Port Fuel Injection Research Articles

Experimental study of spatial distribution of knock events in a turbocharged spark-ignition engine

An experimental investigation on the spatial distribution of knock events in a turbocharged spark-ignition engine for hybrid vehicle applications was conducted by using a multichannel fiber optic method. The knock positions were detected under different conditions to investigate the influence of crucial engine design and operating parameters on the knock characteristics including the spatial distribution in the combustion chamber and its relationship to knock intensity. The measured data reveal that the spatial distribution in the engine with a port fuel injection (PFI) system is mainly located on the exhaust side with insignificant influence of engine speed and load, which is attributed to the elevated thermal load around the exhaust valves. However, the knock events under gasoline direct-injection (DI) conditions were found to occur in more scattered locations with more occurring on the engine front-end and rear-end sides. These results indicate that the in-cylinder fuel-air mixing process may have a significant impact on the knock occurrence spots under DI conditions. The knock positions of the engine with different excessive air ratios, injection timings, and intake-valve timings were also detected, indicating that engine operating parameters have complex influences on the knock-region distribution in a DI engine. In addition, experiments were also carried out in two different cylinders to verify the cylinder-to-cylinder variations in knock regions which may be caused by the engine cooling design. Furthermore, no apparent correlations were observed between the knock position and the knock intensity by analysis of the experimental data.

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

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

Effects of a Self-Pressurized Injection Strategy on the Formation of a Stratified Mixture and the Combustion of an Aviation Kerosene Piston Engine

Abstract The aviation kerosene piston engine (AKPE) is the main power system for small- and medium-sized unmanned aerial vehicles (UAVs). Conventional AKPEs use carburetors or port fuel injection (PFI) as fuel supply, resulting in poor cold start performance and difficulty in forming an economically efficient stratified mixture. In addition, two-stroke AKPEs using carburetors or PFI have serious scavenging losses. These reasons lead to the poor economic performance of conventional AKPEs. Direct injection (DI) can be controlled through precise injection timing to form a stratified mixture. The combustion of stratified mixtures in engines can effectively improve the fuel economy and endurance flight time characteristics of UAVs. As a special DI injector, self-pressurized injectors have great potential in the power field of UAVs. To effectively apply self-pressurized injectors on UAV engines and improve the economy, an engine model and a self-pressurized injector spray model are established and verified in this paper. The single injection strategy and segmented injection strategy for forming stratified mixtures are explored, and the combustion performance is studied. The main conclusions are as follows: the optimal installation angle of the injector is 15 deg, which yields excellent results in the formation of the mixture at this angle. When the fuel injection quantity is small, utilizing a single injection strategy combined with delaying the end of the injection phase (EOIP) can form a stratified mixture. Reducing the angle difference between the EOIP and the ignition timing can improve the power and economy. As the fuel injection quantity is large, a stratified mixture can be formed through two-stage injection. When the fuel injection ratio is 4:1, the uniformity of the mixture distribution in the combustion chamber is significantly improved. Adjusting the second EOIP between a 35 deg crank angle (CA) before top dead center (BTDC) and a 30 deg CA BTDC can achieve a stratified mixture with good economy and power performance.

Effects of dual injection strategies on combustion, heat-work conversion process and emissions of a spark ignition engine fuelled with E20 blends

In this paper, the combustion, heat-work conversion process and emission characteristic at high compression ratio for the spark ignition engine fuelled with E20 (20 % ethanol, 80 % gasoline) fuel were investigated under ultra-lean burn conditions. Specifically, the direct injection (DI) mode combined with port fuel injection (PFI) mode strategy was used in the experiments. In addition, the dual injection strategies were comprehensively investigated by using different fuel injection masses and injection timing. The results indicated that using optimal injection timing and reasonable injection masses can improve heat-work conversion efficiency and combustion efficiency, combustion stability in the test engine. Furthermore, under the lean combustion model, using earlier injection timing could not only inhibit the soot production, but also decrease the nitrogen oxides formation. Compared to the equivalence ratio at 0.82 and DI injection timing at 120 °CA bTDC, soot and NOX emissions were respectively reduced by 14.93 %–26.6 % and 39.84 %–73.56 % under the equivalence ratio at 0.685 and DI injection timing at 180 °CA bTDC. This study provides an optimization direction for the application of ethanol-gasoline blends in the internal combustion engine (ICE) engines for high efficiency and clean combustion.

