Wyniki wyszukiwania - Biblioteka Nauki

1

Comparison of standard k-ε and RNG k-ε models in flows in 2d model of HCCI engine cylinder

100%

Ahmadi P. , Wyszynski M.

Archivum Combustionis

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2011

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tom Vol. 31 nr 1-2

79-96

EN

A computational study of flows in 2D model of four-stroke homogenous charge compression ignition (HCCI) engine cylinder was conducted by standard k-? and renormalization group (RNG) k-? models in FLUENTŽ release 6.2. The primary objective was to evaluate the aforementioned turbulence models for simulation of in-cylinder flows. The engine model was a 2D geometry of a cross section of piston-cylinder assembly, passing through the centres of intake and exhaust valves and parallel to the cylinder axis. Simulation was performed for five consecutive engine cycles under cold-flow assumption and with air as the working fluid. It is generally believed that standard k-? model over-predicts the turbulence kinetic energy, k. The results obtained from the fifth engine cycle at bottom dead centre (BDC) of the intake stroke revealed that below the intake valve and in the near-wall region, standard model estimates up to 26% higher values of k. Overestimation of k by the standard model, results in prediction of higher and less accurate values of turbulent viscosity, ? by this model. Subsequently, in-cylinder flows exhibit large rates of flow deformation, and by definition, RNG model predicts more accurate values of ? in rapidly strained flows. Below the intake valve, ? is predicted up to 53% lower by the RNG model. Therefore, RNG model, in comparison to standard model, is a better approach for computational investigation of in-cylinder flows.

2

Effects of combustion timing on pressure rise rates in a residual effected HCCI engine

99%

Hunicz J. , Gęca M. , Kordos P. , Rybak A.

Combustion Engines

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2019

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tom R. 58, nr 3

46--50

EN

Realization of a low temperature combustion concept in homogeneous charge compression ignition (HCCI) engines is a cutting-edge technology that offers clean combustion in parallel with high thermal efficiency. Low combustion temperature prevents from NOx formation whereas homogeneous mixture assures smokeless exhaust. However, achieving the production feasibility by HCCI technology is hampered by high pressure rise rates and the resulting combustion noise at a high load operation. This paper explores combustion timing parameters that are capable of maintaining permissible levels of pressure rise rates under a high load regime. On the basis of experimental data collected at a high load HCCI operation, pressure rise level was correlated with combustion duration. Furthermore, combustion duration has been found to scale with in-cylinder volume, for which 50% of mass fraction burned appeared. The results showed quantitatively limitations of engine load, pointing out on required combustion timings to achieve acceptable combustion harshness depending on engine load.

3

A thermo-kinetic model base study on natural gas HCCI engine response to different initial conditions

85%

Jazayeri S. , Omid J.

Silniki Spalinowe

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2009

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tom R. 48, nr 1

89-99

EN

Homogenous Charge Compression Ignition (HCCI) combustion is a promising concept to reduce engine emissions and fuel consumption. In this paper, a thermo-kinetic single zone model is developed to study the operation characteristics of a natural gas HCCI engine. The model consists detail chemical kinetics of natural gas oxidation including 325 reactions with 53 chemical species, and is validated with experimental results of reference works. Then, the influence of parameters such as manifold temperature/pressure, and equivalance ratio on incylinder temperature/pressure trends, start of combustion and heat release rate is studied. These results are explained in detail to describe the engine performance thoroughly.

PL

Zaletą silników wysokoprężnych o spalaniu homogenicznym (HCCI) jest możliwość zmniejszenia emisji związków toksycznych i zużycia paliwa. W artykule przedstawiono termokinetyczny jednostrefowy model silnika HCCI zasilanego gazem ziemnym. Model zawiera 325 reakcji chemicznych utleniania i jest skorelowany z wynikami doświadczalnymi uzyskanymi w innych badaniach. Przeanalizowano wpływ na pracę silnika takich parametrów, jak: temperatura i ciśnienie dolotu, współczynnik nadmiaru powietrza w cylindrze, zmiana temperatury i ciśnienia w cylindrze oraz początek zapłonu i szybkość wywiązywania się ciepła. Opisano rezultaty doświadczeń i ich wpływ na pracę silnika.

4

Effects of spark assist on HCCI combustion

85%

Hunicz J. , Gęca M. , Kordos P. , Medina A.

