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Energy management strategies (EMSs) are a core technology in hybrid electric vehicles (HEVs) and have a significant impact on their fuel economy. Optimal solutions for EMSs in the literature usually focus on improving fuel efficiency by operating the engine within a high efficiency range, without considering the drivability, which is affected by noise–vibration–harshness (NVH) constraints at low vehicle speeds. In this paper, a dual-mode combustion engine was implemented in a plug-in series hybrid electric vehiclethat could operate efficiently either at low loads in homogeneous charge compression ignition (HCCI) mode or at high loads in spark ignition (SI) mode. An equivalent consumption minimization strategy (ECMS) combined with a dual-loop particle swarm optimization (PSO) algorithm was designed to solve the optimal control problem. A MATLAB/Simulink simulation was performed using a well-calibrated model of the target HEV to validate the proposed method, and the results showed that it can achieve a reduction in fuel consumption of around 1.3% to 9.9%, depending on the driving cycle. In addition, the operating power of the battery can be significantly reduced, which benefits the health of the battery. Furthermore, the proposed ECMS-PSO is computationally efficient, which guarantees fast offline optimization and enables real-time applications. [ABSTRACT FROM AUTHOR]

Interest in hydrogen-powered engines is growing due to their potential to reduce greenhouse gas emissions and decrease reliance on fossil fuels. This research examines how the start of combustion (SOC) impacts the performance of homogeneous charge compression ignition (HCCI) engines using hydrogen exclusively. Using numerical simulations with a 0D multi-zone HCCI model, the study investigates parameters such as compression ratio (CR), equivalence ratio (ER), and intake charge temperature (ICT) to assess their influence on engine performance. The results uncover hydrogen’s unique combustion behaviour, characterised by its physiochemical properties and low-temperature combustion. The study identifies an optimal ER range of 0.1 to 0.3, with various ICTs and it is playing a pivotal role in promoting auto-ignition and accelerating combustion. However, an ER of 0.4 and ICT of 393 K produces relatively higher indicated thermal efficiency, which is affected by knocking due to a higher rate of pressure rise, constraining the ER range. Additionally, the research explores the potential of charge dilution to expand the ER range in HCCI mode. These insights provide valuable guidance for enhancing the operation of hydrogen-fuelled HCCI engines, facilitating the transition to cleaner and more efficient propulsion systems in transportation. [ABSTRACT FROM AUTHOR]

By dividing combustion chamber, the homogeneous charge compression ignition (HCCI) combustion can be achieved the multi-stage. The combustion system has two parts of combustion chamber, one is small inside piston and the other is large. At first, ignition takes place in the small chamber inside piston, and then the burned gas ejected into the large chamber to ignite the mixture in the large chamber. This combustion system is promising to reduce maximum pressure rise rate so can be achieved high load operation without knocking. The 3D-CFD results have shown that over 50% (maximum 51.4%) of indicated thermal efficiency at IMEP 1.1 MPa operation with exhaust gas recirculation (EGR) and fueled with iso-octane and iso-octane mixed with ethanol 10vol.% and 15vol.% (E10 and E15, respectively). [ABSTRACT FROM AUTHOR]

Research on engines using different combustion principles has been spurred up by widespread worries about dangerous pollutants, stringent emission restrictions, and global warming. Low Temperature Combustion (LTC) is a cutting-edge idea for internal combustion engines that will be able to replace the standard modes of combustion and have the benefit of using both conventional and renewable fuels. In this sense, LTC has garnered interest on a worldwide scale recently, particularly the Homogeneous Charge Compression Ignition (HCCI) mode. The absence of flame propagation or diffusive flame distinguishes this combustion mechanism from spark ignition and compression ignition. On the contrary, chemical kinetics controls HCCI combustion. When the mixture approaches chemical activation in HCCI engines, which employ much diluted homogenous charge, auto ignition occurs simultaneously in several locations. In comparison to diesel engines, HCCI technology enables high efficiency operating with little nitrogen oxide, soot, and particulate matter emissions. The primary obstacles to be addressed are, however, the regulation of ignition timing, the impossibility of the high load operation, as well as increasing emissions of carbon monoxide and unburned hydrocarbons. The past and current work across the globe has revealed that engine working on HCCI module can be fuelled with different fuels with little emissions and high efficiencies. All the past work has been mentioned and explained in this current work. [ABSTRACT FROM AUTHOR]

Introduction of internal EGR (Exhaust Gas Recirculation) is effective for improving the efficiency of ICE (Internal Combustion Engine), though the combustion stability usually limits its maximum amount. In this study, we modelled the dynamics of the cycle-to-cycle variation of the HCCI(Homogeneous Charge Compression Ignition) combustion, designed a controller that actuates fuel injections based on the dynamics, and evaluated it on real engines. The experiment of the controller showed the improvement of the fuel efficiency and possibility of extending the limit of the Internal EGR amount. [ABSTRACT FROM AUTHOR]

Energy management strategies (EMSs) are a core technology in hybrid electric vehicles (HEVs) and have a significant impact on their fuel economy. Optimal solutions for EMSs in the literature usually focus on improving fuel efficiency by operating the engine within a high efficiency range, without considering the drivability, which is affected by noise–vibration–harshness (NVH) constraints at low vehicle speeds. In this paper, a dual-mode combustion engine was implemented in a plug-in series hybrid electric vehiclethat could operate efficiently either at low loads in homogeneous charge compression ignition (HCCI) mode or at high loads in spark ignition (SI) mode. An equivalent consumption minimization strategy (ECMS) combined with a dual-loop particle swarm optimization (PSO) algorithm was designed to solve the optimal control problem. A MATLAB/Simulink simulation was performed using a well-calibrated model of the target HEV to validate the proposed method, and the results showed that it can achieve a reduction in fuel consumption of around 1.3% to 9.9%, depending on the driving cycle. In addition, the operating power of the battery can be significantly reduced, which benefits the health of the battery. Furthermore, the proposed ECMS-PSO is computationally efficient, which guarantees fast offline optimization and enables real-time applications.

