Study on homogeneous charge compression ignition combustion in argon circulated closed cycle hydrogen engine

It is important to improve thermal efficiency and to reduce harmful exhaust gas emissions in internal combustion engines. A closed cycle engine system that uses a monatomic molecular gas as the working fluid can be expected to have high thermal efficiency due to the high specific heat ratio of the gas. Several studies have been reported on closed cycle engines with conventional spark ignition or compression ignition. This research newly proposes an argon circulated closed cycle homogeneous charge compression ignition (HCCI) engine system fueled with hydrogen. In this engine system, effects of in-cylinder gas initial temperature and residual water in recirculated gas on combustion characteristics were investigated. The results show that the system with argon circulation has the wider range of operable conditions and the higher thermal efficiency compared to the case with air as the working fluid.     

Effects of compression ratio on the combustion characteristics of a homogeneous charge compression ignition engine

The effects of homogeneous charge compression ignition (HCCI) engine compression ratio on its combustion characteristics were studied experimentally on a modified TY1100 single cylinder engine fueled with dimethyl ether. The results show that dimethyl ether (DME) HCCI engine can work stably and can realize zero nitrogen oxides (NO_x) emission and smokeless combustion under the compression ratio of both 10.7 and 14. The combustion process has obvious two stage combustion characteristics at ɛ = 10.7 (ɛ refers to compression ratio), and the combustion beginning point is decided by the compression temperature, which varies very little with the engine load; the combustion beginning point is closely related to the engine load (concentration of mixture) with the increase in the compression temperature, and it moves forward versus crank angle with the increase in the engine load at ɛ = 14; the combustion durations are shortened with the increase in the engine load under both compression ratios. __________ Translated from Chinese Journal Combustion Engine Engineering, 2006, 27(4): 9–12 [译自: 内燃机工程]     

Multi-dimensional modeling of the application of catalytic combustion to homogeneous charge compression ignition engine

The detailed surface reaction mechanism of methane on rhodium catalyst was analyzed.Comparisons betweennumerical simulation and experiments showed a basic agreement.The combustion process of homogeneouscharge compression ignition(HCCI)engine whose piston surface has been coated with catalyst(rhodium andplatinum)was numerically investigated.A multi-dimensional model with detailed chemical kinetics was built.The effects of catalytic combustion on the ignition timing,the temperature and CO concentration fields,and HC,CO and NO_x emissions of the HCCI engine were discussed.The results showed the ignition timing of the HCCIengine was advanced and the emissions of HC and CO were decreased by the catalysis.     

Experimental study of combustion and emission characteristics of ethanol fuelled port injected homogeneous charge compression ignition (HCCI) combustion engine

The homogeneous charge compression ignition (HCCI) is an alternative combustion concept for in reciprocating engines. The HCCI combustion engine offers significant benefits in terms of its high efficiency and ultra low emissions. In this investigation, port injection technique is used for preparing homogeneous charge. The combustion and emission characteristics of a HCCI engine fuelled with ethanol were investigated on a modified two-cylinder, four-stroke engine. The experiment is conducted with varying intake air temperature (120–150 °C) and at different air–fuel ratios, for which stable HCCI combustion is achieved. In-cylinder pressure, heat release analysis and exhaust emission measurements were employed for combustion diagnostics. In this study, effect of intake air temperature on combustion parameters, thermal efficiency, combustion efficiency and emissions in HCCI combustion engine is analyzed and discussed in detail. The experimental results indicate that the air–fuel ratio and intake air temperature have significant effect on the maximum in-cylinder pressure and its position, gas exchange efficiency, thermal efficiency, combustion efficiency, maximum rate of pressure rise and the heat release rate. Results show that for all stable operation points, NO_x emissions are lower than 10 ppm however HC and CO emissions are higher.     

Experimental investigations on a hydrogen diesel homogeneous charge compression ignition engine with exhaust gas recirculation

In this experimental study, hydrogen was inducted along with air and diesel was injected into the cylinder using a high pressure common rail system, in a single cylinder homogeneous charge compression ignition engine. An electronic controller was used to set the required injection timing of diesel for best thermal efficiency. The influences of hydrogen to diesel energy ratio, output of the engine and exhaust gas recirculation (EGR) on performance, emissions and combustion were studied in detail. An increase in the amount of hydrogen improved the thermal efficiency by retarding the combustion process. It also lowered the exhaust emissions. Large amounts of hydrogen and EGR were needed at high outputs for suppressing knock. The range of operation was brake mean effective pressures of 2–4 bar. The levels of HC and CO emitted were not significantly influenced by the amount of hydrogen that was used.     

