Homogeneous Charge Compression Ignition Engine Research Articles

Natural gas-fueled HCCI engine performance and emission analysis and comparison with SI and spark-assisted operations

ABSTRACT The homogeneous charge compression ignition (HCCI) engine is a promising technology in terms of both soot and NOx emission. Natural gas (NG) is advantageous especially for HCCI engines with its single stage combustion, low C/H ratio, and high octane number. Since the main challenge of HCCI technology is stability and transient operations, using HCCI for constant speed operations may be advantageous. In this study, a CI diesel engine, which is used as a generator at constant speed, was modified and converted into an NG-fuelled, SI engine. Then, the engine was supplied with NG for SI, HCCI, and spark-assisted HCCI experiments. Spark-assisted operations were executed by using 3, 5, and 7 degree ignition advance values to assist HCCI combustion. In-cylinder pressure variations, exhaust temperature, specific fuel consumption, and emission values were investigated for comparison of different strategies. Experimental results showed that using the HCCI strategy and retardation of ignition advance of spark-assisted HCCI operations reduced maximum pressure. Therefore, these strategies improved NOx emissions, while HC emissions were slightly increased. The spark-assisted HCCI strategy improves the stability of operation while increasing CO emission. The specific fuel consumption value of HCCI was slightly higher than that of SI operation, while it was lower than spark-assisted strategies.

Exergetic investigation of the influence of injector location in HCCI engines utilizing DEE as pilot fuel and biogas as primary fuel

To address the global demand for sustainable energy, integrating biogas into internal combustion engines is becoming more important. Homogeneous Charge Compression Ignition (HCCI) engines, known for high efficiency and low emissions, offer a promising solution. This study investigates the optimal injector location for using biogas in HCCI engines, with diethyl ether (DEE) as the pilot fuel, evaluating three positions: (i) at the port, (ii) 6 cm away (Manifold 1), and (iii) 10 cm away (Manifold 2). Through experiments and simulations, the impact of injector location on engine performance is analyzed across various parameters, including methane fractions, engine loads, and exhaust gas compositions. Results show that port injection achieves the highest first law and exergy efficiencies but increases emissions of hydrocarbons (HC), carbon monoxide (CO), and smoke. At 15 Nm load, Manifold 1 shows a 27.34 % reduction in exergy efficiency compared to port injection, while Manifold 2 exhibits an 18.49 % decrease at higher loads. Despite lower efficiencies, Manifold 1 effectively reduces harmful emissions. The study also considers exergo-economic and sustainability aspects, highlighting that while port injection is optimal for efficiency, Manifold 1 excels in minimizing HC and CO emissions, with a 50 % reduction in HC and 71.43 % reduction in CO emissions at 15 Nm load compared to port injection. Manifold 2 achieves the lowest smoke emissions across all loads. This investigation provides crucial insights into optimizing HCCI engines for biogas utilization, emphasizing injector location, fuel composition, and operating parameters to enhance performance and reduce environmental impact.

Effect of direct water injection timing and quantity on combustion, performance, and emission characteristics of a homogeneous charge compression ignition engine − A CFD analysis

Direct water injection in an HCCI engine is a promising strategy to extend the operating load limit. The advantage of water injection depends on the percentage of water evaporated inside the cylinder, which further depends on the time available for the evaporation and the interaction of water spray plumes with the in-cylinder air-flow field. Here, CFD investigations are done to find the effect of water injection timing (WIT) and quantity on the load limit and performance and emission characteristics of the HCCI engine. Various WITs are considered for the study, varying from 100° CA before TDC to 20° CA before TDC. The water-to-fuel ratio is varied from 0 to 1 in steps of 0.2. A three-dimensional computational fluid dynamics model is used for the study, and CFD models used are validated from the available experimental data in the literature. The results show that WITs before 650° CA and after 670° CA are inappropriate for the HCCI engine, as heat release rate and MRPR are high in these cases. Also, the evaporation rate of water increases when the water injection is done in the region where the direction of the air-flow field is opposite to the direction of water injection. At the WIT of 60°, the HRR and MRPR are minimal, and the water vapor distribution is good compared to other cases. Also, it is seen that a water-to-fuel ratio of 0.8 gives more scope for extending the upper load limit with a marginal penalty of the IMEP; hence, a WIT of 60° with the water-to-fuel ratio of 0.8 is considered optimum. With the optimum case, it is feasible to increase the ER from 0.74 to 0.95, resulting in an increase of IMEP from 3.23 bar to 4.92 bar, which is 52.3 % more than without a water injection case at the ER of 0.74. Also, it showed minimum NOx emissions in all the water injection cases. Hence, these results address the primary challenges associated with HCCI engines, demonstrating that direct water injection can substantially improve the combustion controllability and operational range of HCCI engines.

