Ducted Fuel Injection: A New Approach for Lowering Soot Emissions from Direct-Injection Engines.
Abstract not provided.
Mueller, Charles J.↗
SEARCH · Search NASA
Results for “direct injection”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Multicycle large-eddy simulations of a direct-injection hydrogen-fueled optical engine
Hydrogen (H 2 ) is a carbon-free chemical energy carrier and one promising solution for achieving effective decarbonization of the transportation sector, particularly for internal combustion engines (ICEs). With a focus on ICEs, and compared to port-fuel injection, direct injection (DI) of gaseous H 2 during the compression stroke offers potential advantages, which include backfire avoidance and reduction of preignition occurrence. In these last two decades, much research, experimental and numerical, has been devoted to understanding H 2 's mixing and combustion processes in ICEs. Computational fluid dynamics modeling efforts commonly rely on unsteady Reynolds-averaged Navier Stokes (URANS) turbulence frameworks, mostly due to their computational affordability. However, many authors have pointed out the opportunity to perform large-eddy simulations (LESs) to investigate the cyclic variability of H 2 engines and assess potential advantages of using LES in place of URANS, especially for lean operation. This study addresses this knowledge gap and presents a computational fluid dynamics (CFD) study of the H 2 DI process in an optical engine operating at relatively low tumble conditions, using multicycle LESs. In conclusion, the manuscript presents a thorough validation of the results against experimental data available from the literature as well as direct comparison with URANS, demonstrating the feasibility of multicycle LESs for CFD modeling of DI H 2 -fueled ICEs.
Direct injection↗
Particulate Matter Sampling and Volatile Organic Compound Removal for Characterization of Spark Ignited Direct Injection Engine Emissions
More stringent emissions regulations are continually being proposed to mitigate adverse human health and environmental impacts of internal combustion. With that in mind, it has been proposed that vehicular particulate matter (PM) emissions should be regulated based on particle number in addition to particle mass. One aspect of this project is to study different sample handling methods for number based aerosol measurements, specifically, two different methods for removing volatile organic compounds (VOCs) from an aerosol sample. One method is a Dekati Thermodenuder (TD) and the other is an evaporative chamber/diluter (EvCh). These sample handling methods have been implemented for this project in an engine test cell built around a direct injection spark ignited (DISI) engine. The engine was designed for stoichiometric, homogeneous combustion. Direct injection is of particular interest for improved fuel efficiency but this comes with the production of a significant amount of (PM) and may therefore be subject to the proposed number based regulation. Another aspect of this project is to characterize PM from this engine in terms of particle number and composition. The first interesting observation is that PM number distributions, acquired using a TSI SMPS, have a large accumulation mode (30-294 nm) but a very small nuclei mode (8-30 nm). This is understood to represent a lack of condensation particles meaning that neither the exhaust conditions nor the sample handling conditions are conducive to condensation. This lack of nuclei mode does not, however, represent a lack of VOCs in the sample. It has been observed, using mass spectral analysis (limited to PM>50 nm), that PM from the DISI engine has approximately 40% organic content through varying operating conditions. This begs the question of how effective different sample handling methods are at removing these VOCs. For one specific operating condition, called Cold Start, the un-treated PM was 40% organic. The TD reduced this by 7% while the EvCh reduced it by 13%. For other operating conditions, PM treated for volatile removal actually exhibited an increase in organic fraction on the order of 5%. This addition appears to be sensitive to the gaseous hydrocarbon concentrations in the exhaust although a precise correlation has not yet been derived. It has been concluded that VOCs are tightly bound to the PM carbon core and thus are not effectively removed by either treatment method.