Homogeneous charge compression ignition (HCCI) combustion of diesel fuel with external mixture formation

HCCI (Homogeneous Charge Compression Ignition) has been touted for many years as the alternate technology of choice for future engines, preserving the inherent efficiency of CIDI (Compression Ignition Direct Injection) engines while significantly reducing emissions. The current direction for all published diesel HCCI research is mixture preparation using the direct injection – system, referred to as internal mixture formation. The benefit of internal mixture formation is that it utilizes an already available direct injection system. Direct injected diesel HCCI can be divided into two areas, early injection (early in the compression stroke) and late injection (usually after Top Dead Center (aTDC)). Early direct injection HCCI requires carefully designed fuel injector to minimize the fuel wall-wetting that can cause combustion inefficiency and oil dilution. Late direct injection HCCI requires a long ignition delay and rapid mixing rate to achieve the homogeneous mixture. The ignition delay is extended by retarding the injection timing and rapid mixing rate was achieved by combining high swirl with toroidal combustion-bowl geometry. There is a compromise between Direct Injection (DI) and HCCI combustion regimes. Even under ideal conditions, it can prove difficult to form a truly homogeneous charge, which leads to elevated emissions when compared to true homogenous charge combustion and also strongly contribute to the high sensitivity of the combustion phasing to external parameters. The alternative to the internal mixture formation is, predictably, external mixture formation. By introducing the fuel external to the combustion chamber one can use the turbulence intake process to create a homogeneous charge regardless of engine conditions. This eliminates the need for combustion system changes which were necessary for the internal mixture formation method. With this method, the combustion system remains fully optimized for direct injection and also capable of running in HCCI combustion mode with nearly ideal mixture preparation. The key to the external mixture formation with diesel fuel is proper mixture preparation.     

Application of exhaust gas fuel reforming in diesel and homogeneous charge compression ignition (HCCI) engines fuelled with biofuels

This paper documents the application of exhaust gas fuel reforming of two alternative fuels, biodiesel and bioethanol, in internal combustion engines. The exhaust gas fuel reforming process is a method of on-board production of hydrogen-rich gas by catalytic reaction of fuel and engine exhaust gas. The benefits of exhaust gas fuel reforming have been demonstrated by adding simulated reformed gas to a diesel engine fuelled by a mixture of 50% ultra low sulphur diesel (ULSD) and 50% rapeseed methyl ester (RME) as well as to a homogeneous charge compression ignition (HCCI) engine fuelled by bioethanol. In the case of the biodiesel fuelled engine, a reduction of NO_x emissions was achieved without considerable smoke increase. In the case of the bioethanol fuelled HCCI engine, the engine tolerance to exhaust gas recirculation (EGR) was extended and hence the typically high pressure rise rates of HCCI engines, associated with intense combustion noise, were reduced.     

Control of homogeneous charge compression ignition combustion in a two-cylinder gasoline direct injection engine with negative valve overlap

Homogeneous charge compression ignition (HCCI) has challenges in ignition timing control, combustion rate control, and operating range extension. In this paper, HCCI combustion was studied in a two-cylinder gasoline direct injection (GDI) engine with negative valve overlap (NVO). A two-stage gasoline direct injection strategy combined with negative valve overlap was used to control mixture formation and combustion. The gasoline engine could be operated in HCCI combustion mode at a speed range of 800–2 200 r/min and load, indicated mean effective pressure (IMEP) range of 0.1–0.53 MPa. The engine fuel consumption is below 240 g/(kW⁻¹·h⁻¹), and the NO _x emission is below 4 × 10⁻⁵ without soot emission. The effect of different injection strategies on HCCI combustion was studied. The experimental results indicated that the coefficient of variation of the engine cycle decreased by using NVO with two-stage direct injection; the ignition timing and combustion rate could be controlled; and the operational range of HCCI combustion could be extended. Translated from J Tsinghua Univ (Sci & Tech), 2006, 46(5): 720–723 [译自: 清华大学学报]     

A new heat release rate (HRR) law for homogeneous charge compression ignition (HCCI) combustion mode

Homogeneous charge compression ignition (HCCI) engines are drawing attracting attention as the next-generation’s internal combustion engine, mainly because of its very low NO_x and soot emissions and also for improvement in engine efficiency. Much research has been carried out in order to go deeper in this combustion process using multizone models or CFD codes. These simulation tools, although they can give a detailed view of the combustion process, are very time consuming and the results depend a lot on the initial conditions. A previous step to be considered in the simulation of the HCCI process is a heat release law evaluated from results of the experiment and a zero-dimensional model. This paper focuses on the development of a new heat release rate (HRR) law that models the HCCI process when the combustion chamber is considered as a homogeneous volume. The parameters of this law have been adjusted through an optimization process that has allowed to fit the combustion chamber pressure. All the engine operative conditions from low to full load have been successfully simulated with this HRR law, with the maximum error in the estimation of combustion chamber pressure less than 2%.     