Computational analysis of ammonia-hydrogen blends in homogeneous charge compression ignition engine operation

Ammonia (NH3) is considered a promising alternative fuel due to its renewable and carbon-free nature. The addition of hydrogen (H2) significantly improves its flammability, making it suitable for use in internal combustion engines. The homogeneous charge compression ignition (HCCI) technique offers a practical solution for high-efficiency NH3-H2 operation, but it is not extensively discussed in existing literature. To enhance the understanding of NH3-H2 HCCI engines, this study employs a zero-dimensional model validated against experimental results to investigate engine efficiency and nitrogen oxides (NOx) emissions. The results indicate that an ammonia-dedicated HCCI mode would misfire at a 22:1 compression ratio and an engine speed of 1500 rpm if the intake pressure and temperature are insufficient. Hydrogen addition can help overcome the misfire issue and reduce the intake pressure and temperature required for combustion initiation. However, higher hydrogen addition ratios decrease thermal efficiency and increase NOx emission levels. In lean NH3-H2 HCCI operation, NOx emissions are primarily driven by fuel-borne mechanisms and peak at an equivalence ratio of around 0.5. A higher hydrogen addition ratio should be avoided as it increases the risk of ringing, thereby reducing the maximum allowable equivalence ratio and engine load. As a result, a moderate hydrogen addition ratio, such as 20 %, is preferable for NH3-H2 HCCI engines. Additionally, an equivalence ratio of approximately 0.3 is optimal, balancing multiple performance indicators such as thermal efficiency, NOx emission levels, and engine operating stability. These findings suggest that the operating range of NH3-H2 HCCI engines is limited, making them more suitable for off-road applications, such as power generation.

The Green Energy Effect on an HCCI Engine from Used Cooking Oil-based Biodiesel from Malaysia

Emissions from internal combustion engines (ICEs) significantly impact the environment, leading continents worldwide to work towards reducing them. The industry is increasingly leaning towards electric powertrains. However, power plants still utilize ICEs as generators, contributing to global pollution. Consequently, ICE emissions are garnering international attention. Alternatives like the Homogeneous Charge Compression Ignition (HCCI) engine and biodiesel fuels are being explored. HCCI engines have not been extensively tested with Used Cooking Oil (UCO) biodiesel. This study investigates the performance and emissions of HCCI engines using UCO-based biodiesel. This study tested an air-cooled, single-cylinder, 4-stroke diesel engine operating at 3600 rpm with a displacement of 0.219 liters. The HCCI mode was activated during preheating and run at 2700 rpm under varying biodiesel blend percentages and intake temperatures. In HCCI mode, brake-specific fuel consumption (BSFC) increased, peaking at a 90°C intake temperature. Diesel fuel in-cylinder pressure reached a maximum of 81 bars at 90°C, decreasing to 79 bars at 70°C. The HCCI mode resulted in lower NOx, CO, and UHC emissions. Higher biodiesel blend ratios further reduced CO emissions. Raising the intake air temperature to 90°C lowered NOx emissions by 96.66%, from 150 ppm to 5 ppm. Using green energy sources as fuel in HCCI engines significantly reduced emissions in this study, suggesting their potential as a future fuel for advanced engines.