This paper investigated the effects of exhaust gas recirculation (EGR) on homogeneous charge compression ignition (HCCI) combustion in internal combustion engines. The exhaust valve closing (EVC) timings were scanned to obtain a set of baseline operating points for HCCI, and the coupling control of the internal and external EGR was explored. The results indicate that external EGR delays HCCI ignition timing and slows down the combustion speed. As the internal EGR rate increases, the maximum external EGR ratio that can be tolerated decreases. For HCCI detonation operating points with low internal EGR rates, the addition of up to 10% of external EGR can control the pressure rise rate peak to less than 10 bar/°CA, resulting in reduced fuel consumption and increased indicated mean effective pressure (IMEP). However, for HCCI operating points with high internal EGR rates, the effect of external EGR is mainly observed in the control of the pressure rise rate, with limited increase in IMEP. Additionally, an increasing external EGR rate leads to a significant decrease in nitrogen oxide (NOx) emissions, while carbon monoxide (CO) and hydrocarbon (HC) emissions slightly increase before engine misfire occurs. These findings suggest that the coupling control of internal and external EGR should be explored further, particularly in relation to reducing the negative valve overlap (NVO) angle and improving combustion efficiency. [ABSTRACT FROM AUTHOR]

Homogeneous Charge Compression Ignition (HCCI) engines promise better efficiency and cleaner emissions than conventional piston engines, but can be challenging to control. Rapid compression machines (RCM) provide a simplified configuration for investigating HCCI combustion behavior, which is necessary for effective control of engine ignition timing and peak pressures. In this study, we assess the utility of large eddy simulations (LES) for predicting HCCI combustion in a 3-D configuration. To this end, LES with finite-rate chemistry employing a 99-species iso-octane/air mechanism of two RCM operating conditions are performed. The RCM configuration under consideration was designed by Strozzi et al. (Combust. Flame, 2019) with a flat piston to introduce large amounts of thermal stratification representative of realistic HCCI engine conditions, through the generation of corner vortices. It is shown that the simulation provides reasonable agreement with temperature fluctuations (7% difference), as well as ignition delay in the short ignition case (1 ms difference), while the long ignition case (35 ms difference) highlights more substantial deficiencies that are still within the expected uncertainty from the employed chemical mechanism. Flame propagation modes predicted by LES agree with experimental observations: spontaneous ignition is seen in the short ignition case, while deflagration is more prominent in the long ignition case. Analysis of global and local quantities classify the short ignition case in a mixed ignition regime, and the long ignition case in the mild ignition regime. These results demonstrate the utility of FRC-LES for investigations of multimode combustion regimes of HCCI combustion in a 3-D configuration. [ABSTRACT FROM AUTHOR]

Diesel engines are commonly employed for transportation and power generation. Injection of diesel into the cylinder plays a crucial role towards cycle efficiency and emission regulations. The literature overview of several parameters, such as swirl ratio, injection timing, exhaust gas recirculation, fuel temperature and combustion chamber geometry, is presented in this review work. It is suggested that Computational Fluid Dynamics (CFD) simulations inside the cylinder are useful for predicting the flow field, combustion and pollutant formation. Future directions are indicated for further research on direct injection diesel engines. [ABSTRACT FROM AUTHOR]

To obtain a smaller-scale ammonia-hydrogen hybrid mechanism with better predictive performance suitable for HCCI engine combustion, the stagni mechanism, which is closer to the combustion temperature, pressure and equivalence ratio conditions of HCCI engine, is selected as the original mechanism based on six ammonia-hydrogen detailed mechanisms, and the new detailed mechanism is obtained by adjusting the reaction rate constants related to HCCI combustion. Using three reduced methods, Directed Relation Graph with Error Propagation (DRGEP), Directed Relation Graph with Path Flux Analysis (DRGPFA) and Full Species Sensitivity Analysis (FSSA). Based on the allowable residual of 5%, the detailed mechanism of ammonia-hydrogen combustion is reduced. Based on sensitivity analysis to select key primitive responses, the pre-exponential factors of the reduced mechanism were designed by response surface method, and a series of optimization parameters were obtained. The optimization parameters are used to optimize the pre-exponential factor and verify the optimization mechanism. The results show that under the combination of R45=3.2×1011, R46=2.53862×1019, R103=338; R6=5.12×1022, R28=249 and R79=1.2×1012, the response value of predicting ignition delay time and laminar flame speed is the largest, and the error between the optimization mechanism and the detailed mechanism is the smallest, which proves the accuracy of the optimization parameters. The optimized mechanism has good prediction performance under HCCI conditions and can be used as an ammonia-hydrogen mixing mechanism suitable for HCCI engines.

Homogeneous Charge Compression Ignition (HCCI) is a low temperature combustion technique with a high potential for reducing emissions while simultaneously improving fuel consumption. However, the high sensitivity to changing boundary conditions and low combustion stability at the edges of the operating range has lead to implementation challenges. Additionally, cyclic coupling through internal exhaust gas recirculation causes cyclic variations of the process, resulting in incomplete combustion, or even misfiring. Thus, consecutive cycles must be decoupled to increase the process stability. To achieve an accurate description of the coupling effects on a cycle-to-cycle and an inner-cyclic timescale, a novel measurement methodology is presented to generate data with a high variance. For this purpose, an active process excitation is performed to capture all relevant interactions between operating and feedback variables to enable modeling of the coupling effects on both timescales. To demonstrate the potential of the methodology, the generated data is used to design multiple input, multiple output (MIMO) models for both cyclic and inner-cyclic timescales. Artificial neural networks are then utilized to address the highly nonlinear process by taking advantage of the large amount of training data. Inverse process models are then used to implement a pure cycle-to-cycle and a multiscale MIMO closed-loop controller. Compared to state-of-the-art rule-based control approaches, the process stability and its thermodynamic efficiency are significantly improved. For the multiscale MIMO controller, a reduction of the standard deviation of the indicated mean effective pressure and the combustion phasing of more than 65% is achieved. In particular, the additional inner-cyclic feedback loop achieves a remarkable reduction of the standard deviation of approximately 35% and a 1.2% higher indicated efficiency compared to the cycle-to-cycle MIMO controller. The dynamic measurement with active in-cycle process excitation has proven to be an enabler for data-driven MIMO control of HCCI on multiple timescales. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition (HCCI) promises low NO x emissions and high efficiency due to fast combustion at low temperatures. However, the control of combustion timing represents a serious challenge due to the lack of dedicated ignition control parameters. This challenge is addressed in this work by means of a hot surface ignition (HSI) system, whose core element consists of a shielded, electrically heated ceramic glow plug. In this approach, termed as hot surface assisted compression ignition (HSACI), a small portion of mixture is thought to ignite in the vicinity of the shielded glow plug and to subsequently propagate to the main combustion chamber in order to initiate bulk-gas auto-ignition. Adjusting the hot surface temperature enables to either advance or retard the onset of combustion and thus, allows to control combustion timing. This paper presents experimental results of initial engine trials, using the HSACI concept in a naturally aspirated single cylinder natural gas engine. Measurements were conducted at a constant engine speed of 1400 l/min and include intake air temperatures in the range of 150–175°C and relative air-fuel ratios (λ) from 2.0 to 2.8. Results show that the HSI system enables combustion under conditions, which do not allow for pure HCCI operation. Moreover, the combustion timing can be actively controlled within certain limits by changing the HSI temperature. Increasing cycle-to-cycle variations limit stable operation at lower temperatures, while a transition to pure HCCI is found at intake temperatures beyond 170°C. The applicable λ range is limited by knocking or uncontrolled combustion toward the rich side and instable operation toward the lean side. Loss analysis points out that wall heat flow and imperfect combustion represent the dominant loss mechanisms. Heat release analysis reveals two pronounced phases, indicating initial flame propagation and subsequent auto-ignition similar to spark assisted compression ignition (SACI). [ABSTRACT FROM AUTHOR]

