significantly. This indicates that boosted lean burn could suppress detonation and thus suppress super-knock effectively, even if pre-ignition occurs. It could be an effective and practical control strategy to protect modern highly turbocharged gasoline engines.

This article addresses a real-time optimal control problem of diesel engines. A stochastic model predictive control scheme is presented for the torque control problem of diesel engines where the driver’s demand torque is predicted using traffic information, and the probability distribution is exploited to represent the stochastic characteristics in the driver’s behavior. It will be shown by the simulation validation that the proposed scheme achieves much better performance of emission and energy consumption.

This article presents an experimental and thermodynamic analysis of the direct injection of propane in an optically accessible variant of a downsized production engine. Propane is used as a surrogate for liquefied petroleum gas and is tested at several fuel rail conditions. Imaging of the sprays’ structure is conducted using planar laser Mie scattering. A number of seemingly counter-intuitive trends relating to rail pressure and temperature are observed from the experiments, and thermodynamic investigation is conducted to explain these trends. It is concluded that flash-boiling induced vaporization external to the injector nozzle is largely responsible for the observed behavior, and a new quantity is proposed to describe the severity of this phenomenon.