Evaluating the feasibility of machine learning algorithms for combustion regime classification in biodiesel-fueled homogeneous charge compression ignition engines

The present study explores the feasibility of machine-learning algorithms in classifying the combustion regimes in a homogenous charge compression ignition (HCCI) engine fueled with biodiesels from diverse sources. A distinctive feature of this research is the extensive database of HCCI combustion regimesgenerated for neat biodiesel fuels of different compositions. The engine experiments reveal significant variability in the load range of operation of HCCI engines across different biodiesel fuels. Strategies including compression ratio variation and charge dilution were employed to achieve higher engine loads, and the results confirm that the interplay of fuel reactivity and engine load, along with compression ratio and charge dilution, dictates the combustion stability. This complex phenomenon necessitates ascertaining the prevailing combustion type under a given engine load for biodiesel fuels derived from diverse sources. Thus, the present study aims to investigate the applicability of machine learning algorithms for developing models that classify combustion regimes in a neat biodiesel-fueled light-duty HCCI diesel engine. Models are developed to categorize biodiesel HCCI combustion into four groups: engine misfire, stable combustion without dilution, stable combustion with dilution, and knocking combustion. Biodiesel composition (13 different methyl esters), compression ratio and engine load are considered the input variables for the machine learning (ML) models. The results show that Naive Bayes and logistic regression models exhibit poor applicability among the investigated ML models due to a low F1 score (<0.8). The k-NN and SVM models demonstrate practical suitability with reasonably good F1 scores. However, the decision tree model outperforms all, precisely classifying 94 % of calibration and validation samples. It could precisely classify all the validation samples corresponding to misfire combustion, 21 of 22 samples to stable combustion, 4 of 6 samples to stable combustion with dilution, and 30 of 31 to knocking combustion. Thus, it emerges as the best approach to classify the combustion regimes of HCCI engines operated with neat biodiesel fuels.

Improving the combustion process of a homogeneous charge compression ignition engine running with triple fuel blend using response surface methodology

Improving the combustion process of a homogeneous charge compression ignition engine running with triple fuel blend using response surface methodology

Auto-Ignited Combustion Control in an Engine Equipped with Multiple Boosting Devices

&lt;div&gt;The combustion timing of auto-ignited combustion is determined by composition, temperature, and pressure of cylinder charge. Thus, for a successful auto-ignition, those key variables must be controlled within tight target ranges, which is challenging due to (i) nature of coupling between those variables, and (ii) complexity of managing multiple actuators in the engine. In this article, a control strategy that manages multiple actuators of a boosted homogeneous charge compression ignition (HCCI) engine is developed to maintain robust auto-ignited combustion. The HCCI engine being considered is equipped with multiple boosting devices including a supercharger and a turbocharger in addition to conventional actuators and sensors. Since each boosting device has its own pros and cons, harmonizing those boosting devices is crucial for successful transient operation. To address the multi-variable transient control problem, speed-gradient control methodology is applied to minimize coupling between boosting devices. Simulation results show that the control strategy overcomes turbo lag by utilizing the supercharger during transient. The controller developed is still appliable to manage multiple boosting devices with conventional engines as well as HCCI engine.&lt;/div&gt;

Effect of water injector location on combustion and performance of an HCCI engine - A CFD analysis

A homogeneous charge compression ignition (HCCI) engine is capable of producing high thermal efficiency with very low emissions. However, because of the limited upper load level constrained by knocking, the HCCI engine is not yet commercialized. Water injection can tackle this issue, enhancing the upper load limit without excessive heat release rate. However, the effectiveness of water injection depends on in-cylinder water evaporation, which in turn depends on water injection parameters. Therefore, this study is conducted to study the effect of water injector location on the combustion and performance characteristics of an HCCI engine by a computational fluid dynamic (CFD) analysis. The engine specifications and boundary conditions are taken from the literature. A three-dimensional computational fluid dynamics (3D CFD) model was developed using CONVERGE CFD coupled with detailed chemical kinetics to gain a better understanding of the phenomena of water injection in an HCCI engine. The CFD models used are validated from the available experimental data in the literature for the engine considered. Here, the water injector location is optimized based on the Water vapor distribution within the cylinder, nitric oxide (NOx) emissions, and maximum rate of pressure rise (MRPR). The results show that the water injector at 37 mm from the center of the cylinder gives better results than in other cases considered. With the optimum water injector location, the indicated mean effective pressure is increased by about 35.91% than without the water injection case. This study will be helpful in the development of HCCI engines.