Environmental Molecular Sciences Laboratory↗
PERFORMANCE, EFFICIENCY AND EMISSIONS EVALUATION OF GASOLINE PORT-FUEL INJECTION, NATURAL GAS DIRECT INJECTION AND BLENDED OPERATION
The need to further reduce fuel consumption and decrease the output of emissions — in order to be within future emissions legislation — is still an ongoing effort for the development of internal combustion engines. Natural gas is a fossil fuel which is comprised mostly of methane and makes it very attractive for use in internal combustion engines because of its higher knock resistance and higher molar hydrogen-to-carbon ratio compared to gasoline. The current paper compares the combustion and emissions behavior of the test engine being operated on either a representative U.S. market gasoline or natural gas. Moreover, specific in-cylinder blend ratios with gasoline and natural gas were also investigated at part-load and wide open throttle conditions. The dilution tolerance for part-load operation was investigated by adding cooled exhaust gas recirculation. The engine used for these investigations was a single cylinder research engine for light duty application which is equipped with two separate fuel systems. Gasoline was injected into the intake port; natural gas was injected directly into the cylinder to overcome the power density loss usually connected with port fuel injection of natural gas. Injecting natural gas directly into the cylinder reduced both ignition delay and combustion duration of the combustion process compared to the injection of gasoline into the intake port. Injecting natural gas and gasoline simultaneously resulted in a higher dilution tolerance compared to operation on one of the fuels alone. Significantly higher net indicated mean effective pressure and indicated thermal efficiency were achieved when natural gas was directly injected after intake valve closing at wide open throttle, compared to an injection while the intake valves were still open. In general it was shown that the blend ratio and the start of injection need to be varied depending on load and dilution level in order to operate the engine with the highest efficiency or highest load.
Advanced Combustion↗
Influence of Injector Location on Part-Load Performance Characteristics of Natural Gas Direct-Injection in a Spark Ignition Engine
Interest in natural gas as an alternative fuel source to petroleum fuels for light-duty vehicle applications has increased due to its domestic availability and stable price compared to gasoline. With its higher hydrogen-to-carbon ratio, natural gas has the potential to reduce engine out carbon dioxide emissions, which has shown to be a strong greenhouse gas contributor. For part-load conditions, the lower flame speeds of natural gas can lead to an increased duration in the inflammation process with traditional port-injection. Direct-injection of natural gas can increase in-cylinder turbulence and has the potential to reduce problems typically associated with port-injection of natural gas, such as lower flame speeds and poor dilution tolerance. A study was designed and executed to investigate the effects of direct-injection of natural gas at part-load conditions. Steady-state tests were performed on a single-cylinder research engine representative of current gasoline direct-injection engines. Tests were performed with direct-injection in the central and side location. The start of injection was varied under stoichiometric conditions in order to study the effects on the mixture formation process. In addition, exhaust gas recirculation was introduced at select conditions in order to investigate the dilution tolerance. Relevant combustion metrics were then analyzed for each scenario. Experimental results suggest that regardless of the injector location, varying the start of injection has a strong impact on the mixture formation process. Delaying the start of injection from 300 to 120°CA BTDC can reduce the early flame development process by nearly 15°CA. While injecting into the cylinder after the intake valves have closed has shown to produce the fastest combustion process, this does not necessarily lead to the highest efficiency, due to increases in pumping and wall heat losses. When comparing the two injection configurations, the side location shows the best performance in terms of combustion metrics and efficiencies. For both systems, part-load dilution tolerance is affected by the injection timing, due to the induced turbulence from the gaseous injection event. CFD simulation results have shown that there is a fundamental difference in how the two injection locations affect the mixture formation process. Delayed injection timing increases the turbulence level in the cylinder at the time of the spark, but reduces the available time for proper mixing. Side injection delivers a gaseous jet that interacts more effectively with the intake induced flow field, and this improves the engine performance in terms of efficiency.
