Cognitive Model of the Internal Combustion Engine

<div class="section abstract"><div class="htmlview paragraph">An Air intake system (AIS) is a duct system which leads the airflow going into the internal combustion engine. Combustion requires oxygen, and the more oxygen is provided into the combustion process the more power it will produce. The lower the air temperature, the higher its density, and hence there is more oxygen in a unit volume. The quality of air entering engine can be measured with the air temperature.</div><div class="htmlview paragraph">AIS design and routing influence the air charge temperature (ACT) at intake manifold runners and ACT is normally measured at AIS throttle body in reality. Higher ACT lead to inefficient combustion and can lead to spark retard. Optimization of AIS designs and reduction of ACT can improve engine performance and vehicle fuel economy.</div><div class="htmlview paragraph">High ACT can be a result of two different phenomena: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Recirculation - Hot air from the underhood environment ingested into the dirty side of the air intake system. This is the result of the AIS snorkel not being isolated or sealed from the engine compartment hot air.</div></li><li class="list-item"><div class="htmlview paragraph">Underhood temperature rise - Air inside AIS is heated by the ducts walls because it is routed through a hot underhood environment. The longer the length and larger the diameter of the air induction system, and the higher duct skin temperatures, the worse the temperature rise.</div></li></ul></div><div class="htmlview paragraph">In this paper, it is planned to simulate and study the effects of following factors on ACT with CFD using a FCA production vehicle: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">Snorkel location: snorkel sucking fresh air at side air guide or snorkel sucking underhood hot recirculation air.</div></li><li class="list-item"><div class="htmlview paragraph">Exhaust hot end at front of an east-west engine or at the rear of the engine; these two arrangements will result in different underhood air temperatures and radiation to AIS surfaces.</div></li><li class="list-item"><div class="htmlview paragraph">Heat shield effects on ACT: heat shield blocks radiation from exhaust system to AIS surfaces, and hence reduces charge air heat pick from AIS duct walls.</div></li><li class="list-item"><div class="htmlview paragraph">The effects of other measures such as cutting holes on hood or fenders to lower engine compartment air temperatures.</div></li></ul></div><div class="htmlview paragraph">Although the airflow in vehicle AIS duct is transient in nature, steady CFD simulations will be performed to study the above cases for simplification, and CFD approach will be discussed in details. Vehicle test data will be used to validate the CFD models.</div><div class="htmlview paragraph">Finally, general practices of AIS development will be discussed, and future work on this topic will be outlined.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Piston rings and cylinder liners are the key components of internal combustion engines (ICEs). Their state has a great influence on the performance of ICEs. The friction and wear of these components directly affect the total power output of ICEs. Therefore it is of great importance to monitor the wear of these components in real time so that a proper maintenance strategy could be implemented to prevent financial misfortune. In the present research work, an effort has been done to detect the running-in wear of piston rings and cylinder liner of a realistic diesel engine in real time. The system comprises a magneto-resistive (MR) sensor and a permanent magnet. The wear of piston rings and cylinder liner were on-line monitored using the MR sensor. The surface roughness, weight loss, engine performance, and emission parameters were also measured. Further, the experimental results were validated with the numerical simulation results using COMSOL Multiphysics 5.0. These results showed the potential application of the sensor to detect the wear of piston rings and cylinder liner. Further, the obtained results provide a good correlation between the magnetic field strength variation and other parameters such as surface roughness, weight loss, performance, and emission of the engine. The outcomes of the present investigations may help automotive, marine, and locomotives industries to detect the wear of piston rings and cylinder liner in real time.</div></div>

