Direct Injection Strategy Research Articles

Experimental investigation on the combustion and emissions in a pilot ignited direct injection natural gas engine using HCDI strategy

Pilot ignited direct injection natural gas engines have been increasingly attractive owing to their advantages in thermal efficiency and emissions. For conventional pilot ignited direct injection natural gas engines, soot emissions have been considered as an urgent issue, which could be possibly resolved by the adoption of homogenous charge direct injection strategy. To prove this viewpoint, this paper experimentally studied the effects of homogenous charge direct injection strategy on the combustion, emissions, thermal efficiency and operation stability of a pilot ignited direct natural gas engine. The results indicated that at low load, the application of homogenous charge direct injection strategies has negative effects on NOx, CO and HC emissions; though soot emissions could be improved, the negative effects seem to be more predominant. At high load, though NOx and HC emissions are impaired with the application of homogenous charge direct injection strategies, CO and soot emissions could be substantially improved with optimized injection parameters. Thermal efficiency could be slightly improved at low load condition and could be greatly raised at high load condition. Additionally, the adoption of homogenous charge direct injection strategies would increase the instabilities of engine operation, however, this behavior is more significant at low load condition.

Experimental study on the interaction between flame propagation and wall film in a confined vessel

With applying the direct injection strategy, it is inevitable to develop a liquid fuel wall film, which would significantly affect the combustion process afterward. In this work, the interactions between the premixed flame propagation and wall film in a confined vessel were investigated thoroughly. The methane-air premixed mixture was used to generate the flame, while the wall films were prepared by directly placing liquid fuel onto a plate surface that attached inside of the combustion chamber. Besides laminar flame, a turbulent premixed flame was also induced by putting a cluster of columnar obstacles on the path of the flame propagation to study the effects of turbulent flame on film consumption. The flame propagation processes, as well as the pressure variations, were captured and recorded by a high-speed Schlieren photographic system and a pressure transducer, respectively. The flame morphology, propagation speed, and pressure characteristics were compared to each other under dry and film walls by varying initial conditions. The impact of different types of wall films and chamber structures (e.g., with and without narrow channels of different widths) on the flame propagation was also examined. Results indicated that the flame propagation process was accelerated because the high reactivity species within the film get vaporized and well mixed into the methane-air combustion mixture. Under turbulent combustion conditions, the vaporization and loss of the film were enhanced by the strong heat transfer as indicated by the Schlieren images observations. Furthermore, different fuel/oil films have different mass loss rates under combustion conditions due to the vaporization property. N-dodecane fuel film has the highest film loss rate, followed by diesel and lube oil film. In addition, the turbulent flame leads to higher film loss as well by increasing the heat transfer.

Homogeneous Charge with Direct Injection Strategy to Achieve High Efficiency and Clean Combustion in Diesel Engines

Homogeneous Charge with Direct Injection Strategy to Achieve High Efficiency and Clean Combustion in Diesel Engines

Numerical investigation of the effect of fuel concentration stratification on gasoline compression ignition combustion under low-to-medium load conditions

In the present study, a numerical investigation of the effect of fuel concentration stratification on engine performance for the combined port- and direct-injection (PIDI) strategy and two direct-injection (2DI) strategy under low-to-medium load conditions was performed by coupling the KIVA-3V code with the genetic algorithm. In addition, the sensitivity of operating parameters on combustion characteristics for different injection strategies was also explored. The results indicated that the PIDI strategy could achieve much better fuel economy and lower combustion noise while with a stronger trade-off relationship between them compared to the 2DI strategy. At low loads, the required initial temperature and EGR rate for the optimal cases of the PIDI strategy are overall lower than those of the 2DI strategy. Moreover, the ranges of the required initial pressure and injection pressure for the PIDI strategy are wider than those of the 2DI strategy. As load increases, the effects of different injection strategies on the optimal cases are weakened. For both strategies, initial temperature plays a dominant role in determining the combustion phasing and engine performance. However, the effects of injection parameters, i.e., injection timing, pilot fraction (2DI strategy) and premixed ratio (PIDI strategy), are dependent on the load. In addition, compared to the 2DI strategy, the combustion phasing, fuel economy and combustion noise of the PIDI strategy show more dependence on the initial temperature, while the NOx emissions are less sensitive to the initial temperature.

