Browse Topic: Low temperature combustion (LTC)
Electrification of transport, together with the decarbonization of energy production are suggested by the European Union for the future quality of air. However, in the medium period, propulsion systems will continue to dominate urban mobility, making mandatory the retrofitting of thermal engines by applying combustion modes able to reduce NOx and PM emissions while maintaining engine performances. Low Temperature Combustion (LTC) is an attractive process to meet this target. This mode relies on premixed mixture and fuel lean in-cylinder charge whatever the fuel type: from conventional through alternative fuels with a minimum carbon footprint. This combustion mode has been subject of numerous modelling approaches in the engine research community. This study provides a theoretical comparative analysis between multi-zone (MZ) and Transported probability density function (TPDF) models applied to LTC combustion process. The generic thermo-kinetic balances for both approaches have been
With low-temperature combustion engine research reaching an applicable level, physics-based control-oriented models regain attention. For reactivity controlled combustion concepts, chemical kinetics-based multizone models have been proven to reproduce the governing physics for performance-oriented simulations. They offer accuracy levels similar to high-fidelity computational fluid dynamics (CFD) models but with a fraction of their computational effort. Nevertheless, state-of-the-art reactivity controlled compression ignition (RCCI) simulations with multizone model toolchains still face challenges related to predictivity and calculation speed. This study introduces a new multizone modelling framework that addresses these challenges. It includes a C++ code, deeply integrated with open-source, thermo-kinetic libraries, and coupled to an industry standard 1-D modelling framework. Incorporating a predictive turbulence mixing model, it aims to eliminate dependence on CFD-based initialisation
Premixed Charge Compression Ignition (PCCI) is a promising LTC strategy to reduce NOx and soot emissions without relying on after-treatment devices. One major drawback of PCCI is high HC and CO emissions resulting from fuel-wall impingement due to early injection of diesel. Narrow-angle direct injection (NADI) helps reduce the wall wetting of fuel. But it is effective only at lower loads. At mid and higher loads, it increases soot and CO emissions in small-bore engines due to the formation of fuel-rich pockets in the piston bowl region. This problem is addressed using a split injection strategy in the present work. A 3-D CFD model is developed and validated with experimental data at two load conditions. Simulations are performed using CONVERGE CFD software. Split injection strategies are explored using wide (148 deg) and narrow (88 deg) spray included angles. The investigations concluded that a main injection of 20 deg bTDC and 30 deg bTDC were optimal for wide and narrow spray
In the past years, stringent emission regulations for Internal Combustion (IC) engines produced a large amount of research aimed at the development of innovative combustion methodologies suitable to simultaneously reduce fuel consumption and engine-out emissions. Previous research demonstrates that the goal can be obtained through the so-called Low Temperature Combustions (LTC), which combine the benefits of compression-ignited engines, such as high compression ratio and unthrottled lean operation, with a properly premixed air-fuel mixture, usually obtained injecting gasoline-like fuels with high volatility and longer ignition delay. Gasoline Partially Premixed Combustion (PPC) is a promising LTC technique, mainly characterized by the high-pressure direct-injection of gasoline and the spontaneous ignition of the premixed air-fuel mixture through compression, which showed a good potential for the simultaneous reduction of fuel consumption and emissions in CI engines. Despite its
Low Temperature Combustion (LTC) is an emerging technology that offers an alternative to conventional spark and compression ignition. A highly discussed LTC mode is homogeneous charge compression ignition (HCCI), which consists in a combustion of a highly diluted well-mixed charge at the end of compression stroke, when the charge reaches the auto-ignition state. Since HCCI is an LTC mode, it can result in low NOX emissions with an indicated efficiency comparable to a diesel engine. Otherwise, there are some challenges to overcome such as achieving high loads without knocking and combustion timing control. Several methods to control the combustion had been investigated, between them, the injection of water may be useful to extend HCCI knock free operation and to enable combustion phasing control. This work investigated the influence of water injection in the intake of an ethanol HCCI cylinder from a converted diesel generator set. The EGR, used in HCCI, was obtained via total
Premixed charged compression ignition (PCCI) is a promising low temperature combustion strategy for achieving a simultaneous reduction of oxides of nitrogen (NOx) and soot emissions in diesel engines. However, early direct injection results in a significant penalty in fuel economy, high unburned hydrocarbon (HC), and carbon monoxide (CO) emissions, especially in small-bore diesel engines. In the present work, computational fluid dynamic (CFD) investigations are carried out in a small-bore diesel engine using a commercial CFD software, CONVERGE. The computational models are validated with experimental results at two different load conditions, 20% and 40% of rated load. The validated models are used to carry out parametric investigations on the effects of fuel injection parameters, namely the start of fuel injection timing, injection pressure, and spray cone angle on PCCI combustion. The fuel-air equivalence ratio, temperature, and emission contours are used to get more insight into the
Prior research studies have investigated a wide variety of gasoline compression ignition (GCI) injection strategies and the resulting fuel stratification levels to maintain control over the combustion phasing, duration, and heat release rate. Previous GCI research at the US Department of Energy’s Oak Ridge National Laboratory has shown that for a combustion mode with a low degree of fuel stratification, called “partial fuel stratification” (PFS), gasoline range fuels with anti-knock index values in the range of regular-grade gasoline (~87 anti-knock index or higher) provides very little controllability over the timing of combustion without significant boost pressures. On the contrary, heavy fuel stratification (HFS) provides control over combustion phasing but has challenges achieving low temperature combustion operation, which has the benefits of low NOX and soot emissions, because of the air handling burdens associated with the required high exhaust gas recirculation rates. This work