<div class="section abstract"><div class="htmlview paragraph">In the last six decades, due to the continuous improvement in environmental legislations and depletion of fossil fuels in the world, IC engine researchers have been vigorously exploring various possibilities of reducing petroleum fuel dependency and emissions of internal combustion (IC) engines. Operating IC engines in low heat rejection (LHR) mode by providing thermal barrier coating (TBC) to some of the engine components is one of the methods to improve thermal efficiency and reduce some of the tailpipe emissions. Yttria stabilized zirconia (YSZ) is a commonly used TBC material in IC engines due to its thermal characteristics. On the other hand, running an engine in a dual-fuel operation by a gaseous fuel gives better and more efficient combustion. In this research work, an attempt was made to study the combined effects of running a compression ignition (CI) engine in dual-fuel operation with LHR mode on its performance, and emissions were investigated. For this purpose, a 4.4 kW, four-stroke, naturally aspirated, single-cylinder, direct injection (DI) diesel engine was converted to run in dual-fuel mode. Two pistons were used in this study; one is uncoated and the other one was coated. The second piston was coated by 300μm thickness with a ceramic composition of ZrO<sub>2</sub> and 6-8 wt% Y<sub>2</sub>O<sub>3</sub> ceramic material called as YSZ. A blend of Jatropha methyl ester (JME) with diesel in the respective proportion of 20% and 80% was prepared (JME20) and was used as pilot fuel, and the oxy-hydrogen (HHO) gas was used as inducted fuel for dual-fuel operation. The HHO gas is a carbon-free, hydrogen-based renewable fuel that is produced by the process of water electrolysis in a fabricated wet cell electrolyzer. The results indicated that the YSZ coated piston engine in both the dual-fuel operations (i.e) D100+HHO, and Opt.JME20+HHO showed thermal efficiency higher by about 5.5% and 5.9% compared to that of D100 operation at full load. The same dual-fuel operations also showed a reduction of HC, CO, and smoke irrespective of the engine load. The maximum HC, CO, and smoke emissions were reduced by about 38.2%, 40%, and 20.4% respectively for Opt.JME20+HHO with the YSZ coated piston engine compared to baseline data at full load.</div></div>

<div class="htmlview paragraph">Controlled Auto-Ignition (CAI) combustion, also known as HCCI or PCCI, has recently emerged as a viable alternative combustion process to the conventional spark ignition (SI) or compression ignition (CI) process for internal combustion (IC) engines, owing to its potential for high efficiency and extremely low emissions. One of the most effective and practical means of achieving CAI combustion in an engine is to retain or recycle the burnt gases. In order to understand better the effects of recycled burnt gases on CAI combustion, detailed analytical and experimental studies have been carried out. The analytical studies were performed using an engine simulation model with detailed chemical kinetics.</div> <div class="htmlview paragraph">The five effects of the recycled burned gases studied include:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">Charge heating effect: higher intake charge temperature due to hot burned gases;</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">Dilution effect: the reduction of oxygen due to the presence of the burned gases;</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">Heat capacity effect: due to higher specific heat capacity of burned gases;</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">Chemical effect: chemical reactions involving CO<sub>2</sub> and H<sub>2</sub>O in the burned gases</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">Stratification effect: recycled burned gases are stratified from the fuel/air mixture.</div></li> </ol> </div> <div class="htmlview paragraph">And the main conclusions are:</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1.)</span><div class="htmlview paragraph">The charge heating effect is mainly responsible for the advanced AI timing due to hot burned gases. It increases the heat release rate and shortens the combustion duration.</div></li> <li class="list-item"><span class="li-label">(2.)</span><div class="htmlview paragraph">The dilution effect does not affect AI timing, but it extends combustion duration. Its slows down the heat release rate only when large amount of burned gases is present.</div></li> <li class="list-item"><span class="li-label">(3.)</span><div class="htmlview paragraph">The heat capacity effect is mainly responsible for the reduction in the heat release rate, and it has a similar effect to extend the combustion duration as the dilution effect.</div></li> <li class="list-item"><span class="li-label">(4.)</span><div class="htmlview paragraph">The chemical effect does not affect AI timing and heat release rate. It reduces the combustion duration slightly at high concentrations of burned gases.</div></li> <li class="list-item"><span class="li-label">(5.)</span><div class="htmlview paragraph">The stratified burned gases facilitate the CAI combustion due to the presence of higher temperature region at the boundary between of the hot burned gases and combustible charge.</div></li> </ol> </div>

