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In port fuel injection (PFI) gasoline engines, combustion fluctuations are caused by the interaction of various factors during ignition. Variations in the fuel deposition on the intake port walls cause fluctuations in the fuel supply to the combustion chamber and in the fuel concentration distribution, which causes knocking. In addition, when a large amount of fuel deposition occurs, it flows into the cylinder in liquid form without vaporizing, generating unburned hydrocarbons. In the previous report, we confirmed that the fuel adhesion amount on the port wall can be reduced by increasing the fuel injection pressure. In this paper, we investigated fuel atomization under even higher injection pressure conditions than the injection pressure range commonly used in intake port injection, with the aim of further reducing the amount of adhesion. In this paper, shadowgraph photography and Super High Spatial Resolution Photography were used to visualize and measure the free-spray jet morphology and atomization characteristics. The effect of high injection pressure to like direct injection, which on the Jet configuration and atomization characteristics of the spray. The results showed that the droplet diameter changed significantly from 1 to 3 MPa (Wavy region) to 4 MPa (Spray region), but no significant change was observed after 8 MPa (Spray region, Spray region with secondary breakup), and that the droplet diameter did not decrease after 8 MPa. [ABSTRACT FROM AUTHOR]

There are a large number of applications in which hydrogen internal combustion engines represent a sensible alternative to battery electric propulsion systems and to fuel cell electric propulsion systems. The main advantages of combustion engines are their high degree of robustness and low manufacturing costs. No critical raw materials are required for production and there are highly developed production plants worldwide. A CO 2 -free operation is possible when using hydrogen as a fuel. The formation of nitrogen oxides during hydrogen combustion in the engine can be effectively mitigated by a lean-burn combustion process. However, achieving low NO x raw emissions conflicts with achieving high power yields. In this work, a series industrial diesel engine was converted for hydrogen operation and comprehensive engine tests were carried out. Various measures to improve the trade-off between NO x emissions and performance were investigated and evaluated. The rated power output and the maximum torque of the series diesel engine could be exceeded while maintaining an indicated specific NO x emission of 1 g/kWh along the entire full load curve. In the low-end-torque range, however, the gap to the full load curve of the series diesel engine could not be fully closed with the hardware used. • Converted hydrogen engine exceeds the rated power output and the maximum torque of the series diesel engine. • Indicated specific NO x raw emissions at full load in the entire speed range are less than 1 g/kWh. • Indicated thermal efficiency map is similar to that of the series diesel engine. • Minimum modifications to the series diesel engine hardware. [ABSTRACT FROM AUTHOR]

With the continuous development of hydrogen energy technology, mixing hydrogen has become a potential method to enhance the performance of natural gas engines and reduce emissions. Aiming to offer guidance for optimizing strategies for mixing hydrogen from the perspectives of knock control and thermal efficiency enhancement, a three-dimensional model of a commercial heavy-duty natural gas engine is constructed based on the actual boundary conditions from a high load bench test. In this study, simulations were conducted under conditions where the hydrogen volume fraction ranged from 0% to 40%. The study explored the effects of two injection strategies, port fuel injection of hydrogen-enriched natural gas (PFI) and port fuel injection of natural gas combined with direct injection of hydrogen into the cylinder (PFI + DI), on engine knocking, performance, and emissions. Results indicate that for various injection strategies, there is an increasing trend in knock intensity (KI) with the higher hydrogen mixing ratio. When the hydrogen volume fraction exceeds 20%, the timing of direct hydrogen injection significantly affects KI. This effect is mainly caused by the distribution of unburned hydrogen at the knock onset crank angle (KOCA). Compared to other injection strategies, the PFI + DI strategy when the direct hydrogen injection time at 120°CA BTDC results in a high concentration of hydrogen near the spark plug at the ignition moment, combined with good mixture uniformity in the cylinder. This leads to the shortest CA0-10 and CA10-90, and achieves a maximum indicated thermal efficiency (ITE) of 44.68% under 20% hydrogen volume fraction. Compared to the original natural gas engine, the ITE increased by 2.9% and the NO x emissions increased by 166%, while the HC and CO emissions decreased by 88% and 53%. • Effects of different hydrogen mixing strategies on a natural gas engine are studied. • Knock intensity correlates with unburned hydrogen distribution at knock onset crank angle. • Hydrogen mixing methods affect mixture uniformity and TKE in cylinder. • At 20% hydrogen volume fraction, direct hydrogen injection timing of 120°CA BTDC maximizes ITE. [ABSTRACT FROM AUTHOR]

In order to avoid the food vs. fuel debate, other than food-based products, agricultural products are effective sources for fuel development. Various parts of plants and trees are used to produce sustainable, low-viscous biofuels, which are gaining much attraction due to their superior burning abilities. The turpentine biofuel produced from pine tree oil has been used for gasoline engines because of its better calorific value and other notable benefits. An attempt has been made to investigate the suitability of turpentine biofuel as a 50% replacement for gasoline in automotive applications to identify the optimum blend ratio. In this study, the experiments are conducted in the port-fuel-injected gasoline engine at different loading conditions of 0 kg to 15 kg at 1800 rpm. Using turpentine blends in a port-fuel-injected SI engine, performance characteristics have been observed with up to a 3–5% improvement in brake thermal efficiency and fuel economy for all concentrations of turpentine biofuel due to their higher calorific value. However, the implementation of turpentine biofuel has shown remarkable reductions in unburnt hydrocarbons by 50% and carbon monoxide emissions by 90% due to its superior burning ability. However, this reduction is not witnessed in oxides of nitrogen and carbon dioxide emissions due to the lower octane number and higher viscosity, which result in a 30% and 5% increase, respectively. Interestingly, the combustion characteristics are observed to be better at part load operations for lower concentrations (30%) of turpentine biofuel in the blends, and this trend has not been noticed at higher concentrations of turpentine biofuel. Finally, it has been concluded that turpentine biofuel would be a better option for the partial replacement of gasoline by up to 30%. However, for further investigation, the anti-knocking characteristics of the turpentine biofuel need to be improved, especially in 40% and 50% turpentine biofuel blends using suitable anti-knocking agents. [ABSTRACT FROM AUTHOR]