Feasibility study of the combustion strategy of n-butanol/diesel dual direct injection (DI2) in a compression-ignition engine

For n-butanol/diesel dual-fuel combustion, there are two different implementations, i.e., dual direct injection (DI2) strategy and reactivity controlled compression ignition (RCCI) strategy. The DI2 strategy is a novel combustion concept, which is expected to address the inefficient combustion and high pressure rise rate dilemmas raised by RCCI. In this work, the full-parameter optimizations of DI2 and RCCI were first performed at mid load, and the optimal cases were comprehensively compared. The potential benefits of DI2 over RCCI and its optimal operating parameters were determined. The results indicate that DI2 can achieve low nitrogen oxides (NOx) emissions below 0.00094 g/kWh and near-zero soot emissions while keeping high fuel economy near 167 g/kWh comparable to that of RCCI, but it usually yields higher NOx, soot, and carbon dioxide (CO2) emissions than RCCI. In the optimal DI2 cases, very advanced n-butanol injection timing (before −120°CA ATDC), high n-butanol energy fraction (around 0.94), and early diesel injection timing (near −50 °CA ATDC) are adopted. Meanwhile, the combination of a narrow n-butanol spray angle (30°<αbutanol < 50°) and a wide diesel spray angle (>65°) is preferred for DI2. Compared with RCCI, DI2 exhibits lower combustion losses, however, it suffers from higher exhaust and heat transfer losses. The higher intake temperature, exhaust gas recirculation (EGR) rate, and lower intake pressure are more beneficial for DI2. Moreover, it is suggested that DI2 is easier to achieve lower ringing intensity (RI), and the ignition timing and RI of DI2 are more sensitive to the n-butanol fraction than RCCI.

Experimental investigation of reactivity controlled compression ignition with n-butanol/n-heptane in a heavy-duty diesel engine

Butanol is a potential alternative fuel to be applied in the internal combustion engine for its sustainability and low-sooting propensity. In this paper, n-butanol is port injected as low reactivity fuel and n-heptane is directly injected into cylinder as high reactivity fuel to achieve high thermal efficiency as well as low soot/NOx emissions. To understand the effects of charge preparation parameters and load range of this reactivity controlled compression ignition combustion, experiments are performed in a single cylinder heavy-duty diesel engine. The results show that single direct injection causes either too early combustion phasing or excessive HC/CO emissions. Increasing the inlet boosting pressure is beneficial to obtain high thermal efficiency but HC/CO emissions deteriorate remarkably. The double direct injection strategy can phase the combustion properly and obtain high gross indicated efficiency without sacrificing CO emissions too much. Additionally, a high exhaust gas recirculation rate is necessary to achieve proper control of combustion phasing as the reactivity of n-butanol is not low enough. It is found that the n-butanol/n-heptane reactivity controlled compression ignition can be operated from low to medium loads. And the sensitivity of combustion phasing to the direct injection timing decreases as the load increases. At medium–high load, combustion couldn't be phased after the top dead center, which leads to high pressure rise rates and high peak pressures. Extremely low particulate matter and NOx emissions are observed throughout this tested load range and a gross indicated efficiency over 50% can be observed from low to medium load.

An experimental study of the injection strategies on engine performance of the butanol/biodiesel dual-fuel Intelligent Charge Compression Ignition mode

