Hypersonic flight vehicles have potential applications in strategic defence, space missions, and future civilian high-speed transportation systems. However, structural integration has significant challenges due to extreme aero-thermo-mechanical coupled effects. Scramjet-powered air-breathing hypersonic vehicles experience extreme heat loads induced by combustion, shock waves and viscous heat dissipation. An active cooling thermal protection system for scramjet applications has the highest potential for thermal load management, especially for long-duration flights, considering the weight penalty associated with the heavier passive thermal insulation structures. We consider the case of active cooling of scramjet engine structural walls with endothermic hydrocarbon fuel. We have developed a semi-analytical one-dimensional heat transfer model considering a prismatic core single cooling channel segment as a representative volume element (RVE) to analyse larger scale problems.
The combustion of fossil-based fuels in ICEs, resulting in a huge amount of greenhouse gases (GHG) and leading to an immense global temperature rise, are the root causes of the more stringent emission legislations to safeguard health and that encourage further investigations on alternative carbon-neutral fuels. In this respect, the hydrogen has been considered as one of the potential clean fuels because of its zero-carbon nature. The current development of hydrogen-based ICEs focuses on the direct injection (DI) strategy as it allows better engine efficiency than the port fuel injection one. The fuel jet behavior is a fundamental aspect of the in-cylinder air-fuel mixing ratio, affecting the combustion process, the engine performances, and the pollutants emissions. In the present study, comprehensive investigations on the hydrogen jet behavior, generated by a Compressed Hydrogen Gas (CHG) outward opening injector under different operative conditions, were performed.
A major concern for a high-power density, heavy-duty engine is the durability of its components, which are subjected to high thermal loads from combustion. The thermal loads from combustion are unsteady and exhibit strong spatial gradients. Experimental techniques to characterize these thermal loads at high load conditions on a moving component such as the piston are challenging and expensive due to mechanical limitations. High performance computing has improved the capability of numerical techniques to predict these thermal loads with considerable accuracy. High-fidelity simulation techniques such as three-dimensional computational fluid dynamics and finite element thermal analysis were coupled offline and iterated by exchanging boundary conditions to predict the crank angle-resolved convective heat flux and surface temperature distribution on the piston of a heavy-duty diesel engine.
This study investigates the impact of hydrogen energy share and excess air ratio on the combustion characteristics of an ammonia-hydrogen jet ignition engine at compression ratios of 11.5 and 17.3 under 800 rpm and approximately 6 bar IMEP. The results indicate that, when passive jet ignition is used for both compression ratio conditions, a high hydrogen energy share is required to achieve stable combustion and high indicated thermal efficiency. Specifically, at the compression ratio of 11.5, a higher ammonia concentration is needed for stable combustion compared to the compression ratio of 17.3. Additionally, the range of excess air for stable combustion is narrower at the compression ratio of 17.3. The use of hydrogen as the auxiliary fuel for active jet ignition significantly reduces the overall hydrogen energy share required to achieve stable combustion.
The continuous improvement of spray-ignition direction-injection (SIDI) engines is largely attributed to the enhanced understanding of air-fuel mixing and combustion processes. The intricate interaction between transient spray behavior and the ambient flow field is important to unveil the airflow dynamics during the spray injection process. This study investigates the fuel-spray boundary interactions under different superheated conditions by analyzing the ambient flow field pattern with constraint-based modeling (CBM). In the experimental setup, superheated conditions are facilitated by adjusting different fuel temperatures and ambient pressures. By adding the tracer particles containing Rhodamine 6G to the ambient air, the combined diagnostic of fluorescent particle image velocimetry (FPIV) and Mie-scattering is implemented to measure the velocity distribution and flow trajectory of the air surrounding the spray formation and propagation.
With the increasing demands to reduce the carbon footprint and emissions, engines powered by e-fuels offer a possibility for sustainable transportation solutions. This work focuses on the effect of exhaust gas rebreathing and external EGR (Exhaust Gas Recirculation) in a CNG (Compressed Natural Gas)-OME (Polyoxymethylene Ether) dual-fuel engine. A four-cylinder heavy-duty engine was used to conduct the engine tests at different load points from 1100rpm to 1600 rpm and 4.9 to 14.7 bar brake mean effective pressure (BMEP). The quantities of the high (HRF) and the low reactivity fuel (LRF) were varied, as were the external and internal EGR rates and their combination. CNG was injected into the intake manifold to create a homogeneous air-fuel mixture, while OME was introduced as a pilot injection directly into the combustion chamber. Results show an increase in THC and CO emissions, while NOx emissions are significantly reduced compared to diesel operation.