Sevik, James↗
INVESTIGATION INTO REACTIVITY SEPARATION BETWEEN DIRECT INJECTED AND PREMIXED FUELS IN RCCI COMBUSTION MODE
This experimental study focuses on the effects of the reactivity separation between the port injected fuel and the direct injection fuel, the amount of external-cooled exhaust gas recirculation (EGR), and the direct injection timing of the high reactivity fuel on Reactivity Controlled Compression Ignition (RCCI) combustion. The experiments were conducted on a lightduty, single-cylinder diesel engine with a production GM/Isuzu engine head and piston and a retrofitted port fuel injection system. The global charge-mass equivalence ratio, ϕ′, was fixed at 0.32 throughout all of the experiments. To investigate the effects of the fuel reactivity separation, different Primary Reference Fuels (PRF) were port injected, with the PRF number varying from 50 to 90. To investigate the effects of EGR, an EGR range of 0 to 55% was used. To investigate the effects of the injection timing, an injection timing window of -65 to -45 degrees ATDC was chosen. The results indicate that there are several tradeoffs. First, decreasing the port injected fuel reactivity (increasing the PRF number) delays combustion phasing, decreases the combustion efficiency by up to 9%, increases the gross indicated thermal efficiency up to 22%, enhances the combustion sensitivity to the direct injection timing, and slightly increases the UHC, CO, and NOx emissions. Second, increasing the EGR percentage delays combustion phasing, lowers the peak heat release rate, and lowers the NOx emissions. The combustion efficiency first increases and then decreases with EGR percentage for high reactivity fuels (low PRF number), but only decreases for low reactivity fuels. Finally, delaying the injection timing advances combustion phasing and increases the combustion efficiency, but decreases the gross indicated thermal efficiency and increases the NOx emissions. Across all of the experiments, delays in CA50 increase the gross indicated thermal efficiency and decrease the combustion efficiency, which represents an inherent tradeoff for RCCI combustion on a lightduty engine.
Yan, Ziming↗
Influence of Compression Ratio on High Load Performance and Knock Behavior for Gasoline Port-Fuel Injection, Natural Gas Direct Injection and Blended Operation in a Spark Ignition Engine
Natural Gas (NG) is an alternative fuel which has attracted a lot of attention recently, in particular in the US due to shale gas availability. The higher hydrogen-to-carbon (H/C) ratio, compared to gasoline, allows for decreasing carbon dioxide emissions throughout the entire engine map. Furthermore, the high knock resistance of NG allows increasing the efficiency at high engine loads compared to fuels with lower knock resistance. NG direct injection (DI) allows for fuel to be added after intake valve closing (IVC) resulting in an increase in power density compared to an injection before IVC. Steady-state engine tests were performed on a single-cylinder research engine equipped with gasoline (E10) port-fuel injection (PFI) and NG DI to allow for in-cylinder blending of both fuels. Knock investigations were performed at two discrete compression ratios (CR), 10.5 and 12.5. Operating conditions span mid-load, wide-open-throttle and boosted conditions, depending on the knock response of the fuel blend. Blended operation was performed using E10 gasoline and NG. An additional gasoline type fuel (E85) with higher knock resistance than E10 was used as a high-octane reference fuel, since the octane rating of E10-NG fuel blends is unknown. Spark timing was varied at different loads under stoichiometric conditions in order to study the knock response as well as the effects on performance and efficiency. As anticipated, results suggest that the knock resistance can be increased significantly by increasing the NG amount. Comparing the engine operation with the least knock resistant fuel, E10 PFI, and the fuel blend with the highest knock resistance, 75% NG DI, shows an increase in indicated mean effective pressure of about 9 bar at CR 12.5. The usage of reference fuels with known knock characteristics allowed an assessment of knock characteristic of intermediate E10-NG blend levels. Mathematical correlations were developed allowing characterizing the occurrence of knocking combustion by using the Livengood-Wu knock integral. For most of the fueling strategies and operating conditions, the mathematical correlations show good agreement when compared to experimental data.
combustion↗
CFD unified approach under Eulerian–Lagrangian framework for methanol and gasoline direct injection sprays in evaporative and flash boiling conditions
Innovative synthetic fuels for advanced propulsion systems, such as methanol and ammonia, and synthetic blended fuels (E00, E10, and E30), known for their high volatility, are often injected directly into combustion chambers. It follows that Eulerian–Lagrangian spray models need to accurately capture the spray collapse as a consequence of flash boiling onset and be capable of proficiently handling the preferential evaporation of multi-component fuels in evaporative scenarios. So, we performed the assessment of an Eulerian–Lagrangian CFD code for simulating methanol and E00 gasoline blend sprays in both early and late injection conditions involving flash boiling conditions and preferential evaporation. The adoption of an effervescent breakup model and of a non-equilibrium phase transition model for the discrete phase allows the adoption of a setup that is almost completely free from specific constant tuning, especially for what concerns the breakup model. We validated the simulations using experimental PLV maps of methanol and E00 sprays issued from the ECN Spray M injector. The results highlight a significantly different morphology of the methanol spray compared to the E00 one under late injection conditions. Under stratified combustion, low-volatile fuels are likely to be ignited first, and the flame propagates toward the high-volatile fuels. In conclusion, the spray collapse was also correctly reproduced, inducing the presence of a low-pressure zone and modifying the spray morphology.