Intelligent Charge Compression Ignition (ICCI) combustion mode is a novel dual-fuel combustion strategy that has been proposed recently. In ICCI combustion mode, two fuels with different reactivity are directly injected during the intake stroke and compression stroke, respectively, to achieve flexible reactivity gradient and equivalence ratio stratification. In this study, experiments were conducted on a single-cylinder diesel engine to investigate the effects of butanol direct injection strategies on the engine running with ICCI combustion mode at a constant speed of 1500 r/min and medium load. Results showed that ICCI combustion mode was composed of premixed heat release and diffusion heat release. In compare, the percentage of premixed heat release was higher than the diffusion heat release. With fixed biodiesel direct injection timing (SOI2), retarding butanol single injection timing (SOI1) would delay combustion phasing while not distinctively affect ignition timing. SOI1 showed significant effect on the thermal efficiency and engine emissions. Indicated thermal efficiency (ITE) decreased at first and then slightly increased with retarding of SOI1, while the nitrogen oxides (NOx) emissions were always at low levels. As the butanol second direct injection timing (SOI1-2) retard and the corresponding energy ratio increase, more butanol entered into the crevice/squish regions, leading to the increase of unburned hydrocarbon (HC) and carbon monoxide (CO) emissions. EGR strategy helps to significantly reduce NOx emissions without affecting ITE although penalized HC and CO emissions are resulted in. The optimum butanol direct injection strategies were butanol single direct injection, especially in the early SOI1, in which the thermal efficiency was higher and emissions were at very low levels (NOx &lt; 0.4 g/kW h).

Gaseous jet through an outward opening injector: Details of mixing characteristic and turbulence scales

Direct injection (DI) strategy of natural gas (NG) into internal combustion engines (ICE) has led to higher thermal efficiency and lower exhaust emissions. In order to thoroughly understand the most relevant phenomena affecting the performances of such engines, computational fluid dynamics (CFD) plays a key role as an accurate description of the jet evolution and interaction within the combustion chamber is required to that aim.Accurate description of high-pressure gaseous jets is rather challenging at high Mach numbers, as the injected gas is strongly under-expanded once in the ambient, giving room to shocks due to compressibility effects. Also the interaction between shock waves and mixing layers needs to be carefully represented with a multi-dimensional model, calling for substantial computational resources requirements.In this paper a numerical investigation of the behavior of a gaseous jet (Argon) through an outward opening injector has been carried out. A Large Eddy Simulation (LES) approach has been used in order to track the structures derived by the interaction of the injected fuel with the surrounding ambient. Although already good results were obtained using a Reynolds Averaged Navier-Stokes (RANS) approach, the adoption of LES is required to characterize more accurately the jet properties in terms of vortex structures and mixing effectiveness. The effect of the Nozzle Pressure Ratio (NPR) on the jet evolution has been highlighted in the paper, showing how a higher NPR would give a faster injection process, compromising however the homogeneity of the mixture.

Dual fuel intelligent charge compression ignition (ICCI) combustion: Efficient and clean combustion technology for compression ignition engines

A brand-new combustion mode intelligent charge compression ignition (ICCI) was proposed to be expected for ultra-high efficiency and low emissions simultaneously. The introduce for conceptual model of ICCI mode aimed to realize flexible and controllable in-cylinder charge stratification fed by two complementary fuel, gasoline and diesel. To fulfill this unique dual-fuel combustion mode, two common-rail direct-injection systems were independently utilized on a modified single-cylinder engine, controlled by their own on-limits electronic control unit, respectively. Fundamentally experimental investigations on ICCI mode was conducted by the fuel ratio variation at 8 bar indicated mean effective pressure (IMEP). The experimental results showed that high indicated thermal efficiency close to 50% and low NOx emissions well below 0.12 g/kWh were simultaneously achieved at 85% gasoline ratio. Based on the optimal gasoline ratio, multi-injection strategies of ICCI mode can further improve thermal efficiency and emissions. Meanwhile, comparisons of ICCI with other combustion modes, including reactivity-controlled compression ignition (RCCI), G85 dual direct injection (DDI), G85, and G70 single direct injection (DI) strategies were carried out. In the similar operating conditions, ICCI combustion got better performance compared with other combustion modes, achieving about 2% increased indicated thermal efficiency in comparison to RCCI or DDI mode and near none NOx emissions compared with DI combustion. Prospectively, if it can be continually researched, ICCI has a large potential based on the further optimization in the future.