<div class="htmlview paragraph">This report describes the possibility of quantitative analysis of Schlieren photographs as an internal combustion engine diagnostic.</div> <div class="htmlview paragraph">Using a recently developed photographic analysis system, it was attempted to analyze Schlieren photographs. Results showed simple integration calculations produced significant distortion in the analyzed results. To eliminate the distortion, some correction techniques were developed in this research. Accuracy of the analyzed results were evaluated roughly with uncertainty analysis. The results showed that this analysis technique can be one of the approximate diagnostics for the measurement of fuel vapor and density distribution in internal combustion engine research.</div> <div class="htmlview paragraph"><b>SCHLIEREN</b> photography is one of the most popular visualization techniques in the research of internal combustion engines. Although the photographs have density information in themselves, they are used mainly for the purpose of qualitative visualization. The objective of this research is to develop a quantitative analysis of Schlieren photographs for internal combustion engine research.</div> <div class="htmlview paragraph">One important parameter in engine research, for example, is the air entrainment in fuel jet vapor. Its measurement has previously been possible by gas sampling, laser holography, or laser Raman spectroscopy. The gas sampling method provides only point data, and the laser methods are very sensitive to vibration or optical settings. With this present Schlieren photographic analysis technique, it will be possible to measure instantaneously the whole space of the density field with a very simple optical system which is commonly used in engine research. Lakshminarayan and Dent(<span class="xref">1</span>)<span class="xref">*</span> analyzed interferometric photographs of jet sprays impinging on a wall. A major part of their (analysis method involved the counting of fringes which are sometimes difficult to distinguish in photographs. Nishida et al.(<span class="xref">2</span>)(<span class="xref">3</span>) analyzed Schlieren photographs reconstructed from laser holograms of jet vapor. However, they did not refer to the accuracy of the results.</div> <div class="htmlview paragraph">This report describes the background of the quantitative analysis and shows some analyzed results. The analysis was made for a CO2 jet injected into air. The Schlieren photographs were analyzed by an image processor and a personal computer.</div> <div class="htmlview paragraph">The results showed that the elimination of integrated error due to non-uniform background level was one of the most important parameters to be considered. In this study, a correction method is shown to determine the non-uniform background level and also to improve the accuracy of the results. This report also describes analyzed results for transient free jets and wall-impinging jets, which were compared with experimental results.</div>

<div class="section abstract"><div class="htmlview paragraph">The air-fuel mixture formation in an optical direct-injection internal combustion engine is investigated by numerical simulations for the two biofuels Ethanol and 2-Butanone. The gas phase in the internal combustion (IC) engine is predicted by a large-eddy simulation, in which the fuel phase is determined by a spray model based on Lagrangian particle tracking. A hollow-cone injector is used for which the primary breakup is modeled by a series of small full-cone injections, while the Rosin-Rammler initial droplet size distribution is used. The secondary spray break-up is modeled by the Kelvin-Helmholtz-Rayleigh-Taylor (KHRT) model, and the evaporation of the fuel is determined by the Bellan-Harstad model. The gas phase simulation is based on a finite-volume method formulated for hierarchical Cartesian grids, in which the immersed moving boundaries are resolved using a multiple level-set/cut-cell approach. Characteristic boundary conditions are used to avoid artificial reflections at the inlet and outlet ports. Approximately 50 million mesh cells are used to resolve the in-cylinder flow domain. Dynamic load balancing is utilized to redistribute the workload due to grid adaptation, moving valves and piston, as well as fuel droplets. The validation of the spray model is performed by comparison of the numerical findings with pressure chamber measurements.</div><div class="htmlview paragraph">Good agreement is obtained for the spray penetration and droplet size distribution. Measurements of the in-cylinder flow-field in an optical engine are used to validate the flow field simulation results in the IC engine. The simulation of the mixture formation for the biofuels show that the difference of the evaporation rate between Ethanol and 2-Butanone leads to significant differences in the spray behavior. While wall impingement is a significant factor with Ethanol, this effect is negligible for 2-Butanone. The higher evaporation rate of 2-Butanone results in a less favorable mixture formation due to the lower liquid penetration of the spray.</div></div>