Impact of medium-pressure direct injection in a spark-ignition engine fueled by hydrogen

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.

Performance and emission analysis of ammonia-ethanol and ammonia-methane dual-fuel combustion in a spark-ignition engine: An optical study

In light of the pressing need to address climate change, it is imperative to take immediate action to reduce conventional hydrocarbon fuel demand. In pursuit of achieving decarbonization goals, it has become apparent that modern internal combustion engines need to adopt either carbon–neutral fuels or fuels with lower hydrocarbon content. To this end, there are several options available including alternatives such as ammonia (NH3), hydrogen (H2), methane (CH4), methanol (CH3OH), and ethanol (C2H5OH). These fuels offer the potential to be produced in a manner that is either carbon–neutral (the latter two) or entirely free of carbon emissions (the former two), making them an ideal choice for powering advanced IC engines with minimum climate impact. The use of ammonia as a fuel has the potential to significantly reduce the demand for conventional fuels and decrease the emission of harmful pollutants like CO, CO2, particulates, and unburned hydrocarbons during combustion. However, as a combustion fuel, it poses several challenges, including a low burning velocity, narrow flammability range, and instabilities arising during the combustion process. This study compared the two different dual fuel approaches, mixing ammonia-ethanol and ammonia-methane, and investigated their effect on engine performance and emissions. The experiments were conducted on a light-duty, single-cylinder, and spark-ignition four-stroke engine with an optically accessible cylinder head equipped with a port-fuel injection system. The results show that blending ethanol and methane with ammonia significantly improves its combustion characteristics due to the higher flame speed of the added components. Ammonia-ethanol blends produced reduced combustion duration, lower combustion instability, and higher engine efficiency compared to ammonia-methane blends due to the higher flame speed of ethanol. Additionally, ammonia-ethanol blends also produced higher NOx and CO2 emissions due to the higher in-cylinder temperature and lower H/C ratio. The study also applied high-speed natural flame luminosity imaging to observe the flame propagation speed for various fuel blending cases. The results found that ammonia-ethanol blends produced higher flame propagation speed than ammonia-methane blends.

Combustion Behaviors and Unregular Emission Characteristics in an Ammonia–Diesel Engine

Ammonia is considered one of the attractive alternatives for fossil fuels to realize carbon neutralization. However, low chemical reactivity limits its use in compression ignition (CI) engines. This study investigated dual-fuel combustion, involving the use of ammonia for port fuel injection (PFI) and diesel for direct injection (DI) in a heavy-duty engine. Unregular emissions, specifically HCN, were studied for the first time in an ammonia–diesel engine. The combustion and emission performance of the engine with pure diesel mode was also studied to reveal the influence on ammonia addition. The engine was consistently operated at a fixed condition of 0.556 MPa IMEP and 800 r/min. The findings reveal the successful achievement of stable dual-fuel combustion in the tested engine. The addition of ammonia led to delayed ignition and an extended combustion duration. Implementing early pilot injection timing (SOI1) strategies significantly improved ammonia combustion efficiency, elevating it from 74% to 89%. This enhancement could be attributed to the diesel injected during pilot injection, which facilitated ammonia decomposition. However, early pilot injection had adverse effects on emissions, including CO, THC, NOx, N2O, and HCN. Advancing the main injection timing (SOI2) within the early SOI1 strategies accelerated the oxidation processes for CO, THC, N2O, and HCN. Nevertheless, this adjustment resulted in increased thermal NOx emissions. The highest HCN emission detected in this study was 9.2 ppm. Chemical kinetics analysis indicated that HCN production occurred within the temperature range of 1000 K to 1750 K under fuel-lean conditions. Furthermore, H2CN played a significant role in HCN formation as temperatures increased. More HCN was formed by H2CN as temperature rose. Strategies such as increasing pilot injection fuel quantity, raising premixed gas intake temperature, or advancing combustion phases close to TDC could potentially reduce HCN emissions.