E00↗
Evaluation of Spray and Combustion Models for Simulating Dilute Combustion in a Direct-Injection Spark-Ignition Engine
Dilute combustion in spark-ignition engines has the potential to improve thermal efficiency by mitigating knock and by reducing throttling and wall heat losses. However, ignition and combustion processes can become unstable for dilute operation due to a lowered laminar flame speed, resulting in excessive cycle-to-cycle variability (CCV) of the combustion process. To compensate for the slower combustion in less reactive mixtures, a modified intake port geometry can be employed to generate a strong tumble flow in the cylinder and elevate turbulence levels around the spark plug, thereby promoting a faster transition to turbulent deflagration. Consequently, optimizing combustion chamber geometry and operating strategy is crucial to maximizing the benefits of using dilute combustion with enhanced in-cylinder turbulence across a wide range of operating conditions. Computational fluid dynamics (CFD) simulations can be utilized for virtual engine optimization tasks, but this would require the models to be truly predictive regarding the impact of changes to the engine design and operational parameters.In this study, multicycle large-eddy simulations (LES) are performed for a direct-injection spark-ignition engine to investigate the model performance in predicting engine combustion characteristics with respect to changes in the intake configuration. A tumble plate that blocks the lower part of the intake port inlet is used to vary the tumble. A set of CFD models that have been recently developed are employed, which takes into account the drag of nonspherical droplets, flash-boiling behavior of liquid sprays, spray-wall interaction, surrogate formulation of a research-grade E10 gasoline, and fast chemical kinetic solvers. Simulation results are compared to experimental engine data in terms of cylinder pressure, apparent heat release rate, mass fraction burned timing, and flame images. It is found that LES employing the state-of-the-art CFD models are capable of properly predicting the spray processes and reproducing the measured mean cylinder pressure for the case with the tumble plate. On the other hand, the LES over-predicts the combustion rate during the early combustion stage and under-estimates the CCV, and these discrepancies become larger when the tumble plate is removed.
computational fluid dynamics simulation↗
Multidimensional Modeling of Mixture Formation in a Hydrogen-Fueled Heavy-Duty Optical Engine With Direct Injection
Hydrogen (H 2 ), as a carbon-free fuel, is considered as one of the most promising solutions to reduce the carbon footprint of hard-to-decarbonize energy and transportation sectors. As such, hydrogen-fueled internal combustion engines (H 2 ICEs) have recently been receiving increasing attention, particularly in applications such as on-road/off-road heavy-duty transport and combined heat and power. The direct injection (DI) of gaseous hydrogen into the combustion chamber offers great potential for achieving high power density and high engine efficiency, while mitigating the risk of backfire and reducing pre-ignition. However, the numerical simulation of H 2 DI system remains a formidable challenge associated with the high computational cost of reproducing compressible supersonic flow and shocks in narrow injector passages and in near-nozzle regions. In general, there is a lack of well-established and validated practices for the modeling of high-pressure H 2 DI in large-bore engines. Here, to this end, this study focuses on computational fluid dynamics (CFD) modeling of the mixture formation process in a heavy-duty optical engine employing a medium-pressure H 2 DI system. Both large eddy simulations (LES) and Reynolds Averaged Navier–Stokes (RANS) simulations are performed and evaluated against optical data. Gaseous hydrogen is injected into the combustion chamber via a centrally located outward opening hollow-cone injector at a pressure of 40 bar. Simulations are carried out for two injection timings, namely, −120 and −60 °CA. The numerical predictions for H 2 distribution in different horizontal and vertical planes during the compression stroke are systematically compared against optical data obtained through planar laser-induced fluorescence (PLIF) measurements. Overall, the LES approach using the Dynamic Structure model is found to have good predictive capabilities for the early jet penetration in terms of length and shape, as well as the later H 2 distributions. However, the unsteady RANS approach with the renormalization group $k - ϵ$ model, which is widely used by industry to model heavy-duty ICEs, significantly underpredicts the H 2 mixing, even at similar mesh resolution to that used in LES. These results indicate that there is a need for the improvement of mixing submodels within the RANS approach when applied to H 2 DI simulations.