Port Fuel Injection (PFI) system in hybrid gasoline engines is frequently in cold condition due to use for electricity generation. Under cold condition, the fuel film forms on the intake port wall does not evaporate completely during the cycle, and the injected fuel spray impinges on it in the next cycle. In this paper, the process of fuel film formation under multi-cycle fuel injection condition is analysed by applying the Total Internal Reflection Laser Induced Fluorescence method. In addition, the particle size distribution of spray droplets was measured in quiescent conditions with Super High Spatial Resolution Photography method, which allows for whole spray imaging while maintaining the spatial resolution of small droplets. As a result, the fuel adhesion mass per injection increases as the critical Weber number increases with repeated fuel injections under quiescent conditions. Under cross flow conditions, fuel mass impinging on the wall is much smaller than under quiescent conditions. Accordingly, the fuel adhesion mass per injection is almost constant with repeated fuel injections because of the small increase in the critical Weber number. [ABSTRACT FROM AUTHOR]

In this study, the effects of varying excess air ratios on a 2.0 L naturally aspirated (NA) hydrogen-fueled spark ignition (SI) engine were evaluated under low-load conditions by using port fuel injection (PFI) and direct injection (DI) systems. The engine speeds chosen were 1,200 rpm and 2,000 rpm. The excess air ratio was varied between 1.0 and 2.7 by controlling the throttle and hydrogen fuel rate under a brake mean effective pressure of 0.4 MPa. The combustion mechanism, net indicated thermal efficiency (ITE), brake thermal efficiency (BTE), gas exchange efficiency, mechanical efficiency, and engine-out nitrogen oxide (NOx) emissions were mainly discussed. The results indicated that the main combustion duration of PFI was shorter than that of DI due to its homogeneity, and the ITE values of PFI were similar or slightly lower than those of DI. However, as the mechanical efficiency of DI was higher than that of PFI, the BTE values of DI were always higher than those of PFI (the maximum BTE was 39.7 %). The NOx reduction potential of DI was superior to that of PFI due to stratified combustion, and its lowest value was 0.03 g/kWh. In addition, as the CO2 concentration in the exhaust gas increased, the brake-specific CO2 reduced (< 5.71 g/kWh). [ABSTRACT FROM AUTHOR]

Modern gasoline engines have to meet increased stringent emission requirements along with the demand of a better fuel economy. This has led to a transition from carburetor to port fuel injection (PFI) mode in developing world for engines comprising mostly of two- and three-wheeler segments and small-scale power generation sets. Therefore, a thorough understanding on mixture formation and combustion phenomenon is needed to further enhance PFI engines. Planar laser-induced fluorescence (PLIF) has proved to be a successful optical diagnostic technique that can provide very high spatial resolution images of fuel distribution in the region of interest. This has led to a direct visualization of fuel distribution with evaluation of both spatial and temporal variations. It has furthered understanding of various engines parameters that affect mixture formation process. Various exciting concepts about fuel stratification have been proposed over the years for enhanced engine operations at lean equivalence ratios. These have been verified and optimized by information gathered from PLIF. In this review article, the authors explain mixture formation process right from the point of fuel injection in intake manifold, the subsequent formation of fuel films and its impact on engine operation. Several PLIF studies on fuel distribution, its spatial and cycle-to-cycle inhomogeneities, effects of injection timing, flow field, equivalence ratio and engine speed on mixture formation have been discussed in separate subsections. Furthermore, studies involving concepts of fuel stratification have also been briefly discussed. [ABSTRACT FROM AUTHOR]

Rising engine efficiency, increasingly stringent exhaust limits, and the use of synthetic and renewable fuels are all factors that demand a deeper knowledge of the combustion process. State-of-the-art investigations employ optical and laser-optical measurement techniques that rely on having optical access to the engine. In this paper, a new endoscopic system that provides full optical access to a high-speed large-bore engine is compared by thermodynamic experimentation to the equivalent all-metal engine. This comparison provides an insight into the altered combustion behavior resulting from modifying the engine to accommodate the optical elements. The successfully realized concept consists of two individually usable access points integrated in an engine with a bore of 170 mm and a stroke of 210 mm. The lateral endoscopic access is designed for full-load operating conditions and provides the best comparability to an all-metal engine. It is compared directly to the all-metal engine in the present investigations. Despite the changes in engine-out emissions from the optical engine, the experimental results display relatively equal combustion behavior in both setups. The lateral endoscopic access is then extended by adding a fisheye endoscope in place of one exhaust valve. This setup is compared to findings obtained with the endoscopic lateral access. The investigations reveal further deviations of the combustion process due to the more extensive modifications needed to fit the fisheye endoscope to the cylinder head. Nevertheless, the results display an overall good level of comparability of the combustion behaviors in these setups and, in turn, of the validity of further fundamental experiments based on the optical engine. [ABSTRACT FROM AUTHOR]

The following paper presents thermodynamic and optical investigations of hydrogen-enriched methane combustion, showing the potential of a hydrogen admixture as a means to decarbonize stationary power generation. The optical investigations are carried out through a fisheye optical system directly mounted into the combustion chamber, replacing one exhaust valve. All of the tests were carried out with constant fuel energy producing 16 bar indicated mean effective pressure. The engine under investigation is a port-fueled 4.8 L single-cylinder large-bore research engine. The test series compared the differences between a conventional spark plug and an unscavenged pre-chamber spark plug as an ignition system. The fuel blends under investigation are 5 and 10%V hydrogen mixed with methane and pure natural gas acting as a reference fuel. The thermodynamic results show a beneficial influence of the hydrogen admixture on both ignition systems and for all variations concerning the lean running limit, combustion stability and indicated efficiency, with the most significant influence being visible for the tests using conventional spark plugs. With the unscavenged pre-chamber spark plug and the combustion of the 10%V hydrogen admixture, an increase in the indicated efficiency of 0.8% compared to NG is achievable. The natural chemiluminescence intensity traces were observed to be predominantly influenced by the air–fuel equivalence ratio. This results in a 20% higher intensity for the unscavenged pre-chamber spark plug for the combustion of 10%V hydrogen compared to the conventional spark plug. This is also visible in the evaluations of the flame color derived from the dewarped combustion image series. The investigation of the torch flames also shows a difference in the air–fuel equivalence ratio but not between the different fuels. The results encourage the development of hydrogen-based fuels and the potential to store surplus sustainable energy in the form of hydrogen in existing gas grids. [ABSTRACT FROM AUTHOR]