Evaluating the Environmental Impact of Ethanol Fuel: Particle Number Emissions in Flex-Fuel Vehicles

In Europe, the EURO 6 Light Duty emission standards, a consequence of Diesel vehicles, introduced limits for particle number (PN) of Gasoline Direct Injection (GDI) engines. Given the extremely small particles' concern about health effects, the same limits were set (6.0 x 1011 #/km) for diesel and GDI cars. In Brazil, the current phase for light vehicles of PROCONVE L6 enforced particulate matter (PM) mass emission standards for Diesel vehicles only, applying the limits of 25 mg/km for passenger cars and 30 mg/km for commercial vehicles. Similar to the European concern, even not considering the particle number (PN) emissions, future Brazilian phase L7, which is under study, considers a significant reduction in the limit of the particulate matter (PM) mass emission from current limits down to 6 mg/km for both Diesel and DI engines, for passenger and commercial vehicles. Aiming to contribute to hydrated ethanol fuel sustainability discussion compared to gasoline and for generating reference data regarding particle number (PN) emissions, which can be used for future emissions regulations of Flex-Fuel vehicles in the Brazilian market, this article explores particle number (PN) measurements of Flex-Fuel Vehicles equipped with direct injection (DI) and port fuel injection (PFI) engines, fueled with ethanol (E100) and gasohol (E22).

Experimental study on engine and emissions performance of renewable diesel methanol dual fuel (RMDF) combustion

Methanol (MeOH) and renewable diesel (RD) are being considered promising alternative fuels for the de-fossilization of internal combustion engines (ICE). This study provides an experimental investigation on the use of both fuels under dual-fuel combustion mode: port fuel injection (PFI) of MeOH and direct injection (DI) of RD. The combustion mode is labeled as RMDF (renewable diesel methanol dual fuel). The experiment was performed in a heavy-duty single-cylinder engine (SCE) equipped with combustion and emissions measurements and analysis for engine efficiency and emissions of soot and NOX (oxides of nitrogen). MeOH substitution rate, which is the mass ratio of injected MeOH fuel to total injected fuels of both MeOH and RD, was varied to study its effect on engine efficiency and emissions. Different MeOH substitutions were tested from low (6.9 bar gIMEP) to full (23.5 bar gIMEP) engine load conditions at a fixed engine speed of 1200 RPM.Test results showed that higher MeOH substitution rates can reduce NOX emissions effectively while improving engine thermal efficiency. However, a higher MeOH substitute rate can result in longer ignition delay at low load, and increased emissions of carbon monoxide (CO) and unburned hydrocarbon (UHC). Increased maximum pressure rise rate (MPRR) at high load condition was observed as the MeOH substitution rate increased. MPRR is not sensitive to the change in MeOH at low load condition. While ignition delay became longer at low load, it was shorter at high load as MeOH substitution rate increased. Overall, the results from this study suggest that RMDF can be considered as an option to achieve a cleaner and more efficient engine. However, further optimization of combustion designs and engine operating strategy need to be considered to improve combustion loss from RMDF emissions, possibly due to the lower reactivity of MeOH.

Recommendations for emission testing and control of exhaust particles from a late technology mono-fuel CNG vehicle

The current study characterizes sub-23nm volatile and non-volatile particle emissions from a late technology (Euro 6d-temp) port-fuel injection vehicle, operating with compressed natural gas (CNG) as the primary fuel and E10 gasoline, as a reserve fuel. In part of the testing, gasoline was replaced with alkylate fuel or was doped with an octane booster (MMT), to understand fuel impacts better. Alkylate use resulted to the lowest total particle number (TPN) emission levels, below that of the Euro 6 limit. Increased sensitivity to primary sampling temperature was observed for CNG due to the high H/C ratio that causes water condensation in the exhaust. A minimum sampling temperature of 70oC is recommended to avoid water particles in CNG operation. The study also assessed the potential of a particle filter (PF) in controlling total and solid CNG exhaust particles. Results indicate effective PF filtration of non-volatile and volatile particles, especially in the sub-23 nm size range. Gasoline and CNG tests with PF suggest TPN10 emissions in the order of 5 × 1011 p/km, below the Euro 6 and Euro 7 regulation limit. Adopting PF as part of the aftertreatment layout would be required for control of solid and total particle emissions from CNG vehicles.

Particulate emissions from gasoline vehicles using three different fuel injection technologies

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.