The Virtual Engine Development for Enhancing the Compression Ratio of DISI-Engines Combining Water Injection, Turbulence Increase and Miller Strategy

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;The increase in efficiency is the focus of current engine development by adopting different technologies. One limiting factor for the rise of SI-engine efficiency is the onset of knock, which can be mitigated by improving the combustion process. HCCI/SACI represent sophisticated combustion techniques that investigate the employment of pre-chamber with lean combustion, but the effective use of them in a wide range of the engine map, by fulfilling at the same time the need of fast load control are still limiting their adoption for series engine. For these reasons, the technologies for improving the characteristics of a standard combustion process are still largely investigated. Among these, water injection, in combination with the Miller cycle, offers the possibility to increase the knock resistance, which in turn enables the rise of the engine geometric compression ratio.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;The need for reducing measurements and executing specific tests are mandatory to make still the IC-Engines competitive to other powertrain solutions. The implementation of water injection can be realized through different engine layouts and injection strategies. Besides, the results of injecting water are strictly dependent on the base engine features and load point. Therefore, virtual development becomes essential to study many engine configurations.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;In this work, indirect and direct water injection strategies are considered to increase the engine knock limit. The investigation is conducted with the 3D-CFD-Tool QuickSim, which was developed at IVK/FKFS Stuttgart. The implementation of water physics, the extension of simulation domain up to full engine (including intake and exhaust system), and the possibility to analyze multiple cycles allow understanding the effects of water and valve timing on engine behavior. The simulation validation was accomplished through the experiments carried out on a single-cylinder engine, equipped with indirect and direct water injections. The set-up of a virtual test bench is exploited to increase the engine geometric compression ratio, by combining Miller valve timing strategies with water injection. Particularly the investigation of a water-optimized injector targeting and position for the direct water injector enables increasing the turbulence within the cylinder and compensating for the effect of early intake valve closure. With the support of a newly developed knock model, the effect of water and the modified valve overlap on the combustion process is analyzed, to increase engine efficiency and propose a new approach for future powertrain engine development process.&lt;/div&gt;&lt;/div&gt;

Effect of multiple fuel injection strategies on mixture formation and combustion in a hydrogen-fueled rotary range extender for battery electric vehicles

The hydrogen-fueled range extender based on the rotary engine is a promising solution for battery electric vehicles due to key advantages such as: high efficiency, small packaging dimensions and low weight within the framework of the near zero-emission concept. Although rotary engine has been examined over the past years, the detailed knowledge of hydrogen combustion in the rotary engine with direct injection system has not been investigated properly. In this paper, the rotary range extender was numerically studied with a focus on the influence of the direct multiple injection strategies on hydrogen distribution and combustion. The result demonstrates that due to large flame speed and diffusion length the engines fueled by pure hydrogen differ significantly from the engines with conventional fuel. The process is characterized by the weak influence of turbulence on the flame during almost the whole combustion stroke except for the late stages when 70% of the fuel is already burnt. Hence the difference in the injection strategies lead to different local hydrogen distribution that has effects on combustion rate and performance characteristics significantly. Fuel stratification leads to the formation of subregions with various hydrogen concentration. The lean mixture cannot provide enough high temperature, whereas the rich mixture is characterized by a lack of oxygen. The total NOx formation can be twice lower in comparison with premixed combustion at the same averaged equivalence ratio. The direct multiple injection strategy allows the use of a higher averaged equivalence ratio up to 0.8 which results in larger power density in combination with low NOx emission.

Understanding partial fuel stratification for low temperature gasoline combustion using large eddy simulations