In a spark-ignition engine with intake port fuel injection, fuel is sprayed into the intake port under flow conditions and atomized droplets flow into the cylinder, some of which adhere to the intake port wall and form a liquid film. The liquid film adhered to the intake port is a factor in combustion fluctuations due to cycle-to-cycle variations of the air-fuel mixture in the cylinder, as well as unburned hydrocarbons and soot emissions. In this study, a wind tunnel experimental apparatus simulated an intake port was constructed to understand the wall adhesion characteristics of fuel spray in the intake port during engine startup and cold startup conditions. Scattered light photography was used to observe fuel spray characteristics in static and flow conditions, and total internal reflection laser-induced fluorescence (TIR-LIF) was applied to analyze the wall adhesion characteristics of fuel sprays. As a result, in the static field, the spray interaction increased with increasing injection pressure, and the amount of wall adhesion increased. However, in a flow field, the spray follows the flow as the injection pressure increases, and the amount of adhesion decreases. [ABSTRACT FROM AUTHOR]

Port fuel injection is an important technical route in methanol engines. To obtain a theoretical basis for injector arrangement and injection strategy development in methanol engines, an optimal experimental platform based on diffuse back-illumination and the refractive index matching method (RIM) was designed and built in this study. The experiments on the behavior of low-pressure methanol spray-wall impingement and wall film were carried out and the influence of the three boundary conditions of spray distance (Dimp), wall temperature (Twall), and injection pressure (Pinj) were analyzed comprehensively. Results showed that with the increase of Dimp, the overall shape of spray before impinging the wall changed from conical to cylindrical. The impinging spray height Hi and impinging spray width Wi increased with the decrease of Dimp and the increase of Pinj. Adhesive fuel film mass Mf increased with the increase of Dimp due to the decrease of kinetic energy during wall impact. In addition, the increase of the wall temperature Twall reduced Mf due to evaporation, but when Twall reached 423 K, Mf rebounded due to the Leidenfrost effect. The results of this study are helpful to improve the accuracy of the numerical methanol engine model. [ABSTRACT FROM AUTHOR]

• A fast-running model that quantifies the methanol evaporative cooling is proposed. • The model shows excellent predictability. • Methanol evaporates mostly as a liquid film in the intake of ICE. • Surface temperature of the methanol liquid film is critical for its evaporation rate. Renewable methanol is one of the most promising alternative fuels for internal combustion engines. However, its much higher latent heat of vaporization compared to traditional fossil-based hydrocarbon fuels poses new challenges. On both spark-ignition (SI) engines and dual-fuel (DF) engines, methanol can be introduced through injectors installed in the intake path, with its evaporation then causing a cooling effect to the intake air flow. While this is beneficial in mitigating knock with both SI and DF operations, it could potentially lead to cold-starting issues in SI engines and incomplete combustion in DF engines. To properly model the in-cylinder behaviour, the mixture temperature after methanol injection needs to be accurately predicted. A simple yet effective methanol evaporation model based on the liquid droplet and film evaporation mechanisms is thus proposed here to quantify the evaporative cooling effect from methanol injection. The model first treats the methanol spray as a group of droplets with identical size, and after reaching the wall the model assumes that the remaining methanol forms a thin liquid film. The evaporation rates and the consequent temperature drops of these two modes are calculated separately. The calculation results indicate that only a negligible amount of methanol evaporates as droplets, with the predicted temperature drops agreeing well with the validation datasets when taking only the film evaporation into account. The key factor for this good agreement is that the balance between the heat and mass transfer needs to considered when evaluating the surface temperature of a liquid methanol film. The proposed model also suggests that the droplet evaporation can be greatly improved with an injection angle nearly parallel to the air flow, or a finer initial droplet size. Both measures are more effective than increasing the air temperature before injection. [ABSTRACT FROM AUTHOR]

In recent decades, research on alternative fuel engines is becoming more and more popular. Compressed natural gas (CNG) has the advantages of abundant reserves and a lower cost. It can reduce vehicle emissions relatively quickly and has little impact on the entire transportation infrastructure. As the fourth generation of a gas fuel supply method, gas fuel direct injection (DI) technology can effectively avoid volumetric efficiency reduction and power reduction problems of the port fuel injection (PFI) method. However, the former's mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. In order to improve the in-cylinder mixing uniformity, the in-cylinder mixing process of the CNG-fueled engine is taken as the research object in this study. The computational fluid dynamics (CFDs) models of the mixing process for the PFI and DI modes are established, and their mixing uniformities are compared. Besides, based on the authors' previous research, the influence mechanism of the piston crown shape and fuel injection angle on the mixing process of the CNG DI engine is explored. The results show that the probability distribution frequency (PDF) of the best mixture concentration region (BMCR) is as high as 72% for the PFI mode, which is much higher than for the DI mode. The shorter jet impingement distance of the flat top piston leads to higher turbulent kinetic energy (TKE) intensity, and the in-cylinder mixing uniformity will be improved. When gas fuel is injected into an area with a higher in-cylinder TKE, the average in-cylinder TKE will be higher, and the in-cylinder mixture will be more homogeneous. [ABSTRACT FROM AUTHOR]