Advancements in homogeneous charge compression ignition technology: Efficiency, emissions, and applications in the modern automotive industry

Homogeneous charge compression ignition (HCCI) technology is a novel approach in internal combustion engines that combines the efficiency of gasoline engines with the spontaneous ignition characteristics of diesel engines. HCCI engines offer cleaner emissions, reduced noise, and wider fuel adaptability, overcoming many drawbacks of traditional engines. The paper explores the HCCI combustion process, highlighting its unique features and advantages over spark ignition (SI) and compression ignition (CI) engines. It also discusses innovations in HCCI technology, including its combination with other strategies like spark-controlled compression ignition (SCCI) and low-temperature combustion (LTC) to expand its load range. The challenges of HCCI technology, especially in combustion timing control, are addressed, along with suggestions for future research directions. The application of HCCI technology for energy savings and emission reduction and its impact on the automotive industry are also discussed, citing examples from manufacturers like Volvo, Nissan, and General Motors. The paper concludes by emphasizing the importance of ongoing research, integration with other technologies, and financial support to further advance HCCI technology and its market potential.

Computational Fluid Dynamics (CFD) Validation and Investigation the Effect of Piston Bowl Geometries Performance on Port Fuel Injection-Homogeneous Charge Compression Ignition (PFI-HCCI) Engines

Computational Fluid Dynamics (CFD) Validation and Investigation the Effect of Piston Bowl Geometries Performance on Port Fuel Injection-Homogeneous Charge Compression Ignition (PFI-HCCI) Engines

Experimental Study of a Homogeneous Charge Compression Ignition Engine Using Hydrogen at High-Altitude Conditions

One of the key factors of the current energy transition is the use of hydrogen (H2) as fuel in energy transformation technologies. This fuel has the advantage of being produced from the most primary forms of energy and has the potential to reduce carbon dioxide (CO2) emissions. In recent years, hydrogen or hydrogen-rich mixtures in internal combustion engines (ICEs) have gained popularity, with numerous reports documenting their use in spark ignition (SI) and compression ignition (CI) engines. Homogeneous charge compression ignition (HCCI) engines have the potential for substantial reductions in nitrogen oxides (NOx) and particulate matter (PM) emissions, and the use of hydrogen along with this kind of combustion could substantially reduce CO2 emissions. However, there have been few reports using hydrogen in HCCI engines, with most studies limited to evaluating technical feasibility, combustion characteristics, engine performance, and emissions in laboratory settings at sea level. This paper presents a study of HCCI combustion using hydrogen in a stationary air-cooled Lombardini 25 LD 425-2 modified diesel engine located at 1495 m above sea level. An experimental phase was conducted to determine the intake temperature requirements and equivalence ratios for stable HCCI combustion. These results were compared with previous research carried out at sea level. To the best knowledge of the authors, this is the first report on the combustion and operational limits for an HCCI engine fueled with hydrogen under the mentioned specific conditions. Equivalence ratios between 0.21 and 0.28 and intake temperatures between 188 °C and 235 °C effectively achieved the HCCI combustion. These temperature values were, on average, 100 °C higher than those reported in previous studies. The maximum value for the indicated mean effective pressure (IMEPn) was 1.75 bar, and the maximum thermal efficiency (ITEn) was 34.5%. The achieved results are important for the design and implementation of HCCI engines running solely on hydrogen in developing countries located at high altitudes above sea level.

Computational investigation of equivalence ratio effects on performance and emissions in a dual-fuel homogeneous charge compression ignition (HCCI) engine with 90% n-dodecane and 10% ethanol

As the automotive industry seeks environmentally friendly and fuel-efficient solutions, a significant transformation towards the Dual Fuel Homogeneous Charge Compression Ignition (DF-HCCI) Engine. It emerges as a highly promising and revolutionary approach to internal combustion engines. This paper provides a comprehensive Computational Investigation on the influence of Equivalence Ratio (ϕ) variations on the performance and emissions of a DF-HCCI engine, utilising a blend of 90% n-dodecane (premix) and 10% ethanol (spry injection). Through simulations, the study explores ϕ ranging from 0.45 to 0.70, providing a detailed analysis of their impact on crucial engine parameters. Results indicate a non-monotonic behaviour in piston work, with an initial increase followed by a decline beyond an optimal point due to incomplete combustion. CO emissions exhibit a general increase with higher ϕ, attributed to reduced air availability for complete combustion. CO2 emissions display a non-monotonic trend, peaking at ϕ = 0.5, indicative of a complex interplay between combustion temperature and completeness. NOx emissions decrease with rising ϕ, as higher temperatures favour NOx formation. Soot emissions decrease with increasing ϕ , correlating with lower combustion temperatures. This investigation provides insights into the relationship between ϕ and DF-HCCI engine characteristics, offering an optimising engine efficiency and mitigating environmental impact.

Effect of boundary on homogeneous charge compression ignition engine fueled with anode off-gas and refueled anode off-gas

Hybrid solid oxide fuel cells and internal combustion engine systems are one of the most efficient power plants for low-carbon fuels. But the utilization of anode off-gas was a challenge. Homogeneous charge compression ignition has the advantage for such dilute and high-temperature fuels of 800 K∼ 1000 K and 80% inert gases, but easily influenced by intake temperature, pressure and composition. Based on 1-D model coupled with detail methane-air mechanism. Insights into engine performance combining thermodynamic trajectory and CA50 iso-contour on the PT domain for combustion of anode off-gas and refueled off-gas was provided. Results show that refueling strategy would benefit indicated mean effective pressure and misfire, but had little effect on thermal efficiency, and increase the possibility of knock and emissions by autoigniting in advanced and increased fuel reactivity. Exhaust gas recirculation strategy helped operate at low-temperature and low-pressure with refueling strategy. The overlapping safe zone implies the safe temperature and pressure for engine fueled with anode off-gas to add new fuel. As equivalence ratio increased, the thermal efficiency first increased and then decreased, peaking at 0.3. Although the combustion of the compression ratio of 17.1 is higher than that of the compression ratio of 8.2, the thermal efficiency and knock trend is worse.

Experimental and numerical investigation of methane combustion in a HCCI engine under enriched oxygen conditions

The challenge in the energy transition lies in the intermittent nature of renewable energy, requiring the development of effective storage methods. E-fuels are considered a promising solution, with potential applications to Homogeneous Charge Compression Ignition (HCCI) engines known for their high thermal efficiency and low nitrogen oxide emissions. However, HCCI engines face limitations such as low power density and a narrow operating range. To overcome these issues, oxygen-enriched combustion is proposed, aiming at enhancing the mixture reactivity and expanding the operating range by decreasing the intake temperature. As the potential of the expansion of the operating range has never been investigated, we performed an experimental campaign using a methane-fuelled HCCI engine at variable oxygen fractions in the oxidizer. To further elucidate the effects of oxy-fuel combustion, we also performed a kinetic analysis of the reactions driving the combustion behaviour. It has been experimentally found that increasing the oxygen content in the mixture, up to 90%, has a significant potential to decrease the needed intake temperature (up to 70 °C) of the charge to keep the Maximum Pressure Rise Rate (MPRR) below the safety threshold of 8 bar/CAD. Despite the notable IMEP increase achieved, operating the engine at high oxygen content presents significant technical challenges. Therefore, to make HCCI engines competitive with other combustion modes, it is essential to combine oxygen enrichment with additional power density enhancement techniques. The kinetic analysis has highlighted that the mixture is less sensitive to intake temperature changes at higher oxygen percentages (above 50%) and that the rates of the main reactions involved in methane and OH consumption are highly enhanced by oxygen addition.

Numerical study of piston bowl geometries on PFI-HCCI engine performance

Homogeneous charge compression ignition (HCCI) is an advanced combustion strategy proposed to provide higher efficiency and lower emissions than conventional compression ignition. However, there are still tough challenges in the successful operation of HCCI engines. Among these challenges, homogeneous mixture preparation and combustion phase control plays a vital role in determining the efficiency and emissions. Piston bowl geometry significantly enhances the process by improving the flow, turbulence, and mixing for the combustion. The study utilised experimental and numerical simulation methods to analyse HCCI combustion in port fuel injection (PFI) mode and evaluate the effect of piston geometries on engine performance. For this purpose, the different pistons bowl geometries (Baseline model, SQC, and CCC) with the same volume, compression, and equivalence ratio were numerically tested in a four-stroke, single-cylinder, YANMAR diesel engine. The numerical simulation results provide adequate assurance to proceed with the study with different piston geometries design. Compared to SQC and CCC, the Baseline model produced significantly higher cylinder pressure, temperature, and heat release rate. Different piston shape designs influenced the formation of air-fuel mixing, thereby affecting the time and location of onset combustion. The present investigation offered the significant role of piston geometry for the control mechanism of PFI-HCCI combustion, that is a vital part in demonstrating HCCI combustion.