Combustion Engines

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2015

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tom R. 54, nr 2

73--77

EN

HCCI (homogeneous charge compression ignition) combustion is initiated by compression temperature and is independent of spark discharge. However, spark discharge can be applied under certain conditions to achieve hybrid combustion, where combustion by flame propagation is followed by auto-ignition of the unburned mixture. Spark assist can be applied to improve combustion stability at low loads or to reduce pressure rise rates under high load regime. In the current study variable spark ignition timing was applied for stoichiometric HCCI combustion, achieved using negative valve overlap technique. Under investigated conditions increase of nitrogen oxides emissions, due to flame propagation, was not observed. To provide more insight into combustion evolution, double Wiebe function was fitted to experimental heat release rates. It was found that only less than 10% of mixture was burned by flame propagation, even for very advanced spark discharge.

5

Boosted HCCI operation on multi cylinder V6 engine

80%

Misztal J. , Wyszyński M. , Xu H. , Tsolakis A. , Qiao J. , Wyszyński M. , Xu H. , Tsolakis A. , Qiao J. , Wilson T.

Journal of KONES

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2006

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tom Vol. 13, No. 2

315-321

EN

This paper is an extension of work done with boosted 1-cyl Homogenous Charge Compression Ignition (HCCI) engine. As has been proven in the authors’ laboratory on a single cylinder research engine, applying boosting can enable an increased load range with a decreased NOx emission. During the tests which are covered in this paper, a Jaguar V6 research engine with a negative valve overlap facility has been used. The engine is equipped with a mechanically coupled supercharger, which supplies the required amount of air. The introduction of a higher amount of air allows the cylinder mixture to be kept on a highly diluted level; this enables autoignition to be controlled and improves NOx emission. Finally, more air introduced into the cylinder enables more fuel to be injected, which in turn provides for a higher load. This fact is useful as one method to increase the upper load limit for HCCI. Boosted HCCI operation is very sensitive to exhaust gas residuals. It has been proven that valve operation, whether advancing or retarding away from the optimum point will affect NOx emission. Th6is paper will demonstrate that the optimisation of valve timing in connection with lambda value and boost pressure can produce lower NOx emission for the same or even a higher load.

6

Reduction of pressure rise rates in boosted HCCI engine using advanced valve actuation strategies

80%

Hunicz J. , Rybak A. , Gęca M.

Journal of KONES

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2018

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tom Vol. 25, No. 4

369--376

EN

Homogeneous Charge Compression Ignition (HCCI) is a promising low temperature combustion technology which offers high fuel efficiency and extremely low exhaust emissions. However, there are still some pending issues to be resolved before the technology will achieve mass production level. Namely, combustion controllability should be improved and HCCI operating range should be widen. The latter is constrained by excessive combustion rates under high loads. In this study, advanced variable valve actuation strategies were applied to control auto-ignition timings and combustion rates. The examinations were conducted using single-cylinder research engine fuelled with directly injected gasoline. The HCCI combustion was achieved using negative valve overlap technique. The engine was run under boosted conditions, in an operation regime where acceptable pressure rise rate (PRR) level is usually exceeded. Selected valve timing sweeps were carried out within a scope of the experiments to evaluate PRR reduction potential. The obtained results manifested superior combustion controllability. Late exhaust valve closing enabled reduction of the amount of internally re-circulated exhaust, which propagated to the main event combustion. From the intake side, two effects were observed, i.e. variability of the intake air aspiration and variability of the apparent compression ratio. Both phenomena were found to affect combustion timings and rates.

7

Application of Ion Current Measurement to Identification of Combustion Parameters in a Homogeneous Charge Compression Ignition Engine

80%

Hunicz J. , Filipek P. , Sobiesiak A.

Metrology and Measurement Systems

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2018

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tom Vol. 25, nr 1

223--234

EN

This study examines the application of ion current measurements to the identification of heat release parameters inside the combustion chamber of a homogeneous charge compression ignition (HCCI) engine fuelled with gasoline. HCCI combustion was achieved with the use of exhaust gas trapping. Combustion parameters derived from the in-cylinder pressure and ion current measurements were compared and analysed. Ion current measurements were accomplished using the existing spark plug and a dedicated electronic circuit. The experiments were performed at a variable excess air ratio and a variable amount of trapped residuals. The results showed a good correlation between peak values of the ion current and heat release rate, except for the cases where a fuel-rich mixture was burnt. The computed ion current integral over the volume of the combustion chamber showed a good agreement with the heat released in the combustion chamber, however this parameter was found to be affected by the amount of trapped residuals. Combustion timing characteristic values computed using heat release and ion current were found to be correlated, however the relationship was not linear.