<div class="section abstract"><div class="htmlview paragraph">One of the practical consequences of the development of low CO₂ emission cars is that many of the traditional NVH sound engineering processes no longer apply and must be revisited.</div><div class="htmlview paragraph">Different and new sound sources, new constraints on vehicle body design (e.g., due to weight) and new sound perception characteristics make that the NVH knowledge built on generations of internal combustion-powered vehicles cannot be simply transferred to Hybrid and Electric Vehicles (HEV). Hence, the applicability of tools must be reviewed and extensions need to be developed where necessary.</div><div class="htmlview paragraph">This paper focuses on sound synthesis tools as developed for ICE-powered vehicles. Because of the missing masking effect and the missing intake and exhaust noise of the Internal Combustion Engine (ICE) in electric vehicles, on one hand electric vehicles are quieter than traditional vehicles. On the other hand, other components such as HVAC system, alternator, vacuum pump, power-steering pump, cooling systems, transmission systems, inverter noise, etc., become more important and generate new complex sound signatures. Typically, their interior noise is well-defined by high-frequency noise components which can be subjectively experienced as annoying, hence the increased importance put to sound quality aspects and perceptual-relevant NVH studies.</div><div class="htmlview paragraph">In the paper, a Virtual Car Sound (VCS) synthesis technique for HEV is designed. This approach turns out to be a very helpful engineering tool to design a brand specific sound and allows reproducing typical sound features of HEV during real-time driving simulation based on a Sound Quality Equivalent Model (SQE). Several SQE models were constructed for different powertrains of HEV in various engine conditions. Finally, the results of the sound metrics and listening tests indicate a comparison between the synthesized sounds and the original sound recordings.</div></div>

<div class="htmlview paragraph">As the community is becoming more and more aware and conscious of the pollution problems caused by the internal combustion engine and its use in transportation, we are now seeing the first projects and prototypes regarding hybrid and electrically-powered vehicles.</div> <div class="htmlview paragraph">One of the main problems witnessed by engineers has been that of the relatively low operating range provided by the storage batteries available on the market today, and so, recovering the energy that is inevitably lost during braking is of primary importance.</div> <div class="htmlview paragraph">The concept of regenerative braking is fairly simple as it consists in making the electric motors function as generators.</div> <div class="htmlview paragraph">In many of today's applications we find two indipendent controls for the operation of the hydraulic brake and for the activation of regenerative braking. The choice on which braking mode to use, or in which sequence the two modes are to be used is left to the driver who, at the onset of braking, is forced to make mental considerations in order to activate the two braking modes in the right sequence. Furthermore, the driver must not forget to disable the regenerative function at the end of each stop.</div> <div class="htmlview paragraph">BREMBO has designed a braking system in which a single control, that is, the brake pedal, activates and disables in the right sequence the two different braking modes, thus allowing:</div> <div class="htmlview paragraph"> <ul class="list disc"> <li class="list-item"> <div class="htmlview paragraph">to maximize energy recovery by the electric motors each time the driver steps on the brake pedal;</div> </li> <li class="list-item"> <div class="htmlview paragraph">the hydraulic brake to be used in addition to regenerative braking when the latter is not enough to produce the required deceleration.</div> </li> </ul> </div> <div class="htmlview paragraph">The proposed braking system is lightweight and versatile. It can be adapted to the different powertrain configurations seen on various electric vehicles.</div>