The development of gasoline compression ignition engines operating in a low temperature combustion mode depends heavily on robust control of the heat release profile. Partial fuel stratification is an effective method for controlling the heat release by creating a stratified mixture prior to autoignition, which can be beneficial for operation across a wide load range. In this study, three-dimensional large eddy simulations were used to model a double direct injection strategy for which 80% of the fuel was injected during the intake stroke, and 20% of the fuel was injected at varying timing during the compression stroke. The simulations replicated a set of experiments performed at Sandia National Laboratories on a 1-L single-cylinder research engine using E10 gasoline (gasoline fuel containing 10% vol. ethanol). The objective of this study is to analyze the effects of the double direct injection strategy on the compositional and thermal stratification of the mixture, and understand the best use of this operating strategy. The modeling results indicated that by retarding the start of the second injection, the mixture stratification increases, which can be used to control the autoignition timing and the combustion phasing. Ignition and CA50 (crank angle of 50% mass fraction burned) are dictated by the mass concentration of the richest zones in the combustion chamber, as well as their location. The richer zones have the lowest temperatures before ignition primarily due to evaporative cooling from direct fuel injection. Overall, this study enhances the understanding of partial fuel stratification that can be used for controlling the heat release in gasoline compression ignition engines.

A Methodology for Studying the Relationship Between Heat Release Profile and Fuel Stratification in Advanced Compression Ignition Engines

Low temperature combustion strategies have demonstrated high thermal efficiency with low pollutant emissions, (e.g. oxides of nitrogen and particulate matter) resulting from reduced heat transfer losses and lean air-fuel mixtures. One such advanced compression ignition combustion strategy, Reactivity Controlled Compression Ignition (RCCI), has demonstrated improved control over the heat release event due to the introduction of in-cylinder stratification of equivalence ratio and chemical reactivity via direct injection of a high-reactivity fuel into a premixed low-reactivity fuel/air mixture. The nature of the RCCI strategy provides inherent fuel flexibility, however, the direct injection strategy must be tailored to the combination of premixed and direct injected fuel chemistry and engine operating conditions to optimize efficiency and emissions. In this work, a 0-D methodology for predicting the required fuel stratification for a desired heat release rate profile for kinetically controlled stratified-charge combustion strategies is proposed. The methodology, referred to as Fuel Stratification Analysis (FSA), was inspired by a similar approach which utilized ignition predictions calculated via a Livengood-Wu integral approach correlated with experimental heat release profiles to determine in-cylinder temperature stratification in homogeneous charge compression ignition (HCCI) combustion. The methodology proposed in this work expands upon this method to include strategies involving fuel stratification (such as RCCI). Reacting and non-reacting CFD simulations were performed with the KIVA3V release 2 code to validate the CFD. Reacting simulations were validated against published experimental HCCI and RCCI data, and non-reacting simulations were used to generate fuel distribution profiles to compare to the FSA results. The results of this validation showed that the FSA method was able to provide good overall agreement in the predicted fuel distribution compared to the actual fuel distributions from CFD simulations within the range of injection timings of interest in RCCI combustion (-140o to about -35o after top-dead-center). For later injection timings, FSA predictions are not able to capture the actual fuel distributions present at the start of combustion, likely due to a transition into a mixing dominated, as opposed to a kinetically dominated, combustion regime, thereby violating one or more inherent method assumptions.

Effect of direct injection dimethyl ether on the micro-flame ignited (MFI) hybrid combustion characteristics of an optical gasoline engine at ultra-lean conditions

Ultra-lean burn combustion can significantly improve the fuel economy of gasoline engines. However, poor combustion stability and slow combustion need to be solved. Therefore, micro-flame ignited (MFI) hybrid combustion, a concept that ultra-lean gasoline is burned with compression auto-ignition of direct injection (DI) dimethyl ether (DME) in the cylinder, was employed. The effect of single and double DI DME strategies on the combustion characteristics and flame structures was investigated in an optical gasoline engine at lambda 2.0. The results show that the heat release process in the case of single DI DME consists of oxidation reactions of DME (stage I) and hybrid combustion of DME and gasoline (stage II). In the case of double DI DME, there is gasoline auto-ignition (stage III) after stages I and II. The ignition timing delays with decreased heat released in stage I regardless of DI strategies. Indicated mean effective pressure can be enhanced and the cyclic variation is reduced in the double DI conditions. The flame brightness increases with increased heat release rate regardless of DI DME strategies. The decay rate of turbulent flame propagation speed in double DI conditions is slower than that in single DI conditions, which improves combustion stability.