8

Wpływ temperatury początkowej i składu mieszaniny palnej na pracę silnika HCCI zasilanego biogazem

71%

Motyl K. , Lisowski A.

Inżynieria Rolnicza

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2008

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tom R. 12, nr 1(99)

311-317

PL

W pracy przedstawiono wyniki badań wpływu temperatury początkowej i składu mieszaniny palnej na pracę silnika działającego według koncepcji HCCI. Stwierdzono, że istnieje określona wartość temperatury początkowej mieszaniny (około 200°C), po osiągnięciu której dalszy jej wzrost nie powoduje wyraźnego zwiększania ciśnienia maksymalnego spalania, prędkości narastania ciśnienia i opóźnienia samozapłonu. Wartość tej temperatury zależy nieznacznie od składu mieszaniny palnej.

EN

The paper presents results of the research carried out on the impact of initial temperature and combustible mixture composition on work of engine based on the HCCI principle. The researchers found that there is a specific value of the mixture initial temperature (approximately 200°C). When it is reached, further temperature rise does not cause any distinct increase of combustion process maximum pressure, pressure buildup rate and self-ignition delay. This initial temperature value slightly depends on combustible mixture composition.

9

Charakterystyki pracy silnika HCCI zasilanego biogazem

71%

Motyl K. , Lisowski A.

Inżynieria Rolnicza

|

2008

|

tom R. 12, nr 1(99)

303-310

PL

Na podstawie transformacji wykresów indykatorowych wyznaczono przebiegi zmian temperatury w komorze spalania, prędkości i skumulowanej ilości wydzielanego ciepła oraz sprawności spalania. Porównano ilość wydzielonego ciepła z ilością ciepła dostarczonego oraz przedstawiono wyniki pomiarów emisji toksycznego składnika spalin - NOx. Poziom tej emisji w silnikach HCCI jest znacznie niższy niż w silnikach konwencjonalnych zarówno o zapłonie iskrowym, jak i samoczynnym.

EN

Transformation of indicator diagrams provided grounds to determine trajectories of temperature changes in combustion chamber, speed and cumulated volume of released heat, and combustion efficiency. The researchers compared released heat volume with supplied heat volume, and presented measurement results for emissions of NOx - toxic exhaust gas component. This emission level for HCCI engines is much lower than for conventional engines, both spark ignition and spontaneous ignition.

10

A review of technical solutions for RCCI engines

71%

Szamrej G. , Karczewski M. , Chojnowski J.

Combustion Engines

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2022

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tom R. 61, nr 2

36--46

EN

Engines working in dual-fuel mode need special conditions to ignite air-fuel mixture without spark plug in a good moment with high combustion efficiency. To create homogenous air-fuel mixture the conditions in the cylinder are even more demanding. Many concepts of ignition was developed, but the most effective needs perfect mixing of fuel and air, which is a serious technical challenge. Technical solutions for dual-fuel engines cover the complexity of these problems thus leading to the further development of ignition systems in internal combustion engines. Fuel supply systems, the operation strategy of them, the shape of the combustion chamber are the most important elements to change and develop for correct operation of dual-fuel engines. The literature analysis showed a small amount of research carried out to optimize the operation of dual-fuel engines The variety of engines in which a dual-fuel system can be used requires much more research about them, and solutions necessary for their correctly operation.

11

A study of charge exchange in a residual-effected HCCI gasoline engine

71%

Hunicz J.

Silniki Spalinowe

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2011

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tom R. 50, nr 2

25-34

EN

An in-cylinder charge exchange process in a gasoline homogeneous charge compression ignition (HCCI) engine operated in a negative valve overlap (NVO) mode was studied. Research was performed using a single-cylinder research engine with fully variable valve actuation. Combination of in-cylinder pressure traces processing and fluid flow model enables cycle-by-cycle analysis of charge composition and temperature. It allows forecasting of in cylinder pressure volume and temperature-volume histories and can be used for physical-based engine control. In this paper influence of valves timings and valves lifts on the gas exchange process was analyzed. Special attention was paid to the effects of backflows of the in cylinder charge to an intake port.