Hydrogen internal combustion engine (H 2 ICE), heralded as the most promising application of hydrogen energy, represents an excellent pathway for achieving energy transformation and carbon neutrality objectives. However, constrained by the primary obstacles of H 2 ICE, including abnormal combustions and NO X emissions, the port fuel injection hydrogen internal combustion engine (PFI- H 2 ICE) exhibits some shortcomings in power output despite its relatively lower cost. In comparison, the direct injection strategy is unaffected by air displacement and can achieve stratified combustion by delaying the injection timing to organize the in-cylinder mixture, known as the Late Direct Injection (LDI), which further enhances power and economy. However, due to the stratified combustion, the NO X emissions of LDI increase significantly compared to the PFI. On the other hand, Exhaust Gas Recirculation (EGR), as the simplest strategy to implement, demonstrates robust effectiveness in balancing power and emissions, and reducing the risk of abnormal combustions. To alleviate concerns about emissions, the integration of EGR is one of the most promising directions for H 2 ICE. Therefore, this study compares and analyzes the effects and differences of PFI and LDI combined with EGR on combustion and emissions characteristics. The experimental results indicate that the PFI strategy characterized by a homogeneously mixed air–fuel mixture exhibits advantages in maintaining relatively high brake thermal efficiency (BTE) and reducing NO X emissions under low loads due to the implementation of lean burn. The addition of EGR slows down the flame speed and reduces the in-cylinder temperature, leading to a significant reduction in NO X emissions as the EGR rate increases, especially under high loads. On the other hand, due to the air displacement effect, the PFI strategy consumes part of the air entering the cylinder, resulting in a comprehensively lower cylinder pressure and heat release rate (HRR) than LDI, along with equally diminished overall levels in break mean effective pressure (BMEP) and NO X emissions. Nonetheless, when combining EGR and LDI's stratified combustion under high loads, not only an 84.4% reduction in NO X emissions is achieved, but also a comparable or even lower NO X emission level is reached compared to PFI under the same λ conditions, while maintaining relatively high BTE and BMEP. Therefore, the combination of EGR and LDI is more promising in balancing the power performance and NO X emissions of H 2 ICE. Moreover, Coefficient of Variation in Indicated Mean Effective Pressure (COV IMEP) are more significantly influenced by spark timing, with relatively minor effects attributed to EGR rates. Given the adoption of Minimum Spark Advance for Best Torque (MBT) and near-MBT in spark timing, the COV IMEP remains below 1.3% across most operational conditions. For H 2 emissions, generally increase with the rise in EGR rate and λ due to the decrease in flame speed and temperature. • EGR is one of the most effective strategies for balancing power output and NO X emissions in H 2 ICE. • The addition of EGR increases H 2 emission in most operating conditions. • Late direct injection has higher power, economy and emissions than port fuel injection due to stratified combustion. • Late direct injection combined with EGR can reduce NO X emissions at higher loads. [ABSTRACT FROM AUTHOR]

Hydrogen energy is one of the most promising sources of carbon neutrality from well to wheel. Among various applications of hydrogen energy, hydrogen internal combustion engines serve as the critical technical pathway. Nevertheless, several challenges persist, primarily related to abnormal combustion resulting from excessive flame propagation velocity. Of these challenges, backfire emerges as the most recurrent and pressing issue to be resolved in the port fuel-injected hydrogen internal combustion engine (PFI-H 2 ICE). In order to delve into the characteristics and mechanisms of backfire, this study concentrates on a critical internal parameter, namely the start of injection (SOI), and comprehensively assesses the backfire occurrences under varying lambda and engine speed conditions. Experimental findings reveal that SOI encompasses one of the pivotal factors influencing backfire. Backfire predominantly arises within two ranges of SOI conditions: the region before −430 degCA ATDC (Zone I) and the stretch between −360 degCA ATDC and − 280 degCA ATDC (Zone II). In the process of employing EGR to depress the effects of backfire on subsequent tests, it was incidentally found that the Universal Exhaust Gas Oxygen Sensor (UEGO) installed on the intake manifold for executing EGR rate calculations acted as a hotspot (with temperatures exceeding 100 °C). This not only intensified the backfire strength and the scope in Zone I but also caused the most severe backfire events to occur after −270 degCA ATDC (in Zone III). Despite this, the EGR strategy still demonstrated a significant backfire suppression effect, only exhibiting almost no influence on backfire caused by hotspots within the intake manifold. With an escalation in engine speed, the intensity of backfire diminishes, and the range of backfire occurrence decreases accordingly. By exercising control over SOI within the operating range from -430degCA to -360degCA ATDC (Zone A), the risk of backfire can be dramatically reduced, thereby achieving nearly backfire-free operation. Detailed analysis of cylinder pressure indicates that backfire may also give rise to other abnormal combustions, such as misfire, pre-ignition, and knock, in subsequent cycles. Moreover, this effect amplifies in tandem with an increase in mixture concentration. A certain degree of mutual promotion among diverse abnormal combustions is also observed. This study furnishes the most direct and practical foundation for internal and external strategies in the realm of backfire control. • The backfires are concentrated within two specific SOI operating conditions ranges. • SOI scheduling is critical in backfire control, with the safest position being in a specific range before IVO. • The hotspot within the intake manifold increases the backfire strength and leads to the strongest backfire. • A 12% EGR can reduce half of the backfire operating regions and decrease backfire strength. • Backfire may trigger other abnormal combustions, especially in relatively rich-burn conditions. [ABSTRACT FROM AUTHOR]

The following paper presents thermodynamic and optical investigations of the natural flame and OH radical chemiluminescence of a hydrogen enriched methane combustion compared to natural gas combustion. The engine under investigation is a port-fueled unscavenged prechamber 4.8 L single cylinder large bore engine. The blends under consideration are 2%V, 5%V,10%V, and 40%V of hydrogen expected to be blended within existing natural gas grids in a short and mid-term timeline in order to store green energy from solar and wind. These fuel blends could be used for stabilization of the energy supply by reconverting the renewable fuel CH4/H2 in combined heat and power plants. As expected, admixture of hydrogen extends the ignition limits of the fuel mixture toward lean ranges up to an air-fuel equivalence ratio of almost 2. No negative effect on combustion is observed up to an admixture of 40%V hydrogen. At 40%V hydrogen, abnormal combustion like backfire occurs at an air-fuel equivalence ratio of 1.5. The higher mixtures exhibit increased nitrogen oxide emissions due to higher combustion chamber temperatures, while methane slip and CO emissions are reduced due to more complete combustion. The optical investigation of the natural flame and OH radical chemiluminescence are in good agreement with the thermodynamic results verifying the more intense combustion of the fuel blends by means of the chemiluminescence intensity. Further, lube oil combustion and a continuing luminescence after the thermodynamic end of combustion are observed. [ABSTRACT FROM AUTHOR]