Exergy analysis of diesel/biodiesel combustion in a homogenous charge compression ignition (HCCI) engine using three-dimensional model

Exergy analysis gives the presentation of a system relative to its best performance. In addition, the exergy destructed can react with its surrounding and harm environment processes. This study investigated the effect of biodiesel fuel blended with diesel fuel (i.e. 0%, 20%, and 50% blending of biodiesel fuel with conventional diesel fuel) on various exergy terms in an HCCI engine. To model the energy balance a 3-D CFD code was utilized. Using energy and combustion analyses results, the researchers calculated various exergy terms by developing a FORTRAN based code. To ensure the integrity of modeling, the results of the in-cylinder pressure and heat release rate were compared with the experimental results for pure diesel fuel. This comparison indicated a good agreement between the two. With crank position at three fuel compositions, different rates of exergy and cumulative exergy terms were identified and calculated separately. With the increase in the biodiesel volume percentage from 0% to 20% and 50%, exergy efficiency increased by 4.9% and 5.7%. Also, the cumulative heat loss exergy decreased by 4.4% and 9.7%, respectively.     

Experimental study and chemical analysis of n-heptane homogeneous charge compression ignition combustion with port injection of reaction inhibitors

The control of ignition timing in the homogeneous charge compression ignition (HCCI) of n-heptane by port injection of reaction inhibitors was studied in a single-cylinder engine. Four suppression additives, methanol, ethanol, isopropanol, and methyl tert-butyl ether (MTBE), were used in the experiments. The effectiveness of inhibition of HCCI combustion with various additives was compared under the same equivalence ratio of total fuel and partial equivalence ratio of n-heptane. The experimental results show that the suppression effectiveness increases in the order MTBE < isopropanol ? ethanol < methanol. But ethanol is the best additive when the operating ranges, indicated thermal efficiency, and emissions are considered. For ethanol/n-heptane HCCI combustion, partial combustion may be observed when the mole ratio of ethanol to that of total fuel is larger than 0.20; misfires occur when the mole ratio of ethanol to that of total fuel larger than 0.25. Moreover, CO emissions strongly depend on the maximum combustion temperature, while HC emissions are mainly dominated by the mole ratio of ethanol to that of total fuel. To obtain chemical mechanistic informations relevant to the ignition behavior, detailed chemical kinetic analysis was conducted. The simulated results also confirmed the retarding of the ignition timing by ethanol addition. In addition, it can be found from the simulation that HCHO, CO, and C₂H₅OH could not be oxidized completely and are maintained at high levels if the partial combustion or misfire occurs (for example, for leaner fuel/air mixture).     

Modeling study on the production of hydrogen/syngas via partial oxidation using a homogeneous charge compression ignition engine fueled with natural gas

The production of hydrogen and syngas from natural gas using a homogeneous charge compression ignition reforming engine is investigated numerically. The simulation tool used was CHEMKIN 3.7, using the GRI-3 natural gas combustion mechanism. This simulation was conducted on the changes in hydrogen and syngas concentration according to the variations of equivalence ratio, intake temperature, oxygen enrichment, engine speed, initial pressure, and fuel additives with partial oxidation combustion. The simulation results indicate that the hydrogen/syngas yields are strongly dependent on the equivalence ratio with maxima occurring at an optimal equivalence ratio varying with engine speed. The hydrogen/syngas yields increase with increasing intake temperature and oxygen contents in air. The hydrogen/syngas yields also increase with increasing initial pressure, especially at lower temperatures, yet high temperature can suppress the pressure effect. Furthermore, it was found that the hydrogen/syngas yields increase when using fuel additives, especially hydrogen peroxide. Through the parametric screening studies, optimum operating conditions for natural gas partial oxidation reforming are recommended at 3.0 equivalence ratio, 530 K intake temperature, 0.3 oxygen enrichment, 500 rpm engine speed, 1 atm initial pressure, and 7.5% hydrogen peroxide.     