Investigating the effect of spray included angle on thermally stratified compression ignition with wet ethanol using computational fluid dynamics

Computational fluid dynamics (CFD) modeling was used in this study to explore the effect of spray included angle in a diesel engine with a re-entrant bowl piston. Previously, it was shown that thermally stratified compression ignition (TSCI) has the ability to control the heat release rate and extend the upper load limit of advanced combustion compared to Homogenous Charge Compression Ignition. TSCI can be achieved using either the direct injection of water into a premixed mixture of air and fuel or using a split direct injection strategy of a water-fuel mixture. The current study focuses on the latter variation of TSCI using wet ethanol as the direct injected water-fuel mixture. The CFD model implemented in CONVERGE with SAGE detailed chemistry solver was first validated using experimental results collected on a single-cylinder research engine. Then, the model was used to simulate different spray included angles to explore the effect of spray included angle on the thermal and equivalence ratio stratification that develops in the cylinder.The spray included angle was varied from 60° to 150° and the results indicate that the broader spray included angles targeted the regions of the cylinder outside of the piston bowl while the narrower angles targeted mostly inside of the piston bowl. Since the charge inside the piston bowl is naturally hotter due to spatial differences in heat transfer losses and the natural thermal stratification that occurs, when the bowl region is targeted, the difference between the temperature inside and outside piston bowl reduces. However, when targeting the region outside of the piston bowl (i.e., the squish region), the natural and forced thermal stratifications work together and the temperature difference between the bowl and squish regions increases. This results in higher thermal stratification for the broader included angles, which results in better control over the heat release rates.

An experimental study on low temperature combustion in a light duty engine fueled with diesel/CNG and biodiesel/CNG

Low temperature combustion potentially can improve engine efficiency coupled with the benefits of low nitrogen oxides, and particulate matter emissions, and vice versa high unburned hydrocarbon and carbon oxide emissions through in-cylinder fuel reactions. In this survey, the experiments were carried out using a modified one-cylinder reactivity controlled compression ignition engine, dual-fueled diesel/compressed natural gas and biodiesel/CNG, to investigate the effects of direct injection strategies on the engine combustion efficiency and emission characteristics. Different ratios of biodiesel blends at different premixed ratios were applied to the dual-fuel engine. The results showed that the start of liquid fuel direct injection timing has a crucial role in the performance and emission characteristic of dual-fuel RCCI combustion. Advancing liquid fuel direct injection timing increased thermal efficiency and NOx emission while UHC and CO emission decreased due to stratification of premixed fuel and increasing temperature and in-cylinder pressure rise rate. Using biodiesel with low lower heating value indirect injection of liquid fuel reduced the maximum pressure rise rate resulting in reduction of NOx emission while increasing UHC and CO. Besides, increasing premixed ratio decreased thermal efficiency but increased UHC emission due to over premixed rich charge.

2D CFD Simulation of Water Injection Strategies in a Large Marine Engine

A two-dimensional computational fluid dynamics (2D CFD) simulation of a low-speed two-stroke marine engine simulation was performed in order to investigate the performance of 2D meshes that allow the use of more complex chemical schemes and pollutant formation analysis. Various mesh density simulations were compared with a 3D mesh simulation and with the experimentally obtained cylinder pressure. A heavy fuel model and a soot model were implemented in the software. Finally, the influences of three water injection strategies were simulated and evaluated in order to investigate the capability of the model and the influence of water injection on NOx formation, soot formation, and engine performance. We conclude that the direct water injection strategy reduces NOx emissions without adversely affecting the engine performance or soot emissions. The other two strategies—Intake air humidification and direct injection of fuel–water emulsion—reduced NOx emissions but at the cost of higher soot emissions or reduced engine performance.