The application of hydrogen in internal combustion engines (ICE) has attracted widespread attention. However, due to the low ignition energy, high flame propagation speed, and wide combustible range of hydrogen, it is easy to cause abnormal combustion phenomena such as backfire in the port fuel injected (PFI) hydrogen-fueled engine. When a backfire occurs, the combustible mixture burns in the intake, resulting in a decrease in the volumetric efficiency of the engine, which may cause it to misfire or shut down in severe cases. Fast and accurate detection of backfire events is essential to take targeted control measures. In this research, a backfire detection system based on dual intake manifold absolute pressure (MAP) sensors were designed, with two MAP sensors installed on the intake manifolds of the first and fourth cylinders, and four gas injectors were installed on the intake manifold to convert the gasoline ICE into a hydrogen-fueled ICE. During the experiment, the engine speed was stabilized at 1000 rpm, the throttle valve was fully opened, and the intake pressure was maintained at 100 kPa.The test results show that the system can accurately determine the location and intensity of backfire occurrence. This method provides a basis for precise control of backfiring. • Set up two MAP sensors to monitor the backfiring of the hydrogen ICE. • MAP sensors allow accurate monitoring of backfiring. • Need to optimize valve strategy and injection strategy for hydrogen ICE. [ABSTRACT FROM AUTHOR]

Ethanol, produced from biomass, is a renewable fuel that can be an attractive alternative fuel to gasoline for the increasing concerns of energy security and the environment. In the present work, combustion characteristic of ethanol (E100) fueled spark-ignition engine is compared with base gasoline fuel, and consecutively evaluated the cycle-to-cycle variations (CCV) of the engine parameters. These investigations were performed on a 250cc air-cooled four-stroke single-cylinder port-fuel injection spark-ignition engine. The engine was operated at 3500 rpm and 4000 rpm of engine speed while maintaining the same loads for ethanol and gasoline. It was found from the results that the peak in-cylinder pressure (Ppeak) is lower with ethanol than gasoline at a given load. The Ppeak decreased from 27.5 to 25.5 bar when ethanol was used in the engine at 3500 rpm and 5 Nm load instead of gasoline. Moreover, the mass fraction burned of the air-fuel mixture was faster for ethanol as compared to gasoline. The CCV analysis showed that CCV of Ppeak and location of Ppeak (IMEP) were lowered for ethanol compared to gasoline. A decrement in the coefficient of variation (COV) of Ppeak and IMEP from 11.6% to 8.3% and 12.6% to 11.7%, respectively, were observed when ethanol was utilized in the engine instead of gasoline at 3500 rpm and 5 Nm load. This resulted in a decrease in the COV of IMEP and engine speed by 2.8% and 0.25%, respectively, for ethanol as compared to gasoline. This study indicates that the combustion stability is better for ethanol-fueled spark ignition engine as compared with gasoline fuel. [ABSTRACT FROM AUTHOR]

Analysis of plastic oil obtained from waste plastic through pyrolysis process, as an alternative to biodiesel is presented in this paper. The HCCI engine is considered for experimental validation of combustion performance and emission characteristics. To accumulate pyrolysis oil as fuel, the design modifications were made in external mixture formation on the existing computerised 4-stroke, single cylinder, water cooled, direct injection kirloskar diesel engine connected with eddy current dynamometer to satisfy HCCI conditions. HCCI engine can be worked on wide assortment of fuels beginning from diesel to different blends (WPPO 5%,10%,15% and 20% by volume) of biodiesel .The designed additional device connected to the engine is utilised for fuel vaporisation and mixture arrangement. In the experimental study, the combustion results were initiate to be of 39.69 % higher Rate of Heat Release (RoHR) for biodiesel HCCI as compared with diesel HCCI. Higher brake thermal efficiency (BTE) was found 37 % without exhaust gas recirculation (EGR) at WPPO 20 % biodiesel blend. And also found 50 % and 65 % reduction in NOx emission and 18 % and 28 % reduction in smoke opacity are obtained for biodiesel vapour induction without EGR and biodiesel vapour induction with 15 % EGR as compared with diesel fuel. The CO (0.34 %), and UHC (2.15 %) emissions are increases with 15 % EGR, but the emissions are within the standard limits specified by the emissions standards.

The following paper presents thermodynamic and optical investigations of hydrogen-enriched methane combustion, showing the potential of a hydrogen admixture as a means to decarbonize stationary power generation. The optical investigations are carried out through a fisheye optical system directly mounted into the combustion chamber, replacing one exhaust valve. All of the tests were carried out with constant fuel energy producing 16 bar indicated mean effective pressure. The engine under investigation is a port-fueled 4.8 L single-cylinder large-bore research engine. The test series compared the differences between a conventional spark plug and an unscavenged pre-chamber spark plug as an ignition system. The fuel blends under investigation are 5 and 10%V hydrogen mixed with methane and pure natural gas acting as a reference fuel. The thermodynamic results show a beneficial influence of the hydrogen admixture on both ignition systems and for all variations concerning the lean running limit, combustion stability and indicated efficiency, with the most significant influence being visible for the tests using conventional spark plugs. With the unscavenged pre-chamber spark plug and the combustion of the 10%V hydrogen admixture, an increase in the indicated efficiency of 0.8% compared to NG is achievable. The natural chemiluminescence intensity traces were observed to be predominantly influenced by the air–fuel equivalence ratio. This results in a 20% higher intensity for the unscavenged pre-chamber spark plug for the combustion of 10%V hydrogen compared to the conventional spark plug. This is also visible in the evaluations of the flame color derived from the dewarped combustion image series. The investigation of the torch flames also shows a difference in the air–fuel equivalence ratio but not between the different fuels. The results encourage the development of hydrogen-based fuels and the potential to store surplus sustainable energy in the form of hydrogen in existing gas grids.