<div class="section abstract"><div class="htmlview paragraph">The Deep Orange program immerses automotive engineering students into the world of an OEM as part of their 2-year graduate education. In support of developing the program’s seventh vehicle concept, the students studied the sponsoring brand essence, conducted market research, and made a heuristic assessment of competitor vehicles. The upfront research lead to the definition of target customers and setting vehicle level targets that were broken down into requirements to develop various vehicle sub-systems.</div><div class="htmlview paragraph">The powertrain team was challenged to develop a scalable propulsion concept enabled by a common vehicle architecture that allowed future customers to select (at the point of purchase) among various levels of electrification best suiting their needs and personal desires. Four different configurations were identified and developed: all-electric, two plug-in hybrid electric configurations, and an internal combustion engine only.</div><div class="htmlview paragraph">The electrified powertrain comprises of an innovative thermal system using the structural rocker beams as heat exchangers, thereby eliminating the need for conventional radiators. Two cargo compartments (one at each end of the vehicle) were realized through efficient packaging of the electric units and an internal combustion engine in the front and rear, respectively, with a modular energy (battery and/or fossil fuel) storage system located under the passenger compartment. Simulation tools were used to size the powertrain components for each of the four propulsion configurations. The efficiency of the thermal system was verified using CFD analyses in combination with preliminary bench testing.</div><div class="htmlview paragraph">The outcome of the Deep Orange 7 project was a drivable vehicle demonstrator designed, engineered, built and tested by the student team. Industry partners functioned as project sponsors as well as mentors throughout the 2-year development cycle.</div></div>

<div class="htmlview paragraph">Alternative powertrain configurations such as hybrid electric vehicles and fuel cell vehicles seem to be the best response to the need of reduced pollutant emissions, especially in urban areas, and to meet future emission limits, that appear to be very severe targets for traditional technologies.</div> <div class="htmlview paragraph">In hybrid electric vehicles (HEVs) an internal combustion engine is combined with one or more electric machines, with the aim of extending the range of the electric and making the entire vehicle more energy–efficient. The architecture of a hybrid drive train is complex, comprising at least two different energy conversion devices (i.e. internal combustion engine and electric machine) drawing energy from at least two different energy storage devices (i.e. fuel tank and battery). Moreover, complex control strategies must be defined in order to properly control the division of load between the thermal engine and the electric machines.</div> <div class="htmlview paragraph">To meet increasing global competition, which means reducing lead-time and costs for hybrid vehicles design, it is necessary to develop methods that wouldquickly evaluate various design concepts. Even if many computational models are available to simulate the performances of HEVs, there’s still a lack of generalized mathematical analyses.</div> <div class="htmlview paragraph">An analytical model has been developed in order to study power flows in hybrid vehicle drive trains. The mathematical formulation allows a quick analysis of the complete energy cascade from fuel energy to tractive power, comprising electricity generation and consumption and energy recovery from braking. As a result a general formulation of the total tractive energy and of the global efficiency of hybrid electric vehicles in function of the main characteristics of its components is provided.</div> <div class="htmlview paragraph">The goal of the analytical model is to enable a quick exploration of design possibilities of hybrid powertrains. Some results are presented in order to show how the present model allows a quick insight into the effects of the main system characteristics on the power flows and the corresponding component losses of the drive train.</div>