Optimization of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine hybrid system for distributed power generation

In a previous study, a new hybrid system of molten carbonate fuel cell (MCFC) and homogeneous charge compression ignition (HCCI) engine was developed, where the HCCI engine replaces the catalytic burner and produces additional power by using the left-over heating values from the fuel cell stack. In the present study, to reduce the additional cost and footprint of the engine system in a hybrid configuration, the possibility of engine downsizing is investigated by using two strategies, i.e. the use of a turbocharger and the use of high geometric compression ratio for the engine design, both of which are to increase the density of the intake charge and thus the volumetric efficiency of the engine. Combining these two strategies, we suggest a new engine design with ∼60% of displacement volume of the original engine. In addition, operating strategies are developed to run the new hybrid system under part load conditions. It is successfully demonstrated that the system can operate down to 65% of the power level of the design point, while the system efficiency remains almost unchanged near 63%.     

Experimental investigation of tetrahydrofuran combustion in homogeneous charge compression ignition (HCCI) engine: Effects of excess air coefficient,engine speed and inlet air temperature

In this study, the effects of tetrahydrofuran (THF) which is nontoxic and generated from renewable environmentally friendly lignocelluloses, and n-heptane/THF blends on combustion, performance and emission characteristics were investigated at various lambda, engine speed and inlet air temperatures. Wide ranges of lambda value and engine speed were investigated and the results were presented in comparison to n-heptane as reference fuel. The combustion parameters such as cylinder pressure, heat release rate, in-cylinder gas temperature, CA10, CA50, thermal efficiency, ringing intensity, maximum pressure rise rate and imep, the performance parameters such as brake torque, power output, specific fuel consumption and HC and CO emissions were determined. Operating range of the HCCI engine was also determined. The results showed that, increasing the lambda value decreased both the in-cylinder pressure and the heat release rate for all test fuels. The addition of tetrahydrofuran led to retard combustion phasing. Thermal efficiency increased about 54% for F60N40 compared to n-heptane at 60 °C inlet air temperature, 1200 rpm engine speed and λ = 2.2. The results also showed that HC and CO emissions increased with the increase of tetrahydrofuran. Furthermore, tetrahydrofuran caused to expand HCCI operating range towards to knocking and misfiring boundaries.     

Experimental study of the performances of a modified diesel engine operating in homogeneous charge compression ignition (HCCI) combustion mode versus the original diesel combustion mode

Homogeneous charge compression ignition (HCCI) combustion mode provides very low NO_x and soot emissions; however, it has some challenges associated with hydrocarbon (HC) emissions, fuel consumption, difficult control of start of ignition and bad behaviour to high loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NO_x production in diesel and HCCI combustion mode. However EGR has different effects on combustion and emissions, which are difficult to distinguish. This work is intended to characterize an engine that has been modified from the base diesel engine (FL1 906 DEUTZ-DITER) to work in HCCI combustion mode. It shows the experimental results for the modified diesel engine in HCCI combustion mode fueled with commercial diesel fuel compared to the diesel engine mode. An experimental installation, in conjunction with systematic tests to determine the optimum crank angle of fuel injection, has been used to measure the evolution of the cylinder pressure and to get an estimate of the heat release rate from a single-zone numerical model. From these the angle of start of combustion has been obtained. The performances and emissions of HC, CO and the huge reduction of NO_x and smoke emissions of the engine are presented. These results have allowed a deeper analysis of the effects of external EGR on the HCCI operation mode, on some engine design parameters and also on NO_x emission reduction.     

Synthesized evaluation of various injection regimens on hydrogen propelled homogeneous charge compression ignition and dual fuel modes for an automotive application

The present work aimed to perform a comparative study between the hydrogen diesel homogeneous charge compression ignition (HDHCCI) and hydrogen diesel dual fuel (HDDF) modes with multiple injection regimens. The results showed that the maximum feasible hydrogen energy shares (HES) were 73.99% and 27.46% for the HDDF and HDHCCI modes in a single pulse injection. The level of efficiency increased while increasing HES in the HDHCCI mode for any injection regimen. Conversely, the level of efficiency decreased on increasing HES for the HDDF mode, however it yields higher efficiency than the HDHCCI mode at a steady HES operation. The extremely low NO emission was attained using single pulse and twin pulse HDHCCI modes as compared with HDDF mode, and vice versa for smoke and HC emissions, since the existence of cool flame due to too early injection timings drastically altered the combustion characteristics of HDHCCI mode.     