Evaluation and Simulation Analysis of Mixing Performance for Gas Fuel Direct Injection Engine under Multiple Working Conditions

Gas fuel direct injection (DI) technology can improve the control precision of the in-cylinder mixing and combustion process and effectively avoid volumetric efficiency reduction in a compressed natural gas (CNG) engine, which has been a tendency. However, compared with the port fuel injection (PFI) method, the former’s mixing path and duration are shortened greatly, which often leads to poor mixing uniformity. What is worse, the in-cylinder mixing performance would be seriously affected by engine working conditions, such as engine speed and load. Based on this situation, the fluid mechanics software FLUENT is used in this article, and the computational fluid dynamics (CFD) model of the injection and mixing process in a gas-fueled direct injection engine is established. A quantitative evaluation mechanism of the in-cylinder mixing performance of the CNG engine is proposed to explore the influencing rule of different engine speeds and loads on the mixing process and performance. The results indicate that phase space analysis can accurately reflect the characteristics of the mixture mixing process. The gas fuel mixture rapidly occupies the cylinder volume in the injection stage. During the transition stage, the gas fuel mixture is in a highly transient state. The diffusion stage is characterized by the continuous homogenization of the mixture. The in-cylinder mixing performance is linearly dependent on the engine’s working condition in the phase space.

Numerical analysis of performance, combustion, and emission characteristics of PFI gasoline, PFI CNG, and DI CNG engine

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.

Off-Cycle Emissions of Particle Number from Gasoline and DPF Diesel Passenger Cars in High-Load Conditions

To evaluate regulated gases and solid particle number (SPN) emissions in high-load off-cycle conditions, two diesel vehicles with a diesel particulate filter (DPF) and a urea selective catalytic reduction (SCR) system, respectively, and four gasoline port fuel injection (PFI) vehicles were tested with the worldwide light-duty test cycle, including an extra-high (Ex-hi) phase. All the tested vehicles were developed for the Japanese market and did not comply with the Ex-hi phase. All vehicles exhibited higher CO2 emissions in the Ex-hi phase than in low, the mid and high phases. Increased NOx and SPN10-23 emissions were observed with the DPF vehicle. These increased emissions were due to the occurrence of passive regeneration of the DPF, and the urea SCR system was stopped as a result. The small gasoline PFI cars showed increased CO and SPN emissions in the Ex-hi phase. These emissions were due to enrichment control, which occurred in a quite high load operation condition. The feature of higher emissions with enrichment control differed from that observed in a warming-up process in the cold-start mode. SPN23 increased mainly in the warming-up process, whereas SPN10-23 increased in the Ex-hi phase with enrichment control. Hybrid vehicles seem to have fewer opportunities to show the enrichment control due to motor assist.

Impacts on real-world extra cold start emissions: Fuel injection, powertrain, aftertreatment and ambient temperature

Vehicles emit substantial amounts of pollutants during start periods. Engine starts mainly occur in urban areas, causing serious harm to humans. To investigate the impacts on extra cold start emissions (ECSEs), eleven China 6 vehicles with various control technologies (fuel injection, powertrain, and aftertreatment) were monitored with a portable emission measurement system (PEMS) at different temperatures. For conventional internal combustion engine vehicles (ICEVs), the average ECSEs of CO2 increased by 24%, while the average ECSEs of NOx and particle number (PN) decreased by 38% and 39%, respectively, with air conditioning (AC) on. Gasoline direct injection (GDI) vehicles had 5% lower CO2 ECSEs, but 261% higher NOx ECSEs and 318% higher PN ECSEs than port fuel injection (PFI) vehicles at 23 °C. The average PN ECSEs were significantly reduced by gasoline particle filters (GPFs). The GPF filtration efficiency was higher in GDI than PFI vehicles due to particle size distribution. Hybrid electric vehicles (HEVs) generated excessive PN extra start emissions (ESEs), resulting in a 518% increase compared to ICEVs. The start times of the GDI-engine HEV accounted for 11% of the whole test time, but the proportion of PN ESEs relative to total emissions were 23%. Linear simulation based on the decrease in ECSEs with increasing temperature underestimated the PN ECSEs from PFI and GDI vehicles by 39% and 21%, respectively. For ICEVs, CO ECSEs varied with temperature in a U shape with a minimum at 27 °C; NOx ECSEs decreased as ambient temperature increased; PFI vehicles generated more PN ECSEs at 32 °C than GDI vehicles, stressing the significance of ECSEs at high temperature. These results are useful for improving emission models and assessing air pollution exposure in urban aeras.

Mixture Distribution in Spark Ignited Port Fuel Injection Engines: A Review

Abstract 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.