PL

W artykule przedstawiono wyniki analizy procesu wymiany ładunku w benzynowym silniku HCCI (ang. Homogeneous charge compression ignition) działającym z ujemnym współotwarciem zaworów. Badania eksperymentalne zostały przeprowadzone na jednocylindrowym silniku badawczym wyposażonym w układ zmiany faz rozrządu i wzniosu zaworów. Połączenie analizy ciśnienia indykowanego w cylindrze i modelu przepływu czynnika roboczego pozwala na określanie składu oraz temperatury czynnika w cylindrze z rozdzielczością cyklową. Dzięki temu możliwe jest przewidywanie przebiegów krzywych temperatury i ciśnienia sprężania, co może być wykorzystane do sterowania silnika w oparciu o model fizyczny. W niniejszej pracy dokonano analizy wpływu zmiennych faz rozrządu i zmiennego wzniosu zaworów na proces wymiany ładunku. Szczególną uwagę zwrócono na efekty przepływów zwrotnych z cylindra do kanału dolotowego.

12

A research into a gasoline HCCI engine

71%

Hunicz J. , Niewczas A. , Kordos P.

Silniki Spalinowe

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2010

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tom R. 49, nr 1

3-13

EN

Homogeneous charge compression ignition (HCCI) is nowadays a leading trend in the development of gasoline internal combustion engines. The application of this novel combustion system will allow to comply with future legislations concerning the exhaust emissions including carbon dioxide. This paper presents a design and implementation of a research engine with a direct fuel injection and the capability of HCCI combustion via an internal gas recirculation and a negative valves overlap (NVO). The technical approach used in the engine allowed an autonomous HCCI operation at variable loads and engine speeds without the need of a spark discharge. Experiments were conducted at a wide range of valve timings providing data which allowed an assessment of a volumetric efficiency and exhaust gas recirculation (EGR) rate. Permissible range of air excess coefficient, providing stable and repeatable operation has also been identified. The use of direct gasoline injection benefited in the improvement of the start of the combustion (SOC) and heat release rate control via the injection timing.

PL

Kontrolowany samozapłon mieszanki paliwowo-powietrznej jest obecnie dominującym kierunkiem rozwoju silników benzynowych. Zastosowanie tego nowego systemu spalania pozwoli na spełnienie przyszłych norm emisji toksycznych składników spalin oraz dwutlenku węgla. W artykule przedstawiono konstrukcję silnika badawczego umożliwiającego realizację obiegu roboczego HCCI z wewnętrzną recyrkulacją spalin uzyskaną przez ujemne współotwarcie zaworów. Zastosowane rozwiązania techniczne umożliwiły autonomiczną pracę silnika w trybie HCCI przy zmiennych obciążeniach i prędkościach obrotowych, bez konieczności wspomagania zapłonu wyładowaniem iskrowym. Przeprowadzenie badań w szerokim zakresie zmian faz rozrządu pozwoliło na ocenę możliwości regulacji napełnienia cylindra i współczynnika reszty spalin. Określono także zakres współczynnika nadmiaru powietrza, w którym uzyskiwana jest stabilna i powtarzalna praca silnika. Zastosowanie bezpośredniego wtrysku benzyny do cylindra pozwoliło na rozszerzenie możliwości kontroli chwili samozapłonu i szybkości wywiązywania się ciepła przez regulację kąta początku wtrysku.

13

APPLICATION OF ION CURRENT MEASUREMENT TO IDENTIFICATION OF COMBUSTION PARAMETERS IN A HOMOGENEOUS CHARGE COMPRESSION IGNITION ENGINE

70%

Hunicz J. , Filipek P. , Sobiesiak A.

|

14

Formaldehyde for the premixed compression-ignition engine - an additive for ignition-timing control -

60%

Yamaya Y. , Furutani M. , Ohta Y.

Journal of KONES

|

2002

|

tom Vol. 9, No. 1-2

291-297

EN

Lean fuel/air mixtures with various fuel/fuel ratios between methane and n-butane were supplied to a premixed compression-ignition engine (i.e. homogeneous charge compression ignition engine, HCCI) with or without supplementary gaseous formaldehyde induction as an ignition controlling additive. In the no additive case the methane and butane function as the two fuels in the high/low-octane two-fuel premixed compression-ignition operation we proposed previously as another ignition control procedure. The formaldehyde addition to the methane/ butane/air mixtures has given the engine desired and stable ignition timings controllable by the amount of formaldehyde to be added, almost independent on the fuel/fuel ratios between methane and butane. The efficacy of formaldehyde has been confirmed as an ignition controlling medium for the piston-compression ignition of hydrocarbon/air mixtures.