For controlling oxides of nitrogen (NOx) and particular matter (PM) emissions from diesel engines, various fuel and combustion mode modification strategies are investigated in the past. Low temperature combustion (LTC) is an alternative combustion strategy that reduces NOx and PM emissions through premixed lean combustion. Dual fuel reactivity-controlled compression ignition (RCCI) is a promising LTC strategy with better control over the start and end of combustion because of reactivity and equivalence ratio stratification. However, the unburned hydrocarbon (HC) and carbon monoxide (CO) emissions are significantly higher in RCCI, especially at part-load conditions. The present work intends to address this shortcoming by utilizing oxygenated alternative fuels. Considering the limited availability and higher cost, replacing conventional fuels completely with alternative fuels is not feasible. Based on this premise, oxygenated alternative fuel blends, viz. methanol and Karanja biodiesel
Extensive experimental investigations done over a decade in different engine types demonstrated the capability of achieving high efficiency along with low levels of oxides of nitrogen (NOx) and soot emissions with low temperature combustion (LTC) modes. However, the commercial application of LTC strategies requires several challenges to be addressed, including precise ignition timing control, reducing higher unburned hydrocarbon (UHC) and carbon monoxide (CO) emissions. The lower exhaust gas temperatures with LTC operation pose severe challenges for after-treatment control systems. Among the available LTC strategies, Reactivity Controlled Compression Ignition (RCCI) has emerged as the most promising strategy due to better ignition timing control with higher thermal efficiency. Nevertheless, the complexity of engine system hardware due to the dual fuel injection system and associated controls, high HC and CO emissions are the major limiting factors in RCCI. Homogeneous Charge with
The research on reducing emissions from automotive engines through modifications in the combustion mode and the fuel type is gaining momentum because of the increasing contribution to global warming by the transportation sector. The combustion and emission formation in the advanced low temperature combustion (LTC) engine strategies are susceptible to fuel molecular composition and properties. Ignition timing in LTC strategies is primarily controlled by fuel composition and associated chemical kinetics. Thus, tailoring of fuel properties is required to address the limitations of LTC in terms of lack of control on ignition timing and narrow engine operating load range. Utilizing fuel blends and additives such as nanoparticles is a promising approach to achieving targeted fuel property. An improved understanding of fundamental processes, including fuel evaporation, is required due to its role in fuel-air mixing and emission formation in LTC. In the present work, evaporation
Substantial fuel economy improvements for light-duty automotive engines demand novel combustion strategies. Low temperature combustion (LTC) demonstrates potential for significant fuel efficiency improvement; however, control complexity is an impediment for real-world transient operation. Spark-assisted compression ignition (SACI) is an LTC strategy that applies a deflagration flame to generate sufficient energy to trigger autoignition in the remaining charge. Operating a practical engine with SACI combustion is a key modeling and control challenge. Current models are not sufficient for control-oriented work such as calibration optimization, transient control strategy development, and real-time control. This work describes the process and results of developing a fast-running control-oriented model for the autoignition phase of SACI combustion. A data-driven model is selected, specifically artificial neural networks (ANNs). The models are trained to an experimentally-validated one
The aim of this paper is to computationally investigate the combustion behavior and energy recovery processes of a six-stroke gasoline compression ignition (6S-GCI) engine that employs a continuously variable valve duration (CVVD) technique, under highly diluted, low-temperature combustion (LTC) conditions. The effects of variation of parameters concerning injection spray targeting (number of fuel injector holes. injector nozzle size and spray included angle) and combustion chamber geometry (piston bowl design) are analyzed using an in-house 3D CFD code coupled with high-fidelity physical sub-models with the Chemkin library in conjunction with a skeletal chemical kinetics mechanism for a 14-component gasoline surrogate fuel. The foundation of this study stems from the authors previous works, regarding the effects of the change in various operating parameters on the overall performance of 6S-GCI engine, which show that both kinetically-controlled mode of combustion (KCM) and mixing
With the increasing demand of emission reductions from the automotive industry, advanced after-treatment strategies have been investigated to overcome the challenges associated with meeting increasingly stringent emission regulations. Ongoing investigations on low temperature combustion (LTC) strategies are being researched to meet future emission regulations, however, the lowered exhaust temperature presents an even greater issue for exhaust after-treatment due to the change in combustion modes. Catalyst temperature is critical for the catalytic ability to maintain effective conversion efficiency of regulated emissions. The use of periodic flow reversal has shown benefits of maintaining catalyst temperature by alternating the exhaust flow direction through the catalytic converter, reducing the catalyst sensitivity to inlet gas temperature fluctuations. Cyclically alternating the exhaust flow direction can produce a thermal wave, elevating the central catalyst temperature above the
Environmental pollution as a result of improper disposal of agricultural and food industry waste has been a concern lately. In the present study, an attempt has been made to produce energy from these wastes. Biodiesel produced from residual cooking oil (RCOB) and hexanol produced from agricultural waste have been investigated as alternatives to petroleum-based fossil fuels in a dual-fuel low-temperature combustion engine. Hexanol was injected in the inlet port at 3 bar injection pressure whereas RCOB was injected directly inside the combustion chamber using a common rail direct injection system. The proportion of Hexanol to RCOB was varied from 40% to 60% at rated load. The operating parameters such as intake air temperature, exhaust gas recirculation (EGR) quantity along with multiple injection timing, duration, quantity, and pressure were optimized for lower oxides of nitrogen (NOx) and smoke emissions. Intake air temperature of 40 °C, EGR rate of 30 %, and direct injection timings
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