Influence of hydrogen co-combustion with diesel fuel on performance,smoke and combustion phases in the compression ignition engine

The main objective of this study was to examine impact of hydrogen addition to the compression ignition engine fueled with either rapeseed methyl ester (RME) or 7% RME blended diesel fuel (RME7) on combustion phases and ignition delay as well as smoke and exhaust toxic emissions. Literature review shows in general, hydrogen in those cases is used in small amounts below lower flammability limits. Novelty of this work is in applying hydrogen at amounts up to 44% by energy as secondary fuel to the compression ignition engine. Results from experiments show that increase of hydrogen into the engine makes ignition delay shortened that also affects main combustion phase. In all tests the trends of exhaust HC and CO toxic emissions vs. hydrogen addition were negative. The trend of smokiness decreased steadily with increase of hydrogen. Amounts of hydrogen addition by energy share were limited to nearly 35% due to combustion knock occurring at nominal load.     

Role of hydrogen in improving performance and emission characteristics of homogeneous charge compression ignition engine fueled with graphite oxide nanoparticle-added microalgae biodiesel/diesel blends

The development of low-temperature combustion models combined with the use of biofuels has been considered as an efficient strategy to reduce pollutant emissions like CO, HC. NO_x, and smoke. Indeed, Homogeneous Charge Compression Ignition (HCCI) is the new approach to drastically minimize NO_x emissions and smoke owing to the lower cylinder temperature and a higher rate of homogeneous A/F mixture as compared to compression ignition (CI) engines. The present research deal with the behavior analysis of a CI engine powered by diesel, Euglena Sanguinea (ES), and their blends (ES20D80, ES40D60, ES60D40, ES80D20). The experimental results revealed the highest brake thermal efficiency for ES20D80 although it decreased by 4.1% compared to diesel at normal mode. The average drop in HC, CO, and smoke was 2.1, 2.3, and 5.7% for ES20D80 as opposed to diesel fuel. Therefore, in the next stage, ES20D80 with various concentrations of graphite oxide (GO) nanoparticle (20, 40, 60, and 80 ppm) was chosen to carry out experiments in the HCCI mode, in which hydrogen gas was induced along with air through the intake pipe at a fixed flow rate of 3 lpm for the enrichment of the air-fuel mixture. As a result, the combination of hydrogen-enriched gas and GO-added ES20D80 in the HCCI mode showed similar performance to the CI engine but registered a major reduction of NO_x and smoke emissions, corresponding to 75.24% and 53.07% respectively, as compared to diesel fuel at normal mode.     

Hydrogen and propane implications for reactivity controlled compression ignition combustion engine running on landfill gas and diesel fuel

A detailed investigation of employing landfill gas together with additives such as hydrogen or propane or both as a primary low reactivity fuel in a reactivity controlled compression ignition combustion of a diesel engine is conducted. A 3401E caterpillar single-cylinder diesel engine with a bathtub piston bowl profile is utilized to execute the study. The engine is operated at various intake pressures of 1.6, 1.9, and 2.2 bar, and runs at a fixed engine speed of 1300 rpm. For verification purposes, the conduct of the present engine running on pure methane as a low reactivity fuel is compared to that of the same engine available in the literature. Next, a numerical simulation is made to assess the performance of the present engine running on landfill gas plus the additives. Based on the obtained results, injecting either hydrogen or propane or a combination of both up to a total amount of 10% by volume to the premixed of landfill gas and air, and advancing diesel fuel injection timing of about 20–30 deg. crank angle, render the landfill gas utilization quite competitive with using methane alone. Applying an enriched landfill gas in a reactivity controlled compression ignition diesel engine, as a power generator, drastically reduces the greenhouse gas emission to the atmosphere. Also, the CO and UHC mole fraction in the exhaust gas can be eliminated by either advancing the start of diesel injection or using hydrogen or propane or both as additives. In addition, utilizing hydrogen or propane or a combination of both with the primary fuel improves the peak pressure to about 16% in comparison with that of landfill gas alone.     

The peculiar influence of the mineral impurities content in coal-water fuel on the regularities of fuel drop ignition and combustion

This paper presents the results of the comparative research of combustion specifics of coal-water fuel produced from low-ash and high-ash Ukrainian flame coal. The analysis shows that the effect of the ash content in the coal-water fuel on the duration of the burning of a fuel drop depends on the drop size. The full combustion time of CWF drop based on the low-ash coal can be both less and longer than that of high-ash coal under the identical conditions for different equivalent diameters of the fuel drop. This specific is explained with the domination of different physical factors during the fuel combustion process.The results of this research extend significantly our knowledge of coal-water fuel, allow understanding some issues of its combustion and are important for the design of the specialized energy facility which is used coal-water fuel as an energy source.