The internal combustion engine faces increasing societal and governmental pressure to improve both efficiency and engine out emissions. Currently, research has moved from traditional combustion methods to new highly efficient combustion strategies such as Homogeneous Charge Compression Ignition (HCCI). However, predicting the exact value of engine out emissions using conventional physics-based or data-driven models is still a challenge for engine researchers due to the complexity the of combustion and emission formation. Research has focused on using Artificial Neural Networks (ANN) for this problem but ANN's require large training datasets for acceptable accuracy. This work addresses this problem by presenting the development of a simple model for predicting the steady-state emissions of a single cylinder HCCI engine which is created using an metaheuristic optimization based Support Vector Machine (SVM). The selection of input variables to the SVM model is explored using five different feature sets, considering up to seven engine inputs. The best results are achieved with a model combining linear and squared inputs as well as cross correlations and their squares totaling 26 features. In this case the model fit represented by R 2 values were between 0.72 and 0.95. The best model fits were achieved for CO and CO2, while HC and NOx models have reduced model performance. Linear and non-linear SVM models were then compared to an ANN model. This comparison showed that SVM based models were more robust to changes in feature selection and better able to avoid local minimums compared to the ANN models leading to a more consistent model prediction when limited training data is available. The proposed machine learning based HCCI emission models and the feature selection approach provide insight into optimizing the model accuracy while minimizing the computational costs. [ABSTRACT FROM AUTHOR]

Wet ethanol is a renewable fuel that has great potential to reduce the energy cost of ethanol production and improve the life-cycle carbon footprint of ethanol. The use of wet ethanol in homogeneous charge compression ignition (HCCI) mode can achieve high efficiency with low emission levels. In this context, this study investigates the effects of water-in-ethanol concentration on the performance, emissions, and combustion characteristics of an HCCI engine using water injection and recirculation of all exhaust gasses from a diesel cylinder. Water injection was used to solve the problem that there is no direct method to adjust HCCI combustion. Results showed that water–ethanol blends with higher water content had lower heat release rates and combustion temperatures, which increased the combustion duration. The indicated efficiency deteriorated for ethanol–water blends with high water concentrations. However, the highest indicated efficiency was 39.3% for the blend with 20% water by vol. at 6.0 bar. CO and organic gas emissions tended to increase with late combustion and for blends with higher water content, reaching values of 78.0 and 68.2 g/kWh at 4.0 bar, respectively. On the other hand, the NOX emissions were low, reaching a maximum value of 0.93 g/kWh in the HCCI combustion.

A numerical model of the micro-free-piston engine was developed and its correctness was verified by the comparison between the simulation and referential experiment results under the same work conditions. Based on this numerical model, the effects of the water vapor blending ratio (α) on combustion thermal performance and emission characteristics of hydrogen (H2) homogeneous charge compressing ignition (HCCI) were investigated numerically. The water vapor impact on combustion temperature was analyzed as well. The simulation results reveal that when the initial equivalent ratio is 0.5, blending H2 with water vapor can delay the ignition time and prolong the whole process. At the same time, the addition of water vapor to H2 decreases the peak combustion temperature and pressure, which will alleviate the detonation phenomenon of the combustion chamber. Moreover, the power output capacity and NOx emissions decrease with the increase in α. When α increases to 0.8, the mixture gas cannot be compressed to ignite. Finally, the dilution effect, thermal effect, and chemical effect of water vapor all have the potential to lower the combustion temperature and the dilution effect plays the leading role. [ABSTRACT FROM AUTHOR]

Partial fuel stratification (PFS) is a low temperature combustion strategy that can alleviate high heat release rates of traditional low temperature combustion strategies by introducing compositional stratification in the combustion chamber using a split fuel injection strategy. In this study, a three-dimensional computational fluid dynamics (CFD) model with large eddy simulations and reduced detailed chemistry was used to model partial fuel stratification at three different stratified conditions. The double direct injection strategy injects 80% of the total fuel mass at −300 CAD aTDC and the remaining 20% of the fuel mass is injected at three different timings of −160, −50, −35 CAD to create low, medium, and high levels of compositional stratification, respectively. The PFS simulations were validated using experiments performed at Sandia National Laboratories on a single-cylinder research engine that operates on RD5-87, a research-grade E10 gasoline. The objective of this study is to compare the performance of three different reduced chemical kinetic mechanisms, namely SKM1, SKM2, and SKM3, at the three compositional stratification levels and identify the most suitable mechanism to reproduce the experimental data. Zero-dimensional chemical kinetic simulations were also performed to further understand differences in performance of the three reduced chemical kinetic mechanisms to explain variations in CFD derived heat release profiles. The modeling results indicate that SKM3 is the most suitable mechanism for partial fuel stratification modeling of research-grade gasoline. The results also show that the autoignition event progresses from the richer to the leaner compositional regions in the combustion chamber. Notably, the leaner regions that have less mass per unit volume, can contribute disproportionately more toward heat release as there are more cells at leaner equivalence ratio ranges. Overall, this study illuminates the underlying compositional stratification phenomena that control the heat release process in PFS combustion. [ABSTRACT FROM AUTHOR]

In the research carried out for this paper, an injection strategy for predictably PCCI combustion with Alternative fuel of GTL, a series of experiments using a single-cylinder diesel engine and a spray observation vessel. The Injection system was revised by several injection timing, rate of injection quantities, and second injection ratio to optimize for spray-to-spray collision and spatial and temporal distribution of the mixture. The results show that switching injection pattern improve IMEP, and the spray-to-spray collide two-stage injection, reduces NO without increasing CO and THC emissions. [ABSTRACT FROM AUTHOR]

An automatic adjustment method of the model-based controller of an HCCI engine was designed in this study. As modeling errors are inevitable, feedback control is usually introduced to reduce the effect of the modeling errors. However, especially under transient conditions, the control performance may deteriorate, because this is a control with the information of the previous cycle. The transient control performance is thought to be improved by taking modeling errors into consideration. Therefore, an algorithm to adjust the feedback input based on the prediction of the modeling error was developed. The modeling error was learned and predicted by ReOS-ELM (Regularized Online Sequential Extreme Learning Machine), which is a method of online machine learning with low computational load. The modeling error learning was conducted every engine cycle. The feedback input was adjusted so that the output prediction by the engine model including its modeling error prediction coincided with the output reference. The reference tracking performance was improved by the proposed method.