Revolutionizing engine technology: The emergence and potential of novel engine materials

Concerns from both society and the government about the pollutants from automobile exhaust is becoming more and more noticeable in recent years. Compared with the engines mostly used currently, which are gasoline engines and diesel engines, the HCCI engine has ameliorated not only the problem of pollutant emissions but also efficiency to a large extent. This paper provides an in-depth analysis of Homogeneous Charge Compression Ignition (HCCI) engines. It first introduces the fundamental processes governing HCCI combustion and illustrates its working mechanism. While HCCI engines promise heightened efficiency, reduced emissions, and fuel versatility, they also present challenges such as combustion timing and related emissions. Commercial implementations by Nissan and Honda are discussed, shedding light on real-world applicability. Furthermore, the potential amalgamation of biodiesel with HCCI is explored, signaling a promising future for renewable fuels in advanced combustion engines. Despite the rise of hybrid vehicles, the unique benefits of HCCI position it as a significant player in future transportation. This paper emphasizes the necessity of ongoing research to overcome HCCIs challenges, ensuring it remains at the forefront of green automotive solutions.

Frictional Losses of Ring Pack in SI and HCCI Engine

The vast majority of research dedicated to enhancing the homogenous charge compression ignition (HCCI) low-temperature combustion system is focused on improving controllability, efficiency and emissions. This article aims to assess the impact of HCCI combustion on the operation of the piston ring system. Utilizing the measured pressures in the combustion chamber of a single-cylinder research engine operating in spark ignition (SI) and HCCI modes at various loads, simulations were carried out using an advanced ring pack model. This model integrates the gas flow, ring dynamics and ring mixed lubrication models. Simulations revealed that differences in the pressure above the piston between the HCCI and SI combustion significantly influence ring pack performance. The predicted energy losses due to the friction of piston rings against the cylinder liner are up to 5% higher in the HCCI engine than in the SI engine. This identified drawback diminishes the advantages of the HCCI engine resulting from higher thermal efficiency, and efforts should be made to minimize this negative impact.

The study on the conversion of single cylinder engine into homogeneous charge compression ignition (HCCI) engine

The study on the conversion of single cylinder engine into homogeneous charge compression ignition (HCCI) engine

Experimental study on combustion, performance, and emission characteristics of a homogeneous charge compression ignition engine fuelled with multiple biofuel-gasoline blends

For sustainable future mobility and power generation applications, there is a compelling need to develop flex-fuel engines that operate with multiple regional or season-specific biofuels. The present investigation focussed on mitigating agricultural diesel engines’ pollutant emission and performance problems. A systematic experimental study is carried out in a modified agricultural diesel engine to compare and evaluate the engine characteristics of the biofuel-gasoline blends fuelled Homogeneous Charge Compression Ignition (HCCI) mode. Seven different oxygenated biofuels: acetone, ethanol, methanol, isopropanol, isobutanol, ethyl acetate, and diisopropyl ether blended in gasoline, were investigated. 2-Ethylhexyl nitrate was used to improve the reactivity of fuel blends to the extent that lower engine loads could be reached. All the investigated biofuel-gasoline blends could produce permissible emission levels by suitably tuning the fuel proportions. The total nitrogen oxides and smoke emissions were below 2.8 and 0.0007 g/kWh, respectively, for all the investigated biofuel-gasoline blends at all the HCCI engine load conditions. The highest indicated thermal efficiency of 42% was attained using 60% ethanol/34% gasoline/6% 2-EHN blend in the HCCI engine at 4.63 bar BMEP (86% rated load), a notable 25% improvement compared to the conventional diesel engine. A detailed investigation was done to elucidate the HCCI engine performance (indicated thermal efficiency) trend variations with biofuel type and engine load. The Response Surface Method was adopted to correlate the maximum and the minimum engine load with the fuel composition and properties. The Desirability Approach provided the optimum fuel composition and properties to maximize the engine load range. The optimum solution achieved the engine load range of 20%–89% rated load. Overall, a compact, efficient, and clean HCCI combustion-based engine technology was developed that could be operated using multiple biofuels over an expanded load range.