Browse Topic: Compressed natural gas

Items (142)

Measurement of Fuel Distribution in a Small PFI Spark-Ignition Engine Using Tracer PLIF

2020-01-0786

4/14/2020

The distribution of fuel-air mixture inside the engine cylinder strongly influences the combustion process. Planar laser-induced fluorescence (PLIF) is commonly used for fuel distribution measurement, however, it is mostly reported on moderate- to large-sized engines. In the present work, PLIF is applied to measure the fuel distribution inside the cylinder of a small, four-stroke, port-fuel-injection (PFI), spark-ignition engine with displacement volume of 110 cm3. Iso-octane was used as the base fuel, and 3-pentanone (15% by volume) was added as a fluorescent tracer in the base fuel. The effect of equivalence ratio, considering ϕ = 1.2, 1.0, and 0.8, on in-cylinder fuel distribution was studied with low throttle opening of 25% at 1200 rpm. PLIF images were recorded at different crank angle degrees during both intake and compression strokes over a swirl measurement plane located at the TDC position. It was found that the fuel stratification was present from intake to even late compression. Also, no significant change in fuel distribution patterns was noted at different crank angle degrees for a given operating condition. Instantaneous PLIF images of the fuel distribution at 330 CAD during compression also showed a considerable variation from one cycle to the next. As expected, the fluorescence signal intensity was increased with the increase in equivalence ratio. Results also showed that the fuel distribution was much more noticeable near the diametrically opposite location to the spark plug on the tested engine, and continued to exist till late compression (i.e. 330 CAD).

Garg, Shubham, Mittal, Mayank, Sahu, Srikrishna, Lakshminarasimhan, V

Effects of Piston Bowl Diameter on Combustion Characteristics of a Natural gas/Diesel Dual Fuel Engine

2019-01-217312/19/2019

Natural gas/diesel dual fuel engines have potential for a high thermal efficiency and low NOx emissions. However, they have the disadvantages of high unburned species emissions and lower thermal efficiencies at low loads (at low equivalence ratio). A way to solve this problem is to properly distribute the pilot fuel vapor in a natural-gas premixture. The combustion chamber geometry affects the combustion process since it influences the distribution of the pilot fuel vapor. This study investigates the influence of injection conditions and the piston bowl geometry on the performance and emissions of a dual fuel engine. Experiments were carried out using two pistons with different bowl diameters, 52 mm and 58 mm, at single-and two-stage diesel-fuel injection. The results show that the larger bowl provides lower hydrocarbon emissions at a lower equivalence ratio in the case of single-stage injection. For two-stage injection, the influence of the bowl diameter depends on the timing of the first injection. To elucidate the effects of pilot fuel distribution, computational fluid dynamics (CFD) calculations were conducted for non-reacting pilot fuel sprays under conditions equivalent to the experiments. As a result, the relative rich area of the pilot fuel in the case of the single injection in the large piston bowl do not impinge on the piston wall at the ignition timing of the experiment, which leads to higher heat release rate owing to the weak cooling effect.

Takizawa, Keigo, Tanaka, Hidetake, Horibe, Naoto, Ishiyama, Takuji, Sako, Takahiro

Effects of Engine Operating Condition and Fuel Property on Pre-Ignition Phenomenon in a Highly Boosted Premixed Natural Gas Engine

2019-01-215412/19/2019

The stochastic pre-ignition phenomenon plays a vital role to limit the further increasing BMEP for natural gas engines. In this study, the pre-ignition propensities were examined in a highly boosted premixed natural gas engine by various engine loads and air/fuel ratios, as well as different methane number (MN) altered by hydrogen addition. A proper pre-ignition evaluation method was proposed referring to intake temperature. Moreover, the limits of in-cylinder temperature and pressure for the onset of pre-ignition were estimated. The results show that both higher IMEP and richer mixture conditions readily lead to pre-ignition. The significant increases of pre-ignition frequency and heavy-knocking pre-ignition cycle present with lowering MN.

Chen, Run, Kuboyama, Tatsuya, Moriyoshi, Yasuo, Yasueda, Shinji, Doyen, Valerie, Martin, Jean-Baptiste

1D Numerical and Experimental Investigations of an Ultralean Pre-Chamber Engine

03-13-02-001211/19/2019

Abstract In recent years, lean-burn gasoline Spark-Ignition (SI) engines have been a major subject of investigations. With this solution, in fact, it is possible to simultaneously reduce NOx raw emissions and fuel consumption due to decreased heat losses, higher thermodynamic efficiency, and enhanced knock resistance. However, the real applicability of this technique is strongly limited by the increase in cyclic variation and the occurrence of misfire, which are typical for the combustion of homogeneous lean air/fuel mixtures. The employment of a Pre-Chamber (PC), in which the combustion begins before proceeding in the main combustion chamber, has already shown the capability of significantly extending the lean-burn limit. In this work, the potential of an ultralean PC SI engine for a decisive improvement of the thermal efficiency is presented by means of numerical and experimental analyses. The SI engine is experimentally investigated with and without the employment of the PC with the aim to analyze the real gain of this innovative combustion system. For both configurations, the engine is tested at various speeds, loads, and air-fuel ratios. A commercial gasoline fuel is directly injected into the Main Chamber (MC), while the PC is fed in a passive or active mode. Compressed Natural Gas (CNG) or Hydrogen (H2) is used in the actual case. A 1D model of the engine under study is implemented in a commercial modeling framework and is integrated with “in-house developed” sub-models for the simulation of the combustion and turbulence phenomena occurring in this unconventional engine. The numerical approach proves to reproduce the experimental data with good accuracy, without requiring any case-dependent tuning of the model constants. Both the numerical and experimental results show an improvement of the indicated thermal efficiency of the active PC, compared to the conventional ignition device, especially at high loads and low speeds. The injection of H2 into the PC leads to a significant benefit only with very lean mixtures. With the passive fueling of the PC, the lean-burn limit is less extended, with the consequent lower improvement potential for thermal efficiency.