Amid rising demands for fuel efficiency and emissions reduction, enhancing the thermal efficiency of gasoline engines has become imperative, which requires higher efficiency combustion strategies and integrated optimized design to maximize the work output from fuel. In gasoline engines, both increasing the compression ratio and using lean burn mode improve the thermal efficiency effectively. Although there is limited scope for increasing the compression ratio due to the higher sensitivity to knocking, especially under stoichiometric conditions, reduced sensitivity could be got with leaner mixture fill into cylinder, which can further increase the specific heat ratio and thermal efficiency. However, realizing the efficiency benefits of lean burn in gasoline engines necessitates overcoming critical challenges like ensuring robust ignition process and accelerating burning rates to achieve short, stable combustion durations.
It is widely recognized that internal combustion engines (ICE) are needed for global transport for years to come, however, demands on ICE fuel efficiency, emissions, cost, and performance are extremely challenging. Gasoline compression ignition (GCI) is one approach to achieving demanding efficiency and emissions targets. At Aramco Research Center-Detroit, an advanced, multi-cylinder GCI engine was designed and built using the latest combustion system, engine controls, and lean aftertreatment. The combustion system uses Aramco's PPCI-diffusion process for ultra-low NOx and smoke. A P2 48V mild hybrid system was integrated on the engine for braking energy recovery and improved cold starts. For robust low-load operation, a 2-step valvetrain system was used for exhaust rebreathing. The fuel injection system was a modified diesel system with high injection rate and 2000 bar pressure rating.
This study experimentally investigates the combustion stability in RCCI engines along with the gaseous (regulated and unregulated) and particle emissions. Multifractal analysis is used to characterize the cyclic combustion variations in the combustion parameters (such as IMEP, CA50, Pmax) of the RCCI engine. The investigation is carried out on a modified single-cylinder diesel engine to operate in RCCI combustion mode. The RCCI combustion mode is tested for different fuel premixing ratio (r_p) and diesel injection timing (SOI) at fixed engine speed (1500rpm) and load (1.5 bar BMEP). The particle number characteristics and gaseous emissions are measured using a differential mobility spectrometer (DMS500) and Fourier Transform Infrared Spectroscopy (FTIR) along with Flame Ionizing Detector (FID), respectively. The results indicate that the NOx emissions decrease with advanced SOI while the methane (CH4) emission increases.
Due to increasingly strict emission regulations, the demand for internal combustion engine performance has enhanced. Combustion stability is one of the main research focuses due to its impacts on the emission level. Moreover, the combustion instability becomes more significant under the lean combustion concept, which is an essential direction of internal combustion engine development. The combustion instability is represented as the cycle-to-cycle variation. This paper presents a quasi-dimensional model system for solving the cycle-to-cycle variation in 0D/1D simulation. The modeling is based on the cause-and-effect chain of cycle-to-cycle variation of spark ignition engines, which is established through the flow field analysis of large eddy simulation results. In the model system, varying parameters are turbulent kinetic energy, the distribution of air-to-fuel equivalence ratio, and the in-cylinder velocity field.
An experimental study of the spark ignition process for SI engines was conducted to study spark plug erosion and its effect on breakdown voltage and electrode wear characteristics. The experiments were conducted outside of an engine, in both a pressurized constant volume optical chamber and in a high-pressure vessel heated within a furnace with gas temperatures as high as 700C. J-gap spark plugs designed for natural gas engines were studied at elevated temperature and under a range of pressures to investigate electrode wear characteristics. Both iridium-alloy and platinum-alloy electrode cathode and anode spark plugs were investigated. In addition, single spark events were performed on polished platinum cathode surfaces to allow the visualization of craters from individual spark events in order to quantify how their size and shape were affected by energy deposition and breakdown characteristics.