<div class="section abstract"><div class="htmlview paragraph">The increasing demand for environmentally friendly and fuel-efficient transportation and power generation requires further optimization and minimization of friction power losses. With up to 50% of the overall friction, the piston cylinder unit (PCU) shows most potential within the internal combustion engine (ICE) to increase mechanical efficiency. Calculating friction of internal combustion engines, especially the friction contribution from piston rings and skirt, requires detailed knowledge of the dynamics and lubrication regime of the components being in contact. Part I of this research presents a successful match of simulated and measured piston inter-ring pressures at numerous operation points [<span class="xref">1</span>] and constitutes the starting point for the comparison of simulated and measured piston group friction forces as presented in this research.</div><div class="htmlview paragraph">The authors utilized a single-cylinder floating-liner engine (FLE), based on a heavy-duty diesel truck engine, to determine crank angle resolved friction of the piston cylinder unit. The temperatures of the PCU were measured, and surface temperature distribution and thermal deformation were calculated to ensure realistic oil viscosity and piston and liner deformation under operating condition within the friction simulation.</div><div class="htmlview paragraph">Friction measurements were conducted under motored and fired engine condition. To derive the friction contribution of each ring and the piston skirt separately, motored strip-down tests were conducted as well. Piston ring friction was simulated with a validated ring dynamic simulation tool in combination with flow simulations of the surfaces using a deterministic correlation approach. To consider friction properly within the simulation, high-quality surface representation is needed. Precise optical three-dimensional measurements of the cylinder liner surface and the artificially surface generation for accurate numerical surface representation without measurement errors, revealed to be key. With the simulation model the friction contribution of each ring was compared separately with the strip-down measurement. Moreover, the piston secondary motion and the friction behavior of the piston skirt was calculated and compared to the measurements as well. As a result, the overall friction of the PCU was compared for motored and fired condition. The friction mean effective pressure (FMEP) as well as the crank-angle resolved friction forces from measurement and simulation were analyzed in detail. The comparison between simulation and FLE measurement was done for engine speeds from 10 to 1500 rpm, at oil temperatures from 40° to 100° C and engine loads up to 15.5 bar IMEP (indicated mean effective pressure).</div><div class="htmlview paragraph">The friction contribution (FMEP) of the simulation and measurement matches very well. The detailed examination of the crank angle resolved friction forces shows very good correlation for the hydrodynamic, and boundary lubrication regions.</div><div class="htmlview paragraph">This research successfully proves the ability to predict the friction forces and power losses of the different components of the PCU in combination with honed cylinder liners. It also reveals the importance of the quality of the input parameters such as surface topographies, surface temperatures respectively thermal deformations, oil parameters and contact geometries. Reliable input in combination with experimental data for the validation of the simulation models, enables the utilization of the simulation tools for reliable predictive design approaches.</div></div>

<div class="section abstract"><div class="htmlview paragraph">The main objective of this work is to describe the approach used and the results achieved on test bench, specifically for the piston design and development, which supports efficiency demonstration for a new class of internal combustion engine.</div><div class="htmlview paragraph">In this era of ICE revolution rather than evolution, although the piston function remains the same, the working boundary conditions are drastically changing, and the development time is often compressed in favor of a shorter time to market.</div><div class="htmlview paragraph">In this paper, piston requirements, functions, design and testing results from a development program on a Heavy Duty Recuperated Split Cycle Engine are reported. This includes the strategy for a fast and cost-efficient modification of the compression/expansion ratio, the technology and the materials used for reduction of heat losses, and a thermal expansion study, which supports material selection for the structure and the thermal barrier coating, to optimize piston function.</div><div class="htmlview paragraph">This work is based on available information, requirements, hypothesis & problem simplification, supported by virtual validation, FEM analysis, spreadsheet calculation, component specifications and performance leading to the final piston design.</div><div class="htmlview paragraph">This work includes the development done on suppliers’ side in order to fulfil the project requirements, the tradeoff between technology selection and the pressing need to respect an extremely short time frame for parts procurement.</div><div class="htmlview paragraph">This work is referring to a specific component, but the methodology described in this paper has been generally developed for the new class of ICE and can be successfully applied to other base engine components about the common key points (time to market, fuel efficiency, development costs).</div></div>