Homogeneous charge compression ignition engines are engines with low temperature combustion tendency and high thermal efficiency. The operating range of these engines, where there is no direct control over combustion, is limited because of knock and misfire problems. At this point, it is aimed to eliminate the knocking problem especially at high loads with the mixture composition taken into the cylinder and different operating parameters. HCCI combustion is highly affected by engine operating parameters. In this study, a single-cylinder four-stroke spark-ignition engine was converted to a homogeneous charge compression ignition engine. The test engine was operated with hexane and n-heptane fuel mixtures at 1400 rpm and between 1.9 and 2.74 air excess ratio in full load HCCI combustion mode. The effects of hexane fuel on cylinder pressure, heat release rate, in-cylinder temperature, combustion duration, start of combustion, cyclic variations, knock density, indicated mean effective pressure (imep), thermal efficiency and emissions (HC and CO) were investigated experimentally. In the experiments carried out at constant intake air inlet temperature, it was observed that the cylinder pressure and heat release rate decreased with increasing air excess ratio. As a result, HCCI combustion was found to be highly affected by air excess ratio and fuel composition. It has also been found that the range of operation can be extended in the knock boundary zone in HCCI combustion.

Homogeneous charge compression ignition (HCCI) combustion is promising a new combustion system reducing NOx and PM simultaneously without any penalty of fuel consumption. However, the operational range of the HCCI combustion system is limited because of some issues such as poor control of ignition timing and the excessive rate of pressure rise. In this study, a new combustion system based on the HCCI combustion process has been proposed. The combustion system has a divided combustion chamber of two parts, one is small and the other is large. On the combustion system, at first, ignition takes place in the small chamber, and then the burned gas ejected into the large chamber to ignite the mixture in the large chamber. In the combustion system, the combustion process in the large chamber is aimed to go on same manner of the HCCI combustion process. This paper presents the effects of compression ratio, supplying same fuel to the large chamber and the small chamber and EGR on engine performance, combustion characteristics and exhaust emissions. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition (HCCI) has attracted lots of attention due to the high thermal efficiency, lower NOx, and Soot exhaust emissions. Heat transfer from the gases to the combustion chamber walls has an effective impact on the combustion process and the formation of engine-out emissions in the HCCI engine. In this study for the first time, a zerodimensional single-zone model coupled with detailed chemical kinetics was used to evaluate the semi-empirical heat transfer models of Annand, Woschni, Hohenberg along with Assanis and Hensel to calculate heat flux in an HCCI engine fueled with natural gas. For this purpose, the 3D-CFD model coupled with detailed chemical kinetics was firstly validated by using experimental data, and then the 3D derived model was used as a base model for evaluating a zero-dimensional model. Furthermore, the response surface model (RSM) was employed for investigating the effect of input parameters of the engine including intake pressure (1, 1.25, and 1.5bar), equivalence ratio (0.3, 0.5, and 0.7), and engine speed (800, 1100, and 1400rpm) on the output parameters i.e., in-cylinder pressure and heat flux. In most cases were assessed, the zero-dimensional simulation results indicated that the Annand technique provided the best model for heat flux simulation. Besides, the model of Hohenberg overpredicts the heat flux in comparison with the calculated values derived from the 3D model, while Assanis and Hensel models underpredict the heat flux compared with the evaluated value of the 3D model. Furthermore, Woschni’s model cannot be used to model the heat flux in the HCCI engine. [ABSTRACT FROM AUTHOR]

With high oxygen content and cetane number, PODE3 is a favorable renewable fuel for engines. PODE3/diesel/gasoline blends in a HCCI engine are numerically studied for the first time. The effects of fuel blend ratio and equivalence ratio (ER) on auto-ignition are investigated. A highly compact and robust chemical mechanism has been implemented. Crank angle at which 50 percent of heat is released (CA50) displays higher sensitivity towards blend ratio in leaner mixtures with 50% PODE3 displaying a change of 12.31 CAD at 0.34 ER and only 6.19 CAD at 0.5 ER when made in comparison to their respective CA50 at 100% PODE3. Furthermore, indicated thermal efficiency (ITE) is observed to be better with higher ER with 100% PODE3 having a 23.3% increase in ITE at 0.5 ER than at 0.34 ER, and is generally higher with increased PODE3. Neat PODE3 displays lowest CO and highest CO2 for all cases, manifesting high oxidation reactivity. Additionally, acetylene levels are substantially lower for combustions at 0.5 ER as compared to 0.34 ER. Lastly, PODE3 yields only 2.04 × 10−10g/cycle and 5.67 × 10−11g/cycle of C2H2 at 0.34 ER and 0.5 ER respectively. With nearly no soot precursors, PODE3 demonstrates high potential in encouraging clean combustion.

Low Temperature Combustion (LTC) strategies are most promising to simultaneously reduce oxides of nitrogen (NOx) and soot emissions from diesel engines along with offering higher thermal efficiency. Commercial wide spread implementation of diesel LTC strategies requires several challenges to be addressed, including lack of precise ignition timing control, widening the narrow operating load ranges and reducing high unburned fuel emissions. These challenges can be addressed through modifications in the engine or fuel design or both. The timing and rate of combustion in several LTC strategies are controlled primarily by the chemical kinetics of the fuel. Since, diesel fuel reactivity and volatility are tailor-made to perform well under conventional diesel combustion conditions, its application in LTC poses several problems, as highlighted in this paper. Hence, it is important to identify suitable alternative fuels for the different diesel LTC strategies. The published literature on LTC over the past 25 years is critically analyzed to discuss the evolution of the different diesel LTC strategies, their operability limits, the challenges and the controlling parameters for each strategy. This is followed by in-depth analysis of the role of the fuel and the fuel requirements for each strategy. Further, the importance of adopting a hybrid surrogate modeling approach to enable numerical simulation of diesel LTC is highlighted. A novel attempt of relating various diesel low temperature combustion (LTC) strategies based on the approach followed to achieve positive ignition dwell through different injection strategies, utilizing high exhaust gas recirculation (EGR), and dual fuels is presented. The need for replacing diesel with alternative liquid fuels in LTC strategies is presented by highlighting the fundamental problems associated with diesel fuel characteristics. The review concludes by suggesting potential alternative fuels for various diesel LTC strategies and provides directions for future work to address the challenges facing compression ignition LTC operation. [ABSTRACT FROM AUTHOR]