The passive pre-chamber is valued for its jet ignition and is widely used in the field of gasoline direct injection (GDI) for small passenger cars, which can improve the performance of lean combustion. However, the scavenging and ignition combustion stability of the engine at low speed is a shortcoming that has not been overcome. Simply changing the structural design to increase the fluidity of MC and PC may lead to a reduction in jet ignition performance, which in turn will affect engine dynamics. This investigation is based on a non-uniformly nozzles distributed passive pre-chamber, which is adjusted according to the working fluid exchange between PC and MC. The advantages and disadvantages of the ignition mode of PC and SI in the target engine speed range are compared through optical experiments on a small single cylinder GDI engine. The results show that with the increase of λ from 1.0 to 1.6, the promotion effect of PCJI on load performance gradually decreases.
Ammonia (NH3), a zero-carbon fuel, has great potential for internal combustion engine development. However, its high ignition energy, low laminar burning velocity, a narrow range of flammability limits, and high latent heat of vaporization are not conducive for engine application. This paper numerically investigates the feasibility of utilizing ammonia in a heavy-duty diesel engine, specifically through the method of low-pressure direct injection (LP-DI) of hydrogen to ignite ammonia combustion. The study compares the engine's combustion and emission performance by optimizing four critical parameters: excess air ratio, hydrogen blending ratio, ignition timing, and hydrogen injection timing. The results reveal that excessively high hydrogen blending ratios lead to an advanced combustion phase, resulting in a reduction in indicated thermal efficiency.
Engine knock is a major barrier to achieving higher engine efficiency by increasing the compression ratio of the engine. It is an abnormal event caused by the autoignition of air-fuel mixture ahead of the propagating flame front. A higher octane number fuel can be a good solution to reduce or eliminate the higher knock intensity and obtain better engine performance. Methanol is a promising alternative fuel, which has a higher octane number and can be produced from conventional and non-conventional energy resources to reduce pollutant emissions. This study compares the combustion characteristics of gasoline and methanol fuels in an optical spark-ignition engine using multiple spark plugs. The experiment was performed on a single-cylinder four-stroke optical engine. A customized metal liner equipped with four circumferential spark plugs was used to generate multiple flame kernels inside the combustion chamber.
A potential route to reduce CO2 emissions from heavy-duty trucks is to combine low-carbon fuels and vehicle electrification/hybridization. Hybridization offers the potential to downsize the engine. Although engine downsizing in the light-duty sector can offer significant fuel economy savings mainly due to increased part-load efficiency, its benefits and downsides in heavy-duty engines are less clear. As there has been limited published research in this area to date, there is a lack of a standardized engine downsizing procedure. This paper aims to use an experimentally validated one-dimensional phenomenological combustion model in a commercial engine simulation software GT-Power alongside turbocharger scaling methods to develop downsized engines from a baseline 6-cylinder (2.2 L/cyl, 26 kW/L) pilot-ignition, direct-injection natural gas engine.
This paper presents a feedback control strategy to minimize noise during dog clutch engagement in a hybrid transmission. The hybrid transmission contains an internal combustion engine(ICE) and 2 electric motors in P1 and P3 configurations. For efficiency during driving, at high vehicle speeds ICE is connected to wheels, via the dog clutch, hence shifting the vehicle from series to parallel hybrid mode. It is shown by experimental results that if the speed difference between the two sides of the dog clutch is below a certain level the engagement will be without clonk noise. In this paper the designed state feedback Linear Quadratic Integral (LQI) control provides the synchronization torque request to the P1 motor, hence matching the speed of one side of dog clutch with the other under the disturbance from combustion torque of the engine.
The growing global adoption of electric vehicles (EVs) emphasizes the pressing need for a comprehensive understanding of thermal runaway in lithium-ion batteries. Prevention of the onset of thermal runaway and its subsequent propagation throughout the entire battery pack is one of the pressing challenges of lithium-ion batteries. In addition to generating excess heat, thermal runaway of batteries also releases hazardous flammable gases, posing risks of external combustion and fires. Most existing thermal runaway models in literature primarily focus on predicting heat release or the total amount of vent gas. In this study, we present a model capable of predicting both heat release and the transient composition of emitted gases, including CO, H2, CO2, and hydrocarbons, during thermal runaway events. We calibrated the model using experimental data obtained from an 18650 cell from the literature, ensuring the accuracy of reaction parameters.