Impact of fuel and engine operating conditions on efficiency of a heavy duty truck engine running compression ignition mode using energy and exergy analysis

Gasoline compression ignition using a single gasoline-type fuel for direct/port injection has been shown as a method to achieve low temperature combustion with low engine-out NOx and soot emissions and high indicated thermal efficiency. However, key technical barriers to achieving low temperature combustion on multi-cylinder engines include the air handling system (limited amount of exhaust gas recirculation) as well as mechanical engine limitations (e.g. peak pressure rise rate). In light of these limitations, high temperature combustion with reduced amounts of exhaust gas recirculation appears more practical. Previous studies by the authors demonstrated that utilizing port and direct injection of E85 gasoline simultaneously resulted in the best performance and the highest brake thermal efficiency of 47.1%, which was 1.2% higher compared to diesel baseline. For further efficiency improvement, a better understanding of energy and exergy loss mechanisms is required. In this work, first and second law thermodynamics analysis were applied to experiments with gasoline compression ignition at an engine speed of 1038 rpm and brake mean effective pressure of 1.4 MPa on a 12.4 L multi-cylinder heavy-duty diesel engine. The impact on the efficiency, losses, and irreversibility with respect to various parameters such as fuel, injection strategy, intake condition, and port injected water mass was quantified. The peak efficiency of ideal cycles and the combined efficiency with a waste heat recovery system were also estimated in this study to assess opportunities for further efficiency gains. It was found that the combustion irreversibility was dominated by the combustion temperature rather than the fuel structure. Despite its highest brake thermal efficiency, E85 gasoline generated the highest exergy destruction due to its lowest combustion temperature. For the same reason, retarding the combustion phasing or adopting a port and direct injection strategy increased the exergy destruction. The combustion duration loss was more notable than the phasing loss and was affected by both the combustion duration and shape of heat release profile. Water port injection increased the exhaust energy, but the available energy dropped significantly attributed to the decrease in the exhaust temperature, rendering waste heat recovery ineffective. The second law analysis serves as a helpful tool in conjunction with the first law analysis to explore pathways to maximize engine efficiency.

Performance improvement of self-humidifying PEM fuel cells using water injection at various start-up conditions

A critical issue in self-humidifying proton electrolyte membrane (PEM) fuel cells is to achieve stable performance during start-up. In this study, the start-up characteristics of self-humidifying PEM fuel cells are investigated at various temperatures and voltages. Aquivion and Nafion are used as electrolytes for the performance comparison. Moreover, to overcome start-up failure, the direct water injection strategy is proposed and tested in the self-humidifying PEM fuel cell according to the injection side and amount of injected water. Generally, Aquivion membranes exhibit better start-up performance than Nafion membranes in the self-humidifying PEM fuel cell owing to its higher water absorption capability. The water injection into the anode side is more effective than that into the cathode side in achieving high stability and steady-state current density in the self-humidifying PEM fuel cells. With the water injection during start-up, the steady-state current density of the self-humidifying PEM fuel cell with Aquivion is 32% on average higher than that with Nafion. In addition, the optimal amount of water injection is dependent on the water absorption capability of the membrane at the start-up conditions.

Ignition control in a gasoline compression ignition engine with ozone addition combined with a two-stage direct-injection strategy

To control the ignition timing in a gasoline compression ignition (GCI) engine, ozone (O3) was introduced into the intake air. The O-radicals are decomposed from the O3 above 550 K during the compression stroke, and combine into oxygen (O2) in a very short time. The authors adopted two-stage direct injection to mix the fuel injected into the cylinder at very early timings with the O-radicals, before a reduction of the O-radicals would take place. The ignition timing of the second fuel injection for the main combustion is controlled by the heat release from the first fuel injection. In this paper, engine experiments were performed to examine the feasibility of the ignition control with a primary reference fuel, octane number 90 (PRF90). The O3 concentration, the quantity, and the timing of the first injection were changed as experimental parameters. The results showed that a very small quantity of O3, tens of ppm, is sufficient to promote the heat release of the first injected fuel. The heat release increases with the O3 concentration and the quantity of fuel in the first injection. The addition of O3 has no other impact on the ignition when the first injection timing is retarded to around −40°CA ATDC. In this manner, it is possible to control the ignition delays and to alter the combustion state from typical diesel combustion to premixed compression ignition combustion.