In-cylinder pressure oscillations in internal combustion engines have been associated with increased heat losses and damages to the engine components. The links between the acoustic waves and the increased heat transfer (and potentially ensuing engine damages) have not yet been well understood. In this study, a high-fidelity large eddy simulation model incorporating an auto-ignition model is used to simulate the combustion process and the associated pressure oscillation at various engine operating conditions. The study serves to develop a better understanding of the acoustic waves in a combustion chamber and their effect on wall heat transfer. First, a simplified model of the pressure oscillations is proposed and shown to accurately characterize the pressure in the combustion chamber. Second, the simplified pressure model and acoustic theory are leveraged to develop a model of the in-cylinder gas velocities. Finally, a heat transfer model is presented that takes into consideration the pressure/velocity oscillations and the inherent acoustic properties of the trapped gas. The increase in heat transfer is shown to primarily stem from an increased heat transfer coefficient due to the velocity oscillations of the trapped gas. The results are consistent with previously observed experimental measurements of the heat flux in the presence of pressure oscillations. [ABSTRACT FROM AUTHOR]

The very intensive calculations necessary to define a performance map requiring evaluation of over a hundred individual operating points can be efficiently conducted with accelerated multizone for engine cycle simulation, leading to a definition of regions of acceptable and optimum homogeneous charge compression ignition operation. Accelerated multizone for engine cycle simulation has the virtue of enabling accurate evaluation of many operating conditions based on thermal stratification data from a single fluid mechanics run at motored conditions. This is possible because thermal stratification is more sensitive to engine geometry than to operating conditions. In this article, accuracy of accelerated multizone for engine cycle simulation is demonstrated by comparison with experimental data for iso-octane homogeneous charge compression ignition operation over a broad range of lean equivalence ratios (0.14–0.28). The validated accelerated multizone for engine cycle simulation model is then applied to generating a performance map for an engine controlled by appropriately adjusting equivalence ratio and internal exhaust gas recirculation. Regions of acceptable and optimum combustion are identified. It is finally demonstrated that while indicated mean effective pressure remains low for optimum homogeneous charge compression ignition operation (1–4 bar), this is sufficient for a large fraction of typical driving in light-duty vehicles. Much driving including idle can therefore be done in homogeneous charge compression ignition mode at high efficiency and low (essentially zero) NO x and particulate matter emissions. [ABSTRACT FROM AUTHOR]

Prior experiments reported by the authors have proven the hypothesis that achieving a dynamic temperature swing on the combustion chamber surface will lead to improved thermal and combustion efficiencies of the homogeneous charge compression ignition engine. A thin layer of yttria-stabilized zirconia, roughly 150 mm, was plasma sprayed on the piston top. It led to markedly advanced ignition and heat release in the gasoline homogeneous charge compression ignition engine, accompanied with reduced unburnt hydrocarbon and carbon monoxide emissions, improved combustion efficiency, and a higher thermal efficiency. A related computational study highlighted the critical role of coating thermal conductivity in achieving a desired dynamic response; hence, the second phase of experimental investigations focused on introducing structured porosity in the yttria-stabilized zirconia coating, as a means of reducing effective conductivity. Indeed, additional incremental improvements were observed, as well as limitations related to adverse effects of the surface roughness and the fuel interactions with the surface roughness and open pores. Erosion can also be a problem in a direct injection engine. Therefore, the third round of investigations focused on a material with a natively low conductivity (low-k), sprayed on the top of an Al piston in a relatively dense form, and in a way that yields a smooth surface. The objective was to capitalize on the low conductivity, while avoiding the pitfalls accompanying high-porosity formulations. The heat-storage capacity was limited by keeping the thickness relatively low. The results verify the paramount importance of thermal conductivity in the context of high 'temperature swing" behavior and indicate a potential to improve the homogeneous charge compression ignition engine's combustion efficiency roughly 1.5%, with the overall indicated efficiency improvement on the order of 5%, on a relative basis. In addition, the low-k oxide thermal barrier applied to the piston extended significantly the low-load homogeneous charge compression ignition operability limit. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition has proven to be both highly efficient and to operate with ultra-low NOx raw emissions. However, homogeneous charge compression ignition combustion is a dynamic process due to strong cycle-to-cycle coupling effects caused mainly by the residual gas. Compared to conventional spark-ignited and diesel engines, the lack of direct mixture composition and ignition control increases the challenge of combustion instabilities, especially at boundary conditions. To stabilize the combustion process, real-time in-cylinder combustion diagnostics and control are often used. In this study, for the first time, ion current detection technology and direct water injection are combined for homogeneous charge compression ignition combustion control. By analyzing the return map of the crank angle at 50% cumulative heat release under unstable conditions, it was identified that a misfire or incomplete combustion is usually followed by knocking-like early combustion with high cylinder pressure gradients. Through the correlation analysis between ion current and combustion, a cycle-to-cycle closed-loop control strategy was developed and implemented on a rapid control prototyping engine control unit. Real-time calculated ion current parameters were used to predict the 50% cumulative heat release position of the next cycle and prevent early combustion by direct water injection. The calculation results and controller performance were validated on a single-cylinder research engine. With the controller activated, the standard deviation of 50% cumulative heat release and dynamic programming to the max could be reduced by 19% and 11%, respectively. The coefficient of variation of indicated mean effective pressure was reduced by 12%. A slight increase in indicated mean effective pressure after activating the controller also shows the potential for efficiency improvement. Moreover, not only early combustion is controlled, but also late combustion is significantly reduced. [ABSTRACT FROM AUTHOR]

A 74-species reduced mechanism and a 94-species skeletal mechanism for bio-butanol oxidation were obtained from a 234-species detailed mechanism using an integrated reduction method involving directed relation graph (DRG), DRG-related and computational singular perturbation (CSP) + quasi-steady-state approximation (QSSA) methods. Firstly, the skeletal mechanism with 94 species and 497 reactions was derived by comparing the DRG and DRG-related methods. Then, 112 unimportant reactions were identified and eliminated through the CSP importance index method, and the final skeletal mechanism with 94 species and 385 reactions was generated. Finally, a reduced mechanism with 74 species and 70 step reactions was derived by using the CSP + QSSA method to identify and eliminate 20 QSS species. Simulation results of the 94-species skeletal mechanism and the 74-species reduced mechanism show good agreement with that of the detailed mechanism for different phenomena such as ignition, extinction, laminar flame speed and homogeneous charge compression ignition combustion. [ABSTRACT FROM AUTHOR]