A port injection engine that supplies hydrogen to the intake manifold or port exhibits a low intake air amount and torque output. The torque output is limited by backfire. In the present study, the performance and efficiency of a port injection-type hydrogen engine using the fuel injector of a natural gas engine is investigated at various engines speeds under wide open throttle conditions and two operation strategies, i.e., limiting nitrogen oxide emission and maximizing the torque. The increase in electrode temperature is reduced by increasing the heat rating number of the spark plug or reducing the ignition energy applied to the spark plug. Even when the ignition energy is reduced, as the minimum ignition energy of hydrogen is very low, it does not eliminate backfire. However, when a cold-type spark plug is used, backfire is effectively suppressed, resulting in an increase in the maximum torque and a decrease in efficiency. • The excess air ratio must be at least 2.25 to meet the NO x level of 15 ppm. • The excess air ratio and tendency of backfire to occur increase with an increase in engine speed. • Reduction of the ignition energy does not eliminate the occurrence of backfire. • Backfire is effectively suppressed using a cold-type spark plug. [ABSTRACT FROM AUTHOR]

Port fuel injection is an important technical route in methanol engines. To obtain a theoretical basis for injector arrangement and injection strategy development in methanol engines, an optimal experimental platform based on diffuse back-illumination and the refractive index matching method (RIM) was designed and built in this study. The experiments on the behavior of low-pressure methanol spray-wall impingement and wall film were carried out and the influence of the three boundary conditions of spray distance (Dimp), wall temperature (Twall), and injection pressure (Pinj) were analyzed comprehensively. Results showed that with the increase of Dimp, the overall shape of spray before impinging the wall changed from conical to cylindrical. The impinging spray height Hi and impinging spray width Wi increased with the decrease of Dimp and the increase of Pinj. Adhesive fuel film mass Mf increased with the increase of Dimp due to the decrease of kinetic energy during wall impact. In addition, the increase of the wall temperature Twall reduced Mf due to evaporation, but when Twall reached 423 K, Mf rebounded due to the Leidenfrost effect. The results of this study are helpful to improve the accuracy of the numerical methanol engine model.

In the automotive sector, hydrogen is being increasingly explored as an alternative fuel to replace conventional carbon-based fuels. Its combustion characteristics make it well-suited for adaptation to internal combustion engines. The wide flammability range of hydrogen allows for higher dilution conditions, resulting in enhanced combustion efficiency. When combined with lean combustion strategies, hydrogen significantly reduces environmental impact, virtually eliminating carbon dioxide and nitrogen oxide emissions while maintaining high thermal efficiency. This paper aims to assess the potential of using an outwardly opening poppet valve hydrogen direct injection (DI) system in a small engine for light-duty applications. To achieve this, a comparison of performance, emission levels, and combustion parameters is conducted on a single-cylinder spark-ignition (SI) research engine fueled by hydrogen, using both port fuel injection (PFI) and this new direct injection system. Two different engine loads are measured at multiple air dilution and injection timing conditions. The results demonstrate notable efficiency improvements, ranging from 0.6% to 1.1% when transitioning from PFI to DI. Accurate control of injection timing is essential for achieving optimal performance and low emissions. Delaying the start of injection results in a 7.6% reduction in compression work at low load and a 3.9% reduction at high load. This results in a 3.1-3.2% improvement in ISFC in both load conditions considered. • A novel hydrogen medium-pressure direct injection system has been evaluated. • Direct injection improves gross indicated efficiency levels between 0.6%–1.1%. • ISFC gains around 3% are achieved with delayed SoI using a direct injection system. • Nitrogen oxide levels are minimized by combining dilution and injection strategies. • Results hint that controlling stratification may enhance efficiency and pollutants. [ABSTRACT FROM AUTHOR]

In recent decades, research on alternative fuel engines is becoming more and more popular. Compressed natural gas (CNG) has the advantages of abundant reserves and a lower cost. It can reduce vehicle emissions relatively quickly and has little impact on the entire transportation infrastructure. As the fourth generation of a gas fuel supply method, gas fuel direct injection (DI) technology can effectively avoid volumetric efficiency reduction and power reduction problems of the port fuel injection (PFI) method. However, the former’s mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. In order to improve the in-cylinder mixing uniformity, the in-cylinder mixing process of the CNG-fueled engine is taken as the research object in this study. The computational fluid dynamics (CFDs) models of the mixing process for the PFI and DI modes are established, and their mixing uniformities are compared. Besides, based on the authors’ previous research, the influence mechanism of the piston crown shape and fuel injection angle on the mixing process of the CNG DI engine is explored. The results show that the probability distribution frequency (PDF) of the best mixture concentration region (BMCR) is as high as 72% for the PFI mode, which is much higher than for the DI mode. The shorter jet impingement distance of the flat top piston leads to higher turbulent kinetic energy (TKE) intensity, and the in-cylinder mixing uniformity will be improved. When gas fuel is injected into an area with a higher in-cylinder TKE, the average in-cylinder TKE will be higher, and the in-cylinder mixture will be more homogeneous.

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. Furthermore, for high-temperature gasoline compression ignition, an effective aftertreatment system allows high thermal efficiency with low tailpipe-out emissions. In this work, experimental testing was conducted on a 12.4 L multi-cylinder heavy-duty diesel engine operating with high-temperature gasoline compression ignition combustion with port and direct injection. Engine testing was conducted at an engine speed of 1038 r/min and brake mean effective pressure of 1.4 MPa for three injection strategies, late pilot injection, early pilot injection, and port/direct fuel injection. The impact on engine performance and emissions with respect to varying the combustion phasing were quantified within this study. At the same combustion phasing, early pilot injection and port/direct fuel injection had an earlier start of combustion and higher maximum pressure rise rates than late pilot injection attributable to more premixed fuel from pilot or port injection; however, brake thermal efficiencies were higher with late pilot injection due to reduced heat transfer. Early pilot injection also exhibited the highest cylinder-to-cylinder variations due to differences in injector behavior as well as the spray/wall interactions affecting mixing and evaporation process. Overall, peak brake thermal efficiency of 46.1% and 46% for late pilot injection and port/direct fuel injection was achieved comparable to diesel baseline (45.9%), while early pilot injection showed the lowest brake thermal efficiency (45.3%). [ABSTRACT FROM AUTHOR]