LES↗
Performance of direct injected propane and gasoline in a high stroke-to-bore ratio SI engine: Pathways to diesel efficiency parity with ultra low soot
This work explores pathways to achieve diesel-like, high-efficiency combustion with stoichiometric 3-way catalyst compatible combustion in a single-cylinder spark ignition (SI) research engine. A unique high stroke-to-bore engine design (1.5:1) with cooled exhaust gas recirculation (EGR) and high compression ratio ( r c ) was used to improve engine efficiency by up to 30% compared with a production turbocharged gasoline direct injection spark ignition engine. Engine experiments were conducted with both 91 RON E10 gasoline and liquified petroleum gas (LPG) (i.e. autogas) and were compared to legacy gasoline data on the production engine. Geometric compression ratio ( r c ) of 13.3:1 was used for both fuels with additional experiments at 16.8:1 for LPG only. Measurements of exhaust soot particle size and number concentrations were made with both fuels. Significant reduction in soot particles across the whole particle size range were achieved with LPG due to the elimination of in-cylinder liquid films. The effects of EGR, late intake valve closing (IVC) and fuel characteristics were investigated through their effects on efficiency, combustion stability and soot production. Results of 47% gross thermal efficiency, and 45% net thermal efficiency at stoichiometric engine operation, at up to 17 bar IMEP and 2000 r/min with 16.8:1 r c were achieved with LPG. Estimated brake efficiency values were compared to a contemporary medium duty diesel engine illustrating the benefits of the chosen path for achieving diesel efficiency parity.
33 ADVANCED PROPULSION SYSTEMS↗
Fuel Property Effects on Knock Propensity and Thermal Efficiency in a Direct-Injection Spark-Ignition Engine
Engine knock remains one of the major barriers to further improvement in thermal efficiency of Direct-Injection Spark-Ignition (DISI) engines. While Research Octane Number and Motor Octane Number are often used as standard rating methods for knock resistance of fuels, the impacts of other fuel properties on knock propensity in modern engines such as heat of vaporization (HoV) and laminar flame speed (LFS) require better understanding in order to co-optimize fuels and engine designs to achieve higher thermal efficiency and lower CO2 emission. In the present study, computational fluid dynamics (CFD) is used to model a boosted DISI engine with a focus on knock prediction and fuel property effects. A level-set G-equation model is employed to capture turbulent premixed combustion, and is coupled with a transported Livengood-Wu (L-W) integral approach to predict autoignition in the unburnt region. A criterion associated with the L-W integral is developed to accurately predict knock onset and knock-limited spark-advance. This model is then applied to a sensitivity analysis of HoV and LFS on knock tendency and thermal efficiency. The pressure-temperature trajectory framework is applied and extended to study the fuel effects on auto-ignition process in the engine. An existing efficiency-based merit function, which is derived from experiments for boosted SI engines, is evaluated and improved based on the current CFD results.
DISI↗
Bowl geometry effects on turbulent flow structure in a direct injection diesel engine.
Abstract not provided.