The approach for achieving super-high thermal efficiency in a gasoline homogeneous charge compression ignition lean-burn engine was studied using numerical simulation. A model engine was designed based on the split cycles, including the low-pressure cycle consisted of the turbocharger system and the high-pressure cycle controlled by the variable effective compression ratio (ε) and the exhaust gas recirculation (EGR). Based on the model engine, load (L) –Φoxy (F) – EGR (E) –ε (E) cooperative control strategy was proposed to optimize the thermal efficiency and its interactive mechanism was clarified. The results revealed that the core of the load (L) –Φoxy (F) – EGR (E) –ε (E) strategy was the simultaneous optimization of the combustion process and the specific heat ratio (γ) contributing to the piston work maximization. The optimum combustion phase was found in the range of 4°–9° crank angle after top dead center, and highest combustion rate under the rough combustion restriction was also required. Under this precondition, reducing ε to retard the combustion phase appropriately could mitigate the EGR usage to improve the γ. Based on the load (L) –Φoxy (F) – EGR (E) –ε (E) strategy, increasing the load was found to improve the thermal efficiency effectively by reducing the heat transfer loss. The highest brake thermal efficiency of 50% was reached when the gross indicated mean effective pressure was increased to 15 bar under the conventional engine condition. Further increasing the gross indicated mean effective pressure to 35 bar with elevated peak cylinder pressure of 400 bar could improve the brake thermal efficiency to 54% under the enhanced mechanical strength condition. To pursue super-high thermal efficiency, the approach of thermal insulation for the engine was proved to be more effective. It showed the potential to achieve the super-high brake thermal efficiency over 60% and maintain clean combustion by adopting the load (L) –Φoxy (F) – EGR (E) –ε (E) strategy in the model engine with thermal insulation and high mechanical strength. [ABSTRACT FROM AUTHOR]

The effects of exhaust gas recirculation (EGR) rate on homogeneous charge compression ignition (HCCI) combustion and emission of free-piston diesel engine generator (FPDEG) was investigated by using a three-dimensional (3-D) computational fluid dynamics (CFD) model of FPDEG. In the 3-D CFD model of FPDEG, the diesel mechanism with 109 species and 543 reactions was incorporated into the combustion model, and the soot and NOx production were calculated by Hiroyasu-NSC model and 12 steps NOx model. The simulation results showed that the EGR rate had great influence on the HCCI combustion and emission performance of FPDEG. As the EGR rate was changed from 0 to 10%, the HCCI combustion phase of FPDEG slightly lagged, the peak value of heat release, the maximum in-cylinder temperature and pressure and the NOx content significantly decreased, but SOOT content increased. When the EGR rate was 20%, the HCCI combustion of FPDEG was incomplete, and the UCH, SOOT and CO content all obviously increased. [ABSTRACT FROM AUTHOR]

The combustion and emission characteristics of surrogate diesel fuel homogeneous charge compression ignition (HCCI) with different combustion boundary conditions and n-butanol (NB) mixing ratios are studied in this work. Engine data of a two-stroke low-speed direct-injection marine diesel engine were selected for the reactor. HCCI combustion was achieved by compressing a completely homogeneous mixture of fuel and air. The results show that NO emissions decrease slightly with the increase of initial boundary pressure at a constant equivalence ratio and initial temperature. In addition, the different initial boundary temperature has little effect on NO emission. The results also indicate that the ignition delay time of the mixed fuel rises with the increase of n-butanol mixing ratio. The emissions and reaction rate of NOx reduce significantly with the increase of n-butanol percentage in surrogate diesel fuel and n-butanol mixing combustion at a constant equivalence ratio and total mole fraction. Meanwhile, CO2 emissions also decrease significantly with the increase of n-butanol mixing ratio.

Heat transfer has a profound influence on homogeneous charge compression ignition combustion. When a thermal barrier coating is applied to the combustion chamber, the insulating effect magnifies the wall temperature swing, decreasing heat transfer during combustion. This enables improvements in both thermal and combustion efficiency without the detrimental impacts of intake charge heating. Increasing the temperature swing requires coatings with lower thermal conductivity and heat capacity. A promising avenue for simultaneously decreasing both thermal conductivity and capacity is to increase the porosity fraction. A proprietary solution precursor plasma spray process enables discrete organization of the porosity structure, called inter-pass boundaries, which in turn produces a step-reduction in thermal conductivity for a given porosity level. In this investigation, yttria-stabilized zirconia is used to create four different thermal barrier coatings to study the potential of structured porosity as means of improving the "temperature swing" behavior in a homogeneous charge compression ignition engine. The baseline coating is "dense YSZ," applied using a standard air-plasma spray process. Next, significant reductions of the thermal conductivity are achieved by utilizing the solution precursor plasma spray process to create inter-pass boundaries with a moderate overall porosity. Performance, efficiency, and emissions are compared against both a baseline configuration with a metal piston and an air-plasma spray "dense YSZ" coating. Experiments are carried out in a single-cylinder gasoline homogeneous charge compression ignition engine with exhaust re-induction. Experiments indicate that incorporating structured porosity into thermal barrier coatings produces tangible gains in combustion and thermal efficiencies. However, there is an upper limit to porosity levels acceptable for homogeneous charge compression ignition engine application because an elevated porosity fraction leads to excessive surface roughness and undesirable fuel interactions. Comparison of the coatings showed the best results with coating thickness of up to 150 µ m. Thicker coatings led to slower surface temperature response and attenuated swing temperature magnitude. [ABSTRACT FROM AUTHOR]

This paper experimentally and numerically studied the effects of fuel combination and intake valve opening (IVO) timing on combustion and emissions of an n-heptane and gasoline dual-fuel homogeneous charge compression ignition (HCCI) engine. By changing the gasoline fraction (GF) from 0.1 to 0.5 and the IVO timing from −15°CA ATDC to 35°CA ATDC, the in-cylinder pressure traces, heat release behaviors, and HC and CO emissions were investigated. The results showed that both the increased GF and the retarded IVO timing delay the combustion phasing, lengthen the combustion duration, and decrease the peak heat release rate and the maximum average combustion temperature, whereas the IVO timing has a more obvious influence on combustion than GF. HC and CO emissions are decreased with reduced GF, advanced IVO timing and increased operational load. [ABSTRACT FROM AUTHOR]