Bozza, Fabio, De Bellis, Vincenzo, Tufano, Daniela, Malfi, Enrica, Müller, Christoph, Habermann, Knut

MISERLY POWER SYSTEMS

19TOFHP10_0210/1/2019

Engineers push engine, transmission technologies to turn off fuel usage. Commercial-truck powertrains are doing more with less. Engine developers are adding features that reduce fuel consumption, saving owners money while helping fleets reduce emissions. Digital technologies continue to transform commercial trucking as powertrain providers devise new ways to eke more from each drop of fuel. Engines now adapt to road conditions, adjusting power and shutting down some or all of the cylinders as demands change. Electric fans and maintenance monitoring now are being used to help keep engines running at maximum efficiency while using less fuel. Design teams also are refining technologies like start-stop and cylinder deactivation, working to make them smooth enough that drivers barely notice the systems are adapting to the environment.

Costlow, Terry

Methane Direct Injection in an Optical SI Engine - Comparison between Different Combustion Modes

2019-01-00831/15/2019

Natural gas, biogas, and biomethane are attractive fuels for compressed natural gas (CNG) engines because of their beneficial physical and chemical characteristics. This paper examines three combustion modes - homogeneous stoichiometric, homogeneous lean burn, and stratified combustion - in an optical single cylinder engine with a gas direct injection system operating with an injection pressure of 18 bar. The combustion process in each mode was characterized by indicated parameters, recording combustion images, and analysing combustion chemiluminescence emission spectra. Pure methane, which is the main component of CNG (up to 98%) or biomethane (> 98 %), was used as the fuel. Chemiluminescence emission spectrum analysis showed that OH* and CN* peaks appeared at their characteristic wavelengths in all three combustion modes. The peak of OH* and broadband CO2* intensities were strongly dependent on the air/fuel ratio conditions in the cylinder. Lower OH* and CO2* intensities were observed with lean air/fuel mixtures because under these conditions, more air was present, the combustion reactions were slower, and the cylinder pressure was higher. CN* was formed by the spark plasma and was detected over a particularly long period when using a dual coil ignition system. The intensities of the OH* and CN* signals correlated when using this ignition system. Combustion image analysis showed that the flame had a wrinkled boundary in stoichiometric and lean burn modes and was especially distorted in stratified mode. No yellow soot luminescence was observed during homogeneous combustion. However, the emission spectra and combustion images acquired during stratified combustion showed that soot formation occurred due to the presence of fuel-rich areas with inadequate mixing in the cylinder. The difficulty of maintaining stable fuel injection, achieving proper air/fuel mixing, and ensuring stable flame propagation in lean air/fuel mixtures increased cycle-to-cycle variations. However, the homogeneous lean burn and stratified combustion modes achieved significantly lower indicated specific fuel consumption values than stoichiometric combustion.

Melaika, Mindaugas, Andersson, Mats, Dahlander, Petter

Durability Improvement of Cylinder Head in Alternate Fuel Engines

2018-32-005510/30/2018

Alternate fuels like LPG and CNG are beneficial in terms of operating cost and emissions as well. They also contribute to reduce CO2 emissions. These gas fuels are known for its problems in engines including wear of parts. Cylinder head valve - seat wear is higher in gas engines. This paper discusses the experimental work on reduction of valve -seat wear in 3 wheeler engine. In the development of new higher power version of the gas engine valve-seat interface wear is observed. Effect of this wear on performance, leak and emissions were studied, qualitative measurements of valve temperatures were studied at different conditions with different fuels. Combustion gas and part temperatures are higher in gas engines. Simulation test cycle is developed for the wear test and various solutions to reduce wear at the valve - seat interface were evaluated. Cost effective solution is implemented with minimum changes in engine.

Thiruvallur Loganathan, Balasubramanian, Elumalai, Duraikkannan, Kumaraswamy, Phaneesh, Lakshminarasimhan, V

Study of Turbulent Entrainment Quasi-Dimensional Combustion Model for HCNG Engines with Variable Ignition Timings

2018-01-16879/10/2018

Presently, urban transportation highly depends on the fossil fuels, but its rapid fluctuating economic issues and environmental consequences impose the variegation of energy sources. Hydrogen enriched compressed natural gas (HCNG) engines offer the potential of higher brake thermal efficiency with low emissions, which also satisfies the strict pollutant emission standards. The two-zone turbulent entrainment quasi-dimensional combustion model is developed to predict the combustion process of spark-ignited hydrogen enriched compressed natural gas-fueled engines. The fundamentals of thermodynamic process, turbulent flame propagation model and other sub-models like laminar burning velocity, adiabatic temperature and ignition lag model are introduced for the better accuracy. The experiments have been conducted for three different fuels; pure CNG, 20% HCNG, and 40% HCNG blends under MAP of 105 kPa for various excess air ratios (λ) and ignition timing (θi). The three calibration coefficient of the model; Turbulent intensity coefficient C2, the Taylor length scale coefficient C3, and Ignition lag coefficient Cig are tuned to generate the pressure traces which closely resembled to experimental results. After comparing the numerical simulation results with the experiment’s outcomes it is found that the predictive accuracy of the presented model is quite impressive, and it is well accepted for the extremely fuel lean conditions where issues of bad combustion become serious.

Mehra, Roopesh Kumar, Ma, Fanhua, Hao, Duan, Juknelevičius, Romualdas

Improving Combustion and Emission Characteristics in Heavy-Duty Natural-Gas Engine by Using Pistons Enