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This study presents a reduced ionic chemical kinetics mechanism for predicting combustion phasing in methane-fueled homogeneous charge compression ignition (HCCI) engines. Starting from the detailed GRI-Mech 3.0 mechanism, a reduced scheme with 22 species and 48 reactions was developed. Ionic reactions were then added, forming a comprehensive mechanism with 27 species and 54 reactions. The mechanism was integrated into a multi-zone combustion model and validated against experimental data from a CFR engine under four operating conditions. Results show that the mechanism accurately predicts the start of combustion (SOC), with a maximum error below 0.09%. In-cylinder pressure and temperature profiles closely match experimental data. The model also captures the behavior of key radicals and ions, including H₃O⁺, OH⁻, and O₂⁻. Exhaust emissions such as CO and CO₂ are predicted with relative errors under 12%, while UHC predictions show moderate discrepancies. Notably, electrons are fully consumed during combustion, while some ions remain in the exhaust. The proposed mechanism offers a reliable and computationally efficient tool for combustion diagnostics and control, with potential applications in low-temperature and fuel-flexible engine technologies.

This study proposes an innovative Thermodynamic Activity Controlled Homogeneous Charge Compression Ignition (TAC-HCCI) strategy for diesel–natural gas dual-fuel engines, aiming to achieve high thermal efficiency while maintaining low emissions. By employing numerical simulation methods, the effects of the intake pressure, intake temperature, EGR rate, intake valve closing timing, diesel injection timing, diesel injection pressure, and diesel injection quantity on engine combustion, energy distribution, and emission characteristics were systematically investigated. Through a comprehensive analysis of optimized operating conditions, a high-efficiency and low-emission TAC-HCCI combustion technology for dual-fuel engines was developed. The core mechanism of TAC-HCCI combustion control was elucidated through an analysis of the equivalence ratio and temperature distribution of the in-cylinder mixture. The results indicate that under the constraints of PCP ≤ 30 ± 1 MPa and RI ≤ 5 ± 0.5 MW/m2, the TAC-HCCI technology achieves a gross indicated mean effective pressure (IMEPg) of 24.0 bar, a gross indicated thermal efficiency (ITEg) of up to 52.0%, and indicated specific NOx emissions (ISNOx) as low as 1.0 g/kW∙h. To achieve low combustion loss, reduced heat transfer loss, and high thermal efficiency, it is essential to ensure the complete combustion of the mixture while maintaining low combustion temperatures. Moreover, a reduced diesel injection quantity combined with a high injection pressure can effectively suppress NOx emissions.

The detailed mechanisms of n-heptane and n-butanol were reduced for the target condition of ignition delay time using the direct relationship diagram method based on error transfer, the direct relationship diagram method based on coupling error transfer and sensitivity analysis, and the total material sensitivity analysis method. The reduced n-heptane (132 species and 585 reactions) and n-butanol (82 species and 383 reactions) were used to verify the ignition delay time and concentrations of the major species, respectively. The results showed that the reduced mechanism has a good prediction ability for the ignition delay time. The predicted mole fraction results of the major species were in good agreement. These reduced mechanisms were combined to finally construct a reduced mechanism for the n-heptane/butanol fuel mixture, which included 166 species and 746 reactions. Finally, the reduced mechanism was used to simulate the HCCI combustion mode, and the results showed that the reduced mechanism can better predict the ignition and combustion timings of HCCI under different conditions and maintain the ignition and combustion characteristics of the detailed mechanism; this indicates that the mechanism model constructed in this study is reliable.

In the present study, performance of an HCCI engine powered with ethanol/toluene/n-heptane tri-fuel blend was optimized by using response surface method. The studied independent parameters were engine speed, lambda ratio, and fuel blends. The impact of these parameters on engine torque, COVimep, CA10, CA50, indicated thermal efficiency, IMEP along with emissions of NO X , CO, and HC comprehensively investigated. According to the results, the optimal HCCI engine operation condition was proposed as engine speed of 1343 rpm, lambda value of 2.29, and ethanol ratio of 22%. At this condition, the engine outputs, i.e., IMEP, COVimep, indicated thermal efficiency, CA10, and CA50, engine torque were estimated to be 4.21 bar, 4.28%, 0.37, 1.41 °CA, 4.62 °CA, and 8.2 Nm, respectively. The engine-out emissions, including HC, NO X , and CO emission, were predicted to be 243 ppm, 1.05 ppm, and 0.03%, respectively. The result indicates that using ethanol/toluene/n-heptane fuel mixture improved the HCCI combustion and NO X emission. The near-zero NO X emissions were recorded at all fuel mixture. However, enhancing ethanol ratio in the fuel blends showed an increase in CO and HC emissions. Overall, this study showed that response surface technique could be used as a promising method to model the HCCI engines.

The current study presents research investigations and developments related to the homogeneous charge compression ignition (HCCI) engine.  Research investigations and recent advances, including the role of various operating conditions on HCCI engine combustion phenomena, emissions, and performance, are discussed. There is growing research interest in investigating HCCI engines with diesel fuel to study combustion, emissions, and performance characteristics due to their association with low NO x emissions. In the published literature, research investigations are also conducted with different fuels ranging from biomass to diesel to gasoline in the HCCI engine showing its capability for utilizing various fuels in coming years. The challenges associated with HCCI combustion are reviewed, and the details of excessive carbon monoxide and unburnt hydrocarbon emissions are discussed. The major parameters affecting the hydrogen addition in HCCI diesel engines are also discussed. Overall, adding hydrogen to a diesel‐fueled HCCI engine improves combustion phasing and can potentially increase thermal efficiency while lowering emissions. In addition, the strength, weaknesses, opportunities, and threat analysis is provided and discussed thoroughly.

The combustion process in a Homogeneous compression charge ignition (HCCI) engine is complex and determined by the dynamics of chemical reactions, while the combustion timing remains challenging to control. To control this process and expand the operating range of HCCI, it is necessary to change the compression ratio, adjust the opening/closing time of the intake and exhaust valves, and manage the temperature (including internal or external exhaust gas recirculation). This paper studies the effects of oxygen concentration in the intake air and ambient temperature inside the combustion chamber on the HCCI combustion process in a Constant Volume Combustion Chamber (CVCC) using 10% Biodiesel (B10) and conventional Diesel fuel (B0). The experimental results show that ambient temperature and oxygen concentration have a significant influence on the combustion process. Higher temperature and oxygen concentration increase the fuel–air mixing rate, reduce the ignition delay, and improve the combustion efficiency. It makes the heat release rate faster and the rise in pressure stronger. These results are essential for optimizing the combustion chamber design and operating parameters to improve engine performance while minimizing emissions.Article HighlightsCVCC makes it easier to study the combustion process and assess how different factors affect it.The study shows that ambient temperature and oxygen levels have a significant impact on the combustion process.These findings are crucial for optimizing engines to improve performance while reducing emissions.

Probability Density Function (PDF) is often selected to couple chemistry with turbulence for complex reactive flows since complex reactions can be treated without modeling assumptions. This paper describes an investigation into the use of the particles approximation of this transport equation approach applied to Homogeneous Charge Compression Ignition (HCCI) combustion. The model used here is an IEM (Interaction by Exchange with the Mean) model to describe the micromixing. Therefore, the fluid within the combustion chamber is represented by a number of computational particles. Each particle evolves function of the rate of change due to the chemical reaction term and the mixing term. The chemical reaction term is calculated using a reduced mechanism of n-heptane oxidation with 25 species and 25 reactions developed previously. The parametric study with a variation of the number of particles from 50 up to 104 has been investigated for three initial distributions. The numerical experiments have shown that the hat distribution is not appropriate and the normal and lognormal distributions give the same trends. As expected when the number of particles increases for homogenous mixture (i.e. high turbulence intensity), the in-cylinder pressure evolution tends towards the homogeneous curve. For both homogeneous and inhomogeneous (i.e. low turbulence intensity) cases, we have found that 200 particles are sufficient to model correctly the system, with a CPU time of a few minutes when a restriction of initial distribution is adopted.

An optically accessible single-cylinder high speed direct-injection (HSDI) Diesel engine equipped with a Bosch common rail injection system was used to study low temperature Modulated Kinetics (MK) combustion with a retarded single main injection. High-speed liquid fuel Mie-scattering was employed to investigate the liquid distribution and evolution. By carefully setting up the optics, three-dimensional images of fuel spray were obtained from both the bottom of the piston and the side window. The NOx emissions were measured in the exhaust pipe. The influence of injection pressure and injection timing on liquid fuel evolution and combustion characteristics was studied under similar fuel quantities. Interesting spray development was seen from the side window images. Liquid impingement was found for all of the cases due to the small diameter of the piston bowl. The liquid fuel tip hits the bowl wall obliquely and spreads as a wall jet in the radial direction of the spray. Due to the bowl geometry, the fuel film moves back into the central part of the bowl, which enhances the air-fuel mixing process and prepares a more homogeneous air-fuel mixture. Stronger impingement was seen for high injection pressures. Injection timing had little effect on fuel impingement. No liquid fuel was seen before ignition, indicating premixed combustion for all the cases. High-speed combustion video was taken using the same frame rate. Ignition was seen to occur on or near the bowl wall in the vicinity of the spray tip, with the ignition delay being noticeably longer for lower injection pressure and later injection timing. The majority of the flame was confined to the bowl region throughout the combustion event. A more homogeneous and weaker flame was observed for higher injection pressures and later injection timing. The combustion structure also proves the mixing enhancement effect of the liquid fuel impingement. The results show that ultra-low sooting combustion is feasible in an HSDI diesel engine with a higher injection pressure, a higher EGR rate, or later injection timing, with little penalty on power output. It was also found that injection timing has more influence on HCCI-like combustion using a single main injection than the other two factors studied. Compared with the base cases, simultaneous reductions of soot and NOx were obtained by increasing EGR rate and retarding injection timing. By increasing injection pressure, NOx emissions were increased due to leaner and faster combustion with better air-fuel mixing. However, smoke emissions were significantly reduced with increased injection pressure.

Abstract Homogeneous charge compression ignition (HCCI) engines are drawing attention as the next-generation internal combustion engine, but have not been put to practical use because of several issues. One of the issues is that increasing the fuel charge causes rapid combustion in the combustion chamber, which results in knocking that limits its operation region. In this study, the focus was put on a method to increase the operation region of HCCI engines by mixing two fuels with different reactivities. First, dimethyl ether (DME), n-butane, or hydrogen was mixed with methane to investigate how the changes in mixing ratios affected the oxidation reaction of the pre-mixture based on numerical calculations with elementary reactions. From the calculation results, applicable types of double componential fuels for HCCI engines were considered. Based on the results of the consideration, DME or n-butane was mixed with methane to conduct combustion experiments and to clarify mixing conditions of the double componential fuels that realize high output and high thermal efficiency simultaneously.

Abstract A pre-chamber-type compression ignition natural gas engine was constructed and its performance and NO emissions were investigated. The pre- and main chambers made of ceramics were connected by a throat valve that opened during the compression stroke. An homogenous fuel air charge mixed with exhaust gas recirculation (EGR) gases was introduced into the main chamber, while a smaller amount of fuel was supplied into the pre-chamber during the intake stroke. The mixture in the pre-chamber was auto-ignited when the compressed hot gases in the main chamber were introduced into the pre-chamber through the throat valve during the compression stroke. The engine was operated without knock under various load conditions by adjusting the throat valve opening timing appropriately. The influences of the throat valve opening timing, compression ratio, and pre-chamber volume ratio on torque and NO emissions were investigated. Test results showed that: (a) at conditions when the thermal efficiencies were high, the patterns of the rate of heat release were similar to each other and independent of the compression ratio and pre-chamber volume ratio; (b) the optimum throat valve opening timing was strongly dependent on compression ratio and pre-chamber volume ratio; and (c) at conditions when the rate of heat release displayed two peaks - first low peak corresponding to the initial combustion in the pre-chamber and second high peak corresponding to combustion in the main chamber - low NO emissions below 20 ppm featuring homogeneous charge compression ignition (HCCI) combustion were achieved.