Analysis of plastic oil obtained from waste plastic through pyrolysis process, as an alternative to biodiesel is presented in this paper. The HCCI engine is considered for experimental validation of combustion performance and emission characteristics. To accumulate pyrolysis oil as fuel, the design modifications were made in external mixture formation on the existing computerised 4-stroke, single cylinder, water cooled, direct injection kirloskar diesel engine connected with eddy current dynamometer to satisfy HCCI conditions. HCCI engine can be worked on wide assortment of fuels beginning from diesel to different blends (WPPO 5%,10%,15% and 20% by volume) of biodiesel.The designed additional device connected to the engine is utilised for fuel vaporisation and mixture arrangement. In the experimental study, the combustion results were initiate to be of 39.69 % higher Rate of Heat Release (RoHR) for biodiesel HCCI as compared with diesel HCCI. Higher brake thermal efficiency (BTE) was found 37 % without exhaust gas recirculation (EGR) at WPPO 20 % biodiesel blend. And also found 50 % and 65 % reduction in NOx emission and 18 % and 28 % reduction in smoke opacity are obtained for biodiesel vapour induction without EGR and biodiesel vapour induction with 15 % EGR as compared with diesel fuel. The CO (0.34 %), and UHC (2.15 %) emissions are increases with 15 % EGR, but the emissions are within the standard limits specified by the emissions standards. [ABSTRACT FROM AUTHOR]

Automobile numbers are increasing day by day that demand more fuel and produce more emission. In addition, petroleum sources are limited in nature and emission norms are tightening day by day. Those scenarios are motivating the researcher to find non-petroleum clean energy source. Gaseous fuel supplementation is helpful in obtaining the above stated objective. In this study, methane gas supplementation has done to diesel engine. The investigation was carried out to analyze the performance and emission of CI engine using 0–75% substitution of diesel indicated power by methane energy in dual fuel mode at varying load (25%, 50% and 75%). The result shows that brake thermal efficiency (BTE) and relative air fuel ratio decreases with methane energy share (MES), while unaccounted heat loss increases. Here, a comparison of NO and NO 2 emissions have been presented to investigate the non-thermal effect of CH 4 on NO x emission. Combined reduction in nitrogen oxide and soot emission makes the outcomes of this study more suitable to implement for achieving the strict emission norms. Hence, CH 4 augmentation is beneficial at mid and higher load conditions with lower emissions and energy consumption. [ABSTRACT FROM AUTHOR]

The port-injection-type hydrogen engine is advantaged in that hydrogen gas is injected into the intake pipe through a low-pressure fuel injector, and the mixing period with air is sufficient to produce uniform mixing, improving the thermal efficiency. A drawback is that the flame backfires in the intake manifold, reducing the engine output because the amount of intake air is reduced, owing to the large volume of hydrogen. Here, the backfire mechanism as a part of the development of full-load output capability is investigated, and a 2.4-liter reciprocating gasoline engine is modified to a hydrogen engine with a hydrogen supply system. To secure the stability and output performance of the hydrogen engine, the excess air ratio was controlled with a universal engine control unit. The torque, excess air ratio, hydrogen fuel, and intake air flow rate changes in time were compared under low- and high-engine speed conditions with a wide-open throttle. The excess air ratio depends on the change in the fuel amount when the throttle is completely opened, and excess air ratio increase leads to fuel/air-mixture dilution by the surplus air in the cylinder. As the engine speed increases, the maximum torque decreases because the excess air ratio continues to increase due to the occurrence of the backfire. The exhaust gas temperature also increases, except at an engine speed of 6000 rpm. Furthermore, the increase in exhaust gas temperature affects the backfire occurrence. At 2000 rpm, under low-speed and wide-open throttle conditions, backfire first occurs in the No. 4 cylinder because the mixture is heated by the relatively high port temperature. In contrast, at 6000 rpm, under high-speed and wide-open throttle conditions, the backfire starts at the No. 2 cylinder first because of a higher exhaust gas temperature, resulting in a lower excess air ratio in cylinders 2 and 3, located at the center of the engine. • The maximum torque decreases due to the backfire as the hydrogen engine speed increases. • The increase in the exhaust gas temperature affects the backfire with the increase in speed. • The backfire occurs in the No. 4 cylinder under low-speed conditions due to a higher port temperature. • The backfire starts in the cylinders located at the center of the engine under high-speed conditions. [ABSTRACT FROM AUTHOR]

Highlights • Methanol addition reduced oxides of nitrogen emission drastically. • Hydrous methanol further reduces oxides of nitrogen and soot simultaneously. • Artificial Neural Network modeling of performance and emission parameters. • Several error matrices used for confirming robustness of the developed model. Abstract The present work explores the potential of an artificial neural network platform to emulate the performance, emissions and stability indices of an existing single cylinder diesel engine operating in dual-fuel mode with methanol port injection under varying fuel injection pressure. This investigation is further augmented by hydrous methanol injection strategies. Brake power, fuel injection pressure, diesel specific fuel consumption, methanol specific fuel consumption, air flow rate, exhaust oxygen and temperature have been chosen as the model inputs while oxides of nitrogen, unburned hydrocarbon, carbon monoxide, carbon dioxide, soot have been chosen as the emission responses to be modelled along with equivalent brake specific fuel consumption as the performance response and coefficient of variance of indicated mean effective pressure as the stability parameter to be estimated. Absolute, relative and percentage-based statistical error metrics have been employed for model evaluation. The developed model shows an excellent agreement with the experimental data as evident from its extremely low normalized mean square error, symmetric mean absolute percentage error, Normalized root mean square error, mean squared relative error footprint coupled with high coefficient of determination which was observed to be within a range of 0.983–0.9999 and a corresponding Nash Sutcliffe coefficient of efficiency of 85%–99.6%. Furthermore, low Theil uncertainty evaluation and Kullback-Leibler Divergence values imparted a commendable credence of robustness to the estimation capability of the developed model. The present study manifests a computationally efficient and reliable virtual sensing platform to simultaneously emulate the emission-performance and stability parameters of a diesel-methanol partially premixed dual fuel operational paradigms in real time engine control strategies. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the real driving particle number (PN) emissions from two China-6 compliant hybrid electrical vehicles (HEVs) were measured using a certification-level portable emission measurement system (PEMS) and strict adherence to the regulatory procedures for real driving emission (RDE) testing. The results show that the trip-averaged PN emission factors for the port fuel injection (PFI) HEV and the gasoline direct injection (GDI) HEV were 1.15E+12 and 1.71E+12#/km respectively, much higher than the engine-only counterparts and failing the existing RDE limits. Enriched air-fuel mixtures and probably lowered catalyst conversion efficiencies as a result of more frequent engine stop-and-goes of the HEVs are found to be the underlying reasons for the extra PN emissions. The test results also suggest the necessity to amend the power management strategy currently widely used in HEVs to deal with the PN issue. Highlights • Real-word PN emissions of two China-6 HEVs were tested following RDE procedures. • The RDE PN for the PFI and GDI-HEVs were 1.15E+12 and 1.71E+12#/km respectively. • Fuel-rich and low TWC efficiency since frequent engine-starts caused HEVs' more PN. • The power management strategy of HEVs may need amending to cope with high PN. [ABSTRACT FROM AUTHOR]