A Numerical Study on the Transient Injection Characteristics of Gas Fuel Injection Devices for Direct-Injection Engines

Natural gas has emerged as one of the preferred alternative fuels for vehicles owing to its advantages of abundant reserves, cleaner combustion and lower cost. At present, the gas supply methods for natural-gas engines are mainly port fuel injection (PFI) and direct injection (DI). The transient injection characteristics of a gas fuel injection device, as the terminal executive component of the PFI or DI mode, will directly affect the key performance of a gas fuel engine. Therefore, gas fuel injection devices have been selected as the research object of this paper, with a focus on the transient injection process. To explore the impacts of valve vibration amplitude, period, frequency and velocity on transient injection characteristics, one transient computational fluid dynamics (CFD) model for gas fuel injection devices was established. The findings thereof demonstrated that there is a linear relationship between the instantaneous mass flow rate and instantaneous lift during the vibration process. However, this relationship is somewhat impacted when the valve speed is high enough. A shorter valve vibration period tends to preclude a shorter period of flow-hysteresis fluctuation. The near-field pressure fluctuation at the throat of an injection device, caused by valve vibration, initiates flow fluctuation.

Experimental Study of Effect of Injection Timing on Port Fuel Injection Gasoline, Port Fuel Injection Compressed Natural Gas, and Direct Injection Compressed Natural Gas Engine Performance, Combustion, and Emissions Characteristics

Abstract Compressed natural gas (CNG) has gained popularity due to its wide availability, higher efficiency, and lower emissions compared to gasoline. However, the lower flame speed characteristics of CNG with conventional port injection reduce the CNG engine volumetric efficiency and power output. CNG's lower gas jet momentum during a low load operation creates a non-uniform air-fuel mixture that affects ignition and combustion quality. Direct injection of CNG with optimum injection timing is expected to improve volumetric efficiency, ignition quality, and combustion process. In this study, a comparative study on the effect of end-of-injection (EOI) timing on volumetric efficiency, thermal efficiency, combustion duration, and emissions was carried out in a single-cylinder port fuel injection (PFI) spark-ignition engine using gasoline and CNG, and direct injection (DI) spark ignition engine using CNG. The experiments were performed at two-part load operations of 20% and 40% throttle at 900 and 1500 rpm. Experimental results indicate that the PFI CNG engine is more influential in EOI timing than gasoline engines. The performance of the PFI CNG engine is improved when the injection occurs during the intake valve open period compared to the closed valve period with higher thermal efficiency, volumetric efficiency, and indicated mean effective power (IMEP). A shorter flame development angle and combustion duration were observed when EOI timing was in the open intake valve condition. DI CNG improved volumetric efficiency at advanced EOI timing compared to the PFI CNG engine. However, the combustion process is critically dependent on injection timing and air-fuel mixing duration. A three-dimensional computational fluid dynamics simulation was conducted to evaluate the effect of advanced and retarded EOI timing on DI CNG engine's in-cylinder turbulent kinetic energy development and in-cylinder equivalence ratio near the ignition point. An excess advanced EOI timing resulted in stratified rich and retarded EOI timing results in loss of turbulence energy, leading to a slightly rich and lean mixture for advanced and retarded EOI timing, respectively. Hence, an optimum EOI timing provides a conducive environment to initiate the combustion and flame front propagation. Further, advanced EOI timing was required at higher throttle opening and engine speed. The emissions in DI CNG were also greatly affected by EOI timing.

Design of an Optically Accessible Intake Manifold for Characterization of Liquid and Gaseous Jets in PFI Operating Conditions

The intake manifold and its components play a key role in the proper formation of air–fuel mixtures suitable for correct engine operation. In this article, starting from the original intake manifold design fitted to an optically accessible spark-ignited engine, a new solution was developed so as to allow the application of high-speed imaging of the fuel jet located between the runner and intake valves (Port Fuel Injection). To compare the two designs in terms of overall engine performance parameters such as volumetric efficiency, 0D/1D simulations were performed in motored conditions. Measurements at different crankshaft speed values were used for calibrating the intake line parameters and providing boundary conditions. Finite Element Analysis (FEM) was performed in SolidWorks to verify the structural strength of the new design when operating in the most critical conditions, i.e., boosted operation. As an overall conclusion, the results show that the new design guarantees a wider range of intake pressure values during the intake stroke, thus expanding the possible operative points. This can be obtained without compromising structural integrity, given that predicted safety factors were well above acceptable limits even for relatively high boost levels.

Atomization Process in Multi-hole Nozzle Spray for Port Fuel Injection (Fourth Report)

Atomization Process in Multi-hole Nozzle Spray for Port Fuel Injection (Fourth Report)