When compared to traditional engines, homogeneous charge compression ignition has the potential to significantly reduce NOx raw emissions, while maintaining a high fuel efficiency. Homogeneous charge compression ignition is characterized by compression-induced autoignition of a lean homogeneous air--fuel mixture. Since homogeneous charge compression ignition does not utilize direct ignition control, it is strongly dependent on the state of the cylinder charge and can suffer from high cyclic variability. With spark-assisted compression ignition, it has been demonstrated that misfires can be reduced, while preserving the high thermal efficiency of homogeneous charge compression ignition as a result of the more favorable physical mixture properties due to dilution. However, spark-assisted compression ignition reduces the NOx benefits of homogeneous charge compression ignition, as it increases the local combustion temperatures. To merge the advantages of the homogeneous charge compression ignition and the spark-assisted compression ignition combustion processes, a field-programmable gate array for detailed simulation of the physical gas exchange is combined with a rapid spark system. The low latency and computational speed of the field-programmable gate array allows the simulation process to be implemented in real time. When combined with the rapid reaction time of the high-frequency current-based rapid ignition system, a feedforward controller based on the cylinder pressure or heat release is realized. The developed model-based controller determines if a spark is required to assist the homogeneous charge compression ignition combustion process. The use of the field-programmable gate array and rapid ignition system allows for the calculation of combustion properties and controller output within 0.1 °CA. This article presents the development and experimental validation of the developed controller on a single-cylinder research engine. The combustion stability has been significantly improved as reflected in an improved standard deviation of the indicated mean effective pressure and a reduction of the combustion phasing variations. Furthermore, compared to a traditional homogeneous charge compression ignition system, the hydrocarbon emissions can be reduced, while maintaining low NOx emissions. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition combustion is highly dependent on in-cylinder thermal conditions that are favorable to auto-ignition, and the presence of deposits can dramatically impact the in-cylinder environment. Because fuels available at the pump can differ considerably in composition, and fuel composition and the included additive package directly affect how deposits accumulate in a homogeneous charge compression ignition engine, strategies intended to bring homogeneous charge compression ignition to market must account for this fuel and additive variability. In order to investigate this impact, two oxygenated refinery stream test fuels with two different additives were run in a single cylinder homogeneous charge compression ignition engine. The two fuels had varying chemical composition; one represents a ‘‘dirty’’ fuel with high aromatic content that was intended to simulate a worst-case scenario for deposit growth, while the other represents a California Reformulated Gasoline Blendstock for Oxygenate Blending fuel, which is the primary constituent of pump gasoline at fueling stations across the state of California. The additive packages are typical of technologies that are commercially available to treat engine deposits. Both fuels were run in an experimental, single-cylinder homogeneous charge compression ignition engine in a passive conditioning study, during which the engine was run at steady state over a period of time in order to track changes in the homogeneous charge compression ignition combustion event as deposits accumulated in-cylinder. Both the composition and the additive influenced the structure of the combustion chamber deposit layer, but more importantly, both the rate at which the layer developed and the equilibrium thickness it achieved. The overall thickness of the combustion chamber deposit layer was found to have a significant impact on homogeneous charge compression ignition combustion phasing. [ABSTRACT FROM AUTHOR]

High heat release rates limit the operating range of homogeneous charge compression–ignition engines to low and medium loads. Thermal stratification has been shown to stagger autoignition, lower heat release rates, and extend the operating range of homogeneous charge compression–ignition engines. However, the dependence of naturally occurring thermal stratification on the engine size, speed, and internal residual dilution is not fully understood. A three-dimensional computational fluid dynamics model with large eddy simulations and detailed chemical kinetics was developed using CONVERGE. This model was used to simulate two different engines: (1) a light-duty 2.0 GM Ecotec Engine modified for homogeneous charge compression–ignition combustion in one of the cylinders and (2) a medium-duty Cummins B-series engine modified for homogeneous charge compression–ignition combustion in one of the cylinders. For the light-duty engine, five consecutive modeled cycles were compared with experimental data from 300 consecutive cycles using residual gas dilution at 2000r/min. For the medium-duty engine, five consecutive modeled cycles were compared with experimental data from 100 consecutive cycles using air dilution with intake heating at 1200r/min. In the light-duty engine, it was found that incomplete mixing between fresh charge and residual gas increased thermal stratification early in the compression stroke for residual dilution compared to air dilution. Residual stratification at the onset of ignition was small and not directly coupled with thermal stratification. Heat losses to the walls were the dominant source of thermal stratification at the onset of ignition. The reduced oxygen concentration due to residual dilution, increased the temperature requirement for autoignition, which increased heat transfer losses and increased the thermal stratification around top dead center. The thermal stratification before ignition reduced when the engine speed increased because of the lower heat transfer losses. The light-duty engine was found to have larger portion of the fuel energy lost to heat transfer than the medium-duty engine, which resulted in larger thermal stratification before ignition. [ABSTRACT FROM AUTHOR]

A reciprocating engine without a crank-slider mechanism is called a free-piston engine. If the piston is directly connected to a linear alternator, it is called a free-piston linear alternator . Free-piston engines and free-piston linear alternators have the potential to offer solutions for future hybrid electric vehicles and stationary power generation, by enabling direct conversion of mechanical energy to electricity. They benefit from reduced friction losses compared to conventional engines and can have variable compression ratio, which enables combustion control and optimization. Their widespread application has been limited by the necessity for high-speed control strategies. However, their operating characteristics can provide high efficiency, especially when used with low temperature combustion strategies. Low temperature combustion combines the high thermal efficiency of diesel engines, with the low soot emissions of spark-ignition engines, and low NOx emissions because of low burned gas temperatures. This article provides a comprehensive review of free-piston engine technology, with a focus on advanced combustion processes and their potential for use in future powertrain systems. [ABSTRACT FROM AUTHOR]

Homogeneous charge compression ignition has the potential to significantly reduce NOx emissions, while maintaining a high fuel efficiency. Homogeneous charge compression ignition is characterized by compression-induced autoignition of a lean homogeneous air-fuel mixture. Combustion timing is highly dependent on the in-cylinder state including pressure, temperature and trapped mass. To control homogeneous charge compression ignition combustion, it is necessary to have an accurate representation of the gas exchange process. Currently, microprocessor-based engine control units require that the gas exchange process is linearized around a desired operating point to simplify the model for real-time implementation. This reduces the models' ability to handle disturbances and limits the flexibility of the model. However, using a field programmable gate array, a detailed simulation of the physical gas exchange process can be implemented in real time. This paper outlines the process of converting physical governing equations to an offline zero-dimensional gas exchange model. The process used to convert this model to a field programmable gate array capable model is described. This model is experimentally validated using a single cylinder research engine with electromagnetic valves to record realtime field programmable gate array gas exchange results and comparing to the offline zero-dimensional physical model. The field programmable gate array model is able to accurately calculate the cylinder temperature and cylinder mass at 0.1 CA intervals during the gas exchange process for a range of negative valve overlaps, boost conditions and engine speeds making the model useful for future real-time control applications. [ABSTRACT FROM AUTHOR]