Gasoline vehicle emission is a major source of urban particulate matter (PM), particularly ultra-fine PM (≤100 nm), exerting adverse health effects. While the PM emissions from port fuel injection (PFI) and gasoline direct injection (GDI) vehicles have been well addressed in previous studies, few studies have reported the PM emission from the new mixed injection (MI) vehicles. Here, we employed a chassis dynamometer to investigate particle emissions under the Worldwide Harmonized Light vehicles Test Cycles (WLTC) from vehicles with three different fuel injection technologies. The PM and particle number (PN) emission factors (EFs) for MI vehicles are 129.53 μg/km and 1.0 × 1013 #/km, respectively. A trend of PFI > MI > GDI is observed for both PM and PN EFs for vehicles with same emission standard. Notably, the PM emissions of MI vehicles are greatly affected by both fuel injection methods at low and medium speeds, but are more significantly affected by PFI at high speeds. MI vehicle shows much lower PM and PN emissions than other vehicles at low-, medium-, and high-speed phases, but substantial hiher ultra-fine PM emission at extra-high speed phase. This is because the insufficient air supplied by naturally-aspirated engine of MI vehicles in the high-load region leads to incomplete combustion and generate large formation of ultra-fine particles. Besides, the gasoline particulate filter reduces 94.5% of PM emission but produces abundant nucleation-mode particles during regeneration at the extra-high speed phase for MI vehicles. Our study gives an insight to the state-of-the-art engine technology, i.e., MI vehicles, and reveals that this new technology is a feasible alternative for simultaneously reducing pollutant emissions from gasoline vehicles. • ●PM and PN emissions from MI vehicles are lower than PFI and GDI vehicles. • The proportion of nucleation-mode particles from MI vehicles is the highest. • GPF regeneration leads to substantial nucleation-mode particle. [ABSTRACT FROM AUTHOR]

Compressed natural gas (CNG) has gained widespread acceptance in the automobile industry due to its clean-burning properties, lower emissions, and superior anti-knock properties. Typically, CNG is used in bi-fuel mode, where it partially replaces gasoline in a conventional gasoline engine. However, because of its gaseous nature, CNG displaces intake air, which reduces the engine's overall power output. One possible solution is to directly inject CNG into the cylinder during the late intake stroke or at the beginning of the compression stroke, which increases the engine's volumetric efficiency and power output. In a previous study, we examined the impact of injection timing on the performance of direct injection (DI) CNG engines under various engine load and speed conditions. However, the intrinsic combustion process, such as flame speed and flame front propagation, could not be investigated. In this study, we attempted to understand DI CNG engines' in-cylinder flame speed and propagation behavior. We developed a combustion model for the DI CNG engine using computational fluid dynamics. We used methane as the surrogate fuel and six cylindrical nozzles with inlet velocity boundary conditions for CNG direct injection. We studied the CNG combustion process and flame speed propagation using a validated chemical mechanism and a look-up table. We made comparisons to evaluate the numerical model against experimental reference data. We also conducted a comparative simulation of DI CNG, port fuel injection (PFI) CNG, and gasoline engines to assess combustion behavior. The combustion duration was longer for the PFI CNG engine than the gasoline engine, but it was reduced for the DI CNG engine. This was due to the DI CNG engine's 40% higher turbulent flame speed than the PFI CNG engine. The combustion of the air-fuel charge was completed within 40° CA after spark ignition. As a result, DI CNG requires a retard in ignition timing. The DI CNG engine showed a 7% higher power output with a 10% increase in volumetric efficiency compared to the PFI CNG engine. However, the power output was still lower than that of the PFI gasoline engine. The DI CNG engine emitted lower NOx and CO emissions than the PFI CNG engine. This study demonstrates the higher turbulent flame speed and rapid flame front propagation characteristics of DI CNG engines over PFI CNG engines, increasing engine efficiency. • Computational modelling of DI CNG engine using surrogate fuel mechanism. • Enhancement of flame speed using DI CNG over PFI CNG engine. • Power recovery up to 7% using DI CNG over PFI CNG engine. • Lower CO and NOx emissions using DI CNG engine. [ABSTRACT FROM AUTHOR]

Light-duty gasoline vehicles have drawn public attention in China due to their significant primary emissions of particulate matter and volatile organic compounds (VOCs). However, little information on secondary aerosol formation from exhaust for Chinese vehicles and fuel conditions is available. In this study, chamber experiments were conducted to quantify the potential of secondary aerosol formation from the exhaust of a port fuel injection gasoline engine. The engine and fuel used are common in the Chinese market, and the fuel satisfies the China V gasoline fuel standard. Substantial secondary aerosol formation was observed during a 4–5 hr simulation, which was estimated to represent more than 10 days of equivalent atmospheric photo-oxidation in Beijing. As a consequence, the extreme case secondary organic aerosol (SOA) production was 426 ± 85 mg/kg-fuel, with high levels of precursors and OH exposure. The low hygroscopicity of the aerosols formed inside the chamber suggests that SOA was the dominant chemical composition. Fourteen percent of SOA measured in the chamber experiments could be explained through the oxidation of speciated single-ring aromatics. Unspeciated precursors, such as intermediate-volatility organic compounds and semi-volatile organic compounds, might be significant for SOA formation from gasoline VOCs. We concluded that reductions of emissions of aerosol precursor gases from vehicles are essential to mediate pollution in China. [ABSTRACT FROM AUTHOR]