15

Możliwości wykorzystania silnika pracującego na ładunku jednorodnym według koncepcji HCCI zasilanym biogazem

60%

Motyl K. , Lisowski A.

Ciepłownictwo, Ogrzewnictwo, Wentylacja

|

2008

|

tom R. 39, nr 2

27-30

PL

Przedstawiono wyniki badań wpływu temperatury początkowej i składu mieszaniny palnej na pracę silnika działającego według koncepcji HCCI. Badania przeprowadzono na jednocylindrowym wysokoprężnym silniku badawczym. Silnik badawczy był napędzany przez przekładnię pasową silnikiem elektrycznym, ze stałą prędkością obrotową 800 obr-min1. Temperatura początkowa mieszaniny zasilającej silnik zmieniała się w granicach 140 -210 °C. Skład mieszaniny był zmieniany w zakresie wartości współczynnika nadmiaru powietrza od [lambda] = 1 do [lambda] = 2. Silnik był zasilany gazem ziemnym o zawartości metanu 95%. Uzyskane wykresy indykatorowe silnika pozwoliły na ustalenie zależności: przebiegu ciśnienia maksymalnego spalania, prędkości narastania ciśnienia po samozapłonie i opóźnienia samozapłonu w funkcji temperatury początkowej mieszaniny i składu paliwa. Stwierdzono, że istnieje określona wartość temperatury początkowej mieszaniny (około 200 °C), po osiągnięciu której dalszy jej wzrost nie powoduje wyraźnego zwiększania ciśnienia maksymalnego spalania, prędkości narastania ciśnienia i opóźnienia samozapłonu. Wartość tej temperatury zależy nieznacznie od składu mieszaniny palnej.

EN

The investigation results of an influence of the initial temperature and gas composition mixture on the working mode of a HCCI engine are presented. The investigations were carried out with a single-cylinder high compression experimental engine. The engine was driven by using an electric motor via a transmission belt with a constant rotational speed of 800 rpm. The initial temperature of the feeding mixture was varied within the range of 140 -210 °C. The composition was also altered from [lambda]=1 to [lambda]=2. The natural gas with 95% of methane content was used as a fuel for the engine. The indicative diagrams, achieved for the engine, enabled an assessment of relationships between maximum combustion pressure, pressure increase after self-ignition and ignition delay as functions of the initial temperature of the mixture and fuel composition.

16

Compression Auto-Ignition Control in a 2-stroke Barrel-type Opposed-Piston Engine

60%

Pyszczek R. , Mazuro P. , Teodorczyk A.

Archivum Combustionis

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2017

|

tom Vol. 37 nr 1

25--42

EN

The aim of this study is to investigate a possibility of Compression Auto-Ignition (CAI) control in a turbocharged 2-stroke barrel type Opposed-Piston (OP) engine fueled with a gasoline. The barrel type OP engine arrangement is of particular interest for the authors because of its robust design, high mechanical efficiency and relatively easy incorporation of a Variable Compression Ratio (VCR). A 3D CFD numerical simulations of the scavenging and combustion processes were performed with use of the AVL Fire solver that is based on a Finite Volume Method (FVM) discretization and offers a number of tools dedicated to numerical simulations of working processes in internal combustion engines. The VCR and water injection were considered for the ignition timing control. A number of cases was calculated with different engine compression ratios, different equivalence ratios and different amount of injected water. Results show that proposed measures should be appropriate for controlling the CAI combustion process. Furthermore, application of these solutions in the real engine can significantly contribute to increase in efficiency and decrease in emissions.

17

Facilitation of HCCI combustion of biogas at moderate compression ratios by application of fuel reforming and inlet air heating

60%

Wyszynski M. L. , Megaritis A. , Karlovsky J. , Yap D. , Peucheret S. , Lehrle R. S. , Xu H. , Golunski S.

Journal of KONES

|

2004

|

tom Vol. 11, No. 3-4

347-356

EN

The HCCI shows large benefits in NOx emissions and fuel economy, but is difficult to achieve and control in engines with moderate compression ratios when natural gas and particularly biogas are used as fuel. It has been shown in literature that the addition of hydrogen translates into the lowering of the auto-ignition temperature during the combustion stroke. A major efforts is being devoted to developing further the fuel reforming technology which facilitates the auto-ignition of hydrocarbon fuels in Homogeneous Charge Compression Ignition engines. The fuel used in this study was simulated biogas which contained 67% CH4 and 33% CO2 by volume. Investigations were made into HCCI feasibility using inlet heating alone, HCCI feasibility using inlet heating and addition of simulated reformed fuel, feasibility of H2 production using fuel reforming and a full closed loop test including on-line H2 production. All HCCI results were compared to spark ignition baseline results. HCCI combustion for biogas shows significant improvement in NOx emissions and efficiency over SI combustion. However, it is difficult to achieve with biogas and was only stable with both reformed fuel addition and intensive inlet heating.

18

Preliminary investigations of the HCCI combustion system in a single cylinder research engine

60%

Motyl K. , Lisowski A.

Journal of KONES

|

2007

|

tom Vol. 14, No. 3

429-436

EN

This paper describes the results of the preliminary experimental research of the HCCI combustion system in a single cylinder research engine fuelled by means of natural gas containing 95% methane. In this research, influence of the initial temperature of the charge and mixture composition on the maximum combustion pressure, maximum speed of pressure growth, selfignition delay time, combustion time, maximum combustion temperature, heat release and combustion efficiency have been studied. The paper contains: description of the engine modification to adopt it for HCCI operation requirements, applied measurements equipment, selected results of the experimental research. The results shows that initial charge temperature and mixture composition (relative air/fuel ratio coefficient) have essential influence on the engine operating results. The experimental research has been conducted for the varied initial charge temperature from 140 centigrade up to 210 centigrade and for varied relative air/fuel ratio coefficient 1=1; 1=1.5; 1=1.7; 1=2. Maximum charge pressure, maximum speed of pressure growth selfignition delay time was rather unaffected on the initial charge temperature increase beyond 200 centigrade. Previous and current author's research works have indicated that extremely low emissions and high combustion efficiencies are possible to reach if homogeneous charge compression ignition is applied.

19

Numerical investigation into the effect of direct fuel injection on thermal stratification in HCCI engine

57%

Gęca M. , Hunicz J. , Jaworski P.

Combustion Engines

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2017

|

tom R. 56, nr 2

137--140

EN

Despite the fact that HCCI engines are distinguished by mixture homogeneity, some degree of stratification always appears inside a combustion chamber. It is especially applied to residual effect engines utilizing negative valve overlap. Mixture stratification is a result of the imperfect mixing of fresh air with trapped residuals. Direct fuel injection introduces stratification as well, due to fuel vaporization. As a consequence, the temperature within the combustion chamber is uneven. Thermal stratification affects auto-ignition timing and combustion evolution in a high extent. The purpose of this study was to evaluate a degree of thermal stratification in HCCI engine utilizing negative valve overlap. Investigations were performed using three-dimensional CFD model of the combustion system, made by using AVL FIRE software. Simulations were realized for various timings of fuel injection into the cylinder. It was found that fuel injection timing had a significant effect on the thermal stratification and resulting auto-ignition timing.

20

Hydrocarbon species in SI and HCCI engine using winter grade commercial gasoline

57%

Elghawi U. , Mayouf A. , Tsolakis A.

Combustion Engines

|

2020

|

tom R. 59, nr 1

17--24

EN

The study provides a qualitative and quantitative analysis of the C5-C11 hydrocarbon species generated in Spark Ignition - Homogeneous Charge Compression Ignition (SI/HCCI) gasoline direct injection (GDI) engine at range of operating conditions. The presented results and data were obtained from the combustion of winter grade commercial gasoline containing 2% w/w ethanol (C2H5OH) for the engine operated in steady-state, fully warmed-up condition. The hydrocarbon analysis in exhaust gases was executed on a Gas Chromatography-Mass Spectrometer (GC-MS) apparatus directly connected to the engine exhaust via heated line. The highest concentration of the total hydrocarbon emissions was obtained under low load HCCI engine operation at stoichiometric fuel-air ratio. The major hydrocarbon compounds detected in the collected samples were benzene, toluene, p-xylene, and naphthalene. Benzene originates from the incomplete combustion of toluene and other alkylbenzenes which are of considerable environmental interest. During the SI engine operation, increase of the engine speed and load resulted in the increase of benzene and the total olefinic species with simultaneous decrease in isopentane and isooctane. The same trends are seen with the engine operating under HCCI mode, but since the combustion temperature is always lower than SI mode under the same engine conditions, the oxidation of fuel paraffin in the former case was less. As a result, the total olefins and benzene levels in HCCI mode were lower than the corresponding amount observed in SI mode. Aromatic compounds (e.g., toluene), except for benzene, were produced at lower levels in the exhaust when the engine speed and load for both modes were increased.