Principal component transport-based data-driven reduced-order models (PC-transport ROM) are being increasingly adopted as a combustion model of turbulent reactive flows to mitigate the computational cost associated with incorporating detailed chemical kinetics. Previous studies were mainly limited to replicating relatively-simple chemistry in canonical configurations. The objective of the present study, therefore, is to further explore the accuracy of PC-transport ROM on more complex combustion phenomenon where, for example, large hydrocarbon fuel chemistry spanning a broad range of thermochemical space governs sequential multi-stage compression ignition processes. The cumulative error of PC-transport for this problem, and for others that depend upon sequential highly nonlinear physics, has to be minimal as the combustion phasing and heat release rate in internal combustion engines depends upon accurate predictions of minor ignition species whose concentrations start from ashes and grow orders of magnitude over the course of low- and high-temperature autoignition. Specifically, the PC-transport ROM is applied to predict the compression ignition characteristics of lean n -heptane/air and primary reference fuel (PRF)/air mixtures in a two-dimensional (2-D) constant volume computational domain initialized with a two-dimensional isotropic turbulence spectrum and temperature inhomogeneities. PCA is used to define the low-dimensional manifold that represents the original thermochemical state vector, and artificial neural network (ANN) models are adopted to tabulate chemical kinetics, transport, and thermodynamic properties. A series of 2-D pseudo-turbulent simulations are performed at engine pressures by varying the initial mean and r.m.s. of temperature, turbulence intensity, and the composition of fuel/air mixture. The results show that the PC-transport ROM accurately reproduces the instantaneous and statistical ignition characteristics of the fuel/air mixture, aided by pre-processing techniques including species subsetting, data clustering, and data transformation. It is found that PCs are not properly scaled with a power transformer if reactants are included in the species subset, which leads to a decrease in the accuracy of the PC-transport ROM. A separation of the reactants from the species subset ensures that the temporal evolution of the PCs starts from zero and spans orders of magnitude with time, and as such, this approach is found to effectively redistribute both PCs and their source terms with a power transformer. The computational speed-up factor of the PC-transport ROM ranges between 5.1 and 15.0 for the cases with n -heptane/air mixture and PRF/air mixture, respectively. Moreover, a potential further speed-up is anticipated through a combination of reduction in grid resolution requirements and in the stiffness of the chemical system. As an example, many of the pre-processing methods for inhomogeneous compression ignition may also apply to other complex intermittent combustion phenomena. Novelty and significance statement • The PCA-based reduced-order model (PC-transport ROM) has been applied to the multi-stage compression ignition of large hydrocarbon fuels under HCCI-relevant conditions. The present work presents a systematic procedure to accurately capture the two-stage ignition behavior of lean n -heptane/air or PRF50/air mixture. • The present work demonstrates an advantage of the PC-transport ROM in terms of computational speed-up. The computational speed-up factor for the ROM is up to 15, and moreover, a potential additional speed-up is anticipated through the reduction in the spatial and temporal resolution required. • A series of 2-D PC-transport ROMs are conducted to demonstrate the robustness of the ROM. A limitation of the ROM against different operating conditions is also discussed. [ABSTRACT FROM AUTHOR]

The thermal efficiency of an efficient gasoline engine is only about 40% and it will produce a large number of harmful products. Curbing harmful emissions and enhancing thermal efficiency have always been the goals pursued and emission regulations are also being tightened gradually. As one of the main consumers of fossil fuels, automobile engines must further reduce fuel consumption and emissions to comply with the concept of low-carbon development, which will also help them compete with electric vehicles. Homogeneous charge compression ignition (HCCI) combustion combined with variable valve actuation (VVA) technology is one of the important ways to improve engine emissions and economy. HCCI combustion based on VVA can only be realized at small and medium loads. The actual application on the entire vehicle needs to be combined with spark ignition (SI) combustion to achieve full working condition coverage. Therefore, HCCI combustion needs fast valve response characteristics; however, the valve lift and timing of the existing VVA mechanisms are mostly controlled separately, resulting in poor valve response. In order to solve this problem, the cam driven hydraulic variable valve actuation (CDH-VVA) mechanism was designed. The valve lift and timing can be adjusted at the same time and the switching of valve lift and timing can be completed in 1~2 cycles. A set of combustion mode switching data is selected to show the response characteristics of the CDH-VVA mechanism. When switching from spark ignition (SI) to HCCI, it switches to HCCI combustion after only one combustion cycle and it switches to stable HCCI combustion after two combustion cycles, which proves the fast response characteristics of the CDH-VVA mechanism. At the same time, the CDH-VVA mechanism can form the intake port exhaust gas recirculation (EGR), as one type of internal EGR. This paper studies the HCCI combustion characteristics of the CDH-VVA mechanism in order to optimize it in the future and enable it to realize more forms of HCCI combustion. At 1000 rpm, if the maximum lift of the exhaust valve (MLEV) is higher than 5.0 mm or lower than 1.5 mm, HCCI combustion cannot operate stably, the range of excess air coefficient (λ) is largest when the MLEV is 4.5 mm, ranging from 1.0~1.5. Then, as the MLEV decreases, the range of λ becomes smaller. When the MLEV drops to 1.5 mm, the range of λ shortens to 1.0~1.3. The maximum value of the MLEV remains the same at the three engine speeds (1000 rpm, 1200 rpm and 1400 rpm), which is 5.0 mm. The minimum value of the MLEV gradually climbs as the engine speed increase, 1000 rpm: 1.5 mm, 1200 rpm: 2.0 mm, 1400 rpm: 3.0 mm. With the increase of engine speed, the range of indicated mean effective pressure (IMEP) gradually declines, 3.53~6.31 bar (1000 rpm), 4.11~6.75 bar (1200 rpm), 5.02~6.09 bar (1400 rpm), which proves that the HCCI combustion loads of the intake port EGR are high and cannot be extended to low loads. The cyclic variation of HCCI combustion basically climbs with the decrease of the MLEV and slightly jumps with the increase of the engine speed. At 1000 rpm, when the MLEV is 5.0 mm, the cyclic variation range is 0.94%~1.5%. As the MLEV drops to 1.5 mm, the cyclic variation range rises to 3.5%~4.5%. Taking the maximum value of the MLEV as an example, the cyclic variation range of 1000 rpm is 0.94%~1.5%, 1200 rpm becomes 1.5%~2.3% and 1400 rpm rises to 2.0%~2.5%.