<div class="section abstract"><div class="htmlview paragraph">Ammonia is a zero-carbon candidate fuel for the decarbonization of internal combustion (IC) engines. A concern when using ammonia in IC engines is the increased emissions of nitrogen oxides (NO<sub>X</sub>), due to the additional nitrogen in the ammonia molecule. Compared to conventional petroleum such as gasoline and diesel, ammonia combustion adds the fuel NO<sub>X</sub> formation mechanism in addition to the original thermal NO<sub>X</sub> generation pathway, which further complicates the NO<sub>X</sub> emission characteristics of ammonia engines. Decoupling fuel NO<sub>X</sub> and thermal NO<sub>X</sub> helps to increase the understanding of the formation and evolutionary characteristics of nitrogen oxides occurring inside ammonia engines, but the available literature lacks studies in this respect. The purpose of this study is to fill this research gap and to propose a methodology for decoupling fuel NO<sub>X</sub> and thermal NO<sub>X</sub>. In brief, an artificial elemental nitrogen is applied to the Zeldovich mechanism and to the diatomic nitrogen in the combustion air, which allows the formation of NO<sub>X</sub> from the elemental nitrogen in the ammonia fuel to be separated from the NO<sub>X</sub> formed from the nitrogen in the air. A three dimensional (3D) computational fluid dynamics (CFD) model demonstrates the effectiveness of this approach and investigates the spatial and temporal distribution characteristics of thermal NO<sub>X</sub> and fuel NO<sub>X</sub> in the turbulent combustion field of ammonia engines. The in-cylinder activity analysis suggests that this separation of the NO<sub>X</sub> formation mechanism slightly alters the nitrogen-based chemistry, which is unavoidable. However, this approach still allows a reasonable characterization of the formation and evolution of fuel NO<sub>X</sub> and thermal NO<sub>X</sub>. The simulations show that fuel NO<sub>X</sub> is formed during ammonia oxidation because fuel NO<sub>X</sub> is an intermediate species, while thermal NO<sub>X</sub> has a high concentration in the burned zone because it is related to the temperature and the residence time of nitrogen at that temperature, both of which are expected and support the successful decoupling of fuel and atmospheric nitrogen. In addition, nitrous oxide (N<sub>2</sub>O) emissions come from the fuel NO<sub>X</sub> mechanism and are mainly distributed along the liner walls as it is formed by partial oxidation of ammonia released from the crevices during the late oxidation process. Moreover, the concentrations of both thermal and fuel-based nitrogen monoxide vary with the chemical equilibrium that changes with piston motion, and their concentrations are always comparable. As a result, combustion strategies for ammonia internal combustion engines needs to consider both thermal and fuel NO<sub>X</sub> reduction mechanisms, where the main difficulty is the N<sub>2</sub>O reduction. Catalytic combustion mode may be a viable strategy to improve the oxidation efficiency of the ammonia fuel trapped in the crevice and reduce N<sub>2</sub>O emissions in the cylinder.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Internal combustion (IC) engines are the most common power unit technology found in road vehicles. The process of combustion within IC engines is linked to the output torque and overall powertrain performance. This work presents a method of analysing the parameters of cylinder pressure and crankshaft instantaneous speed signals obtained from a turbocharged, 4-stroke, 4-cylinder, 1.6 Litre, spark ignition, gasoline direct injection engine at various speed and load operating conditions. Whereas cepstrum analysis is used in the present work to extract critical features characterising the combustion process. Cepstrum analysis showed that the location of maximum heat release can be directly obtained from the quefrency of the instantaneous crank speed. This paper presents a systematic scheme for applying cepstrum for obtaining combustion features from the instantaneous crank speed signal.</div></div>

<div class="section abstract"><div class="htmlview paragraph">Internal combustion (IC) engines still power most of the vehicles on road and will likely to remain so in the near future, especially for heavy duty applications in which electrification is typically more challenging. Therefore, continued improvements on IC engines in terms of efficiency and longevity are necessary for a more sustainable transportation sector. Two important design objectives for heavy duty engines with wet liners are to reduce friction loss and to lower the risks of cavitation damages, both of which can be greatly influenced by the piston-liner clearance and the design of the piston skirt. However, engine design optimization is difficult due to the nonlinear interactions between the key design variables and the design objectives, as well as the multi-physics and multi-scale nature of the mechanisms that are relevant to the design objectives. In this work, an efficient optimization method is proposed to optimize the piston skirt design and the piston-liner warm clearance with respect to the aforementioned objectives, subject to design constraints. The method couples a neural network surrogate of a high-fidelity numerical model for piston secondary motion, which can accurately predict the objective values corresponding to different piston skirt designs and piston-liner clearances, with genetic algorithms to seek designs that can achieve a good tradeoff between the two objectives, while having a reasonable computation cost. Results show that with the proposed method, the optimal skirt design can have up to 62% lower risk of cavitation damage and up to 42% lower friction loss compared to the baseline design while satisfying important design constraints.</div></div>