Busch, Stephen↗
Investigation of the Impact of Fuel Properties on Particulate Number Emission of a Modern Gasoline Direct Injection Engine
Gasoline Direct Injection (GDI) has become the preferred technology for spark-ignition engines resulting in greater specific power output and lower fuel consumption, and consequently reduction in CO2 emission. However, GDI engines face a substantial challenge in meeting new and future emission limits, especially the stringent particle number (PN) emissions recently introduced in Europe and China. Studies have shown that the fuel used by a vehicle has a significant impact on engine out emissions. In this study, nine fuels with varying chemical composition and physical properties were tested on a modern turbo-charged side-mounted GDI engine with design changes to reduce particulate emissions. The fuels tested included four fuels meeting US certification requirements; two fuels meeting European certification requirements; and one fuel meeting China 6 certification requirements being proposed at the time of this work. Two risk safeguard fuels (RSG), representing the properties of worst case market fuels in Europe and China, were also included. The particle number concentration of the solid particulates was measured in the engine-out exhaust flow at steady state engine operations with load and speed sweeps, and semi-transient load steps. The test results showed a factor of 6 PN emission difference among all certification fuels tested. Combined with detailed fuel analyses, this study evaluated important factors (such as oxygenates, carbon chain length and thermo-physical properties) that cause PN emissions which were not included in PMI index. A linear regression was performed to develop a PN predictive model which showed improved fitting quality than using PMI.
33 ADVANCED PROPULSION SYSTEMS↗
Experimental and Numerical Study on the Effect of Nitric Oxide on Autoignition and Knock in a Direct-Injection Spark-Ignition Engine
We report Nitric Oxide (NO) can significantly influence the autoignition reactivity and this can affect knock limits in conventional stoichiometric SI engines. Previous studies also revealed that the role of NO changes with fuel type. Fuels with high RON (Research Octane Number) and high Octane Sensitivity (S = RON – MON (Motor Octane Number)) exhibited monotonically retarding knocklimited combustion phasing (KL-CA50) with increasing NO. In contrast, for a high-RON, low-S fuel, the addition of NO initially resulted in a strongly retarded KL-CA50 but beyond the certain amount of NO, KL-CA50 advanced again. The current study focuses on same high-RON, low-S Alkylate fuel to better understand the mechanisms responsible for the reversal in the effect of NO on KLCA50 beyond a certain amount of NO. Experiments were conducted to measure the responses of KL-CA50 and trace-autoignition CA50, the latter being indicative of CA50 at which end-gas autoignition starts to become measurable from the apparent heat-release rate. Chemical-kinetics simulations were conducted to reveal the role of NO for end-gas autoignition, with a specific focus on sequential autoignition in a thermally stratified end-gas. The simulation results reveal that the magnitude of low-temperature heat release (LTHR) generally increases with NO. However, the relative importance of NO for enhancing LTHR diminishes when the LTHR inherent to a fuel’s chemistry is strong, such as at lower temperatures in a thermal boundary layer. This rendered more uniform LTHR within a hypothetical thermal boundary and led to a more sequential (i.e. slower) autoignition event. It was also revealed that a change in compression ratio influences the importance of intermediate-temperature heat release (ITHR) due to changes of the temperature-pressure history of the end-gas. Together with the condition where end-gas autoignition occurs more sequentially, the shorter time spent in LTHR and ITHR regime can counter the increase in autoignition reactivity at high NO levels and allow KLCA50 to advance
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
European Lean Gasoline Direct Injection Vehicle Benchmark
Lean Gasoline Direct Injection (LGDI) combustion is a promising technical path for achieving significant improvements in fuel efficiency while meeting future emissions requirements. Though Stoichiometric Gasoline Direct Injection (SGDI) technology is commercially available in a few vehicles on the American market, LGDI vehicles are not, but can be found in Europe. Oak Ridge National Laboratory (ORNL) obtained a European BMW 1-series fitted with a 2.0l LGDI engine. The vehicle was instrumented and commissioned on a chassis dynamometer. The engine and after-treatment performance and emissions were characterized over US drive cycles (Federal Test Procedure (FTP), the Highway Fuel Economy Test (HFET), and US06 Supplemental Federal Test Procedure (US06)) and steady state mappings. The vehicle micro hybrid features (engine stop-start and intelligent alternator) were benchmarked as well during the course of that study. The data was analyzed to quantify the benefits and drawbacks of the lean gasoline direct injection and micro hybrid technologies from a fuel economy and emissions perspectives with respect to the US market. Additionally that data will be formatted to develop, substantiate, and exercise vehicle simulations with conventional and advanced powertrains.
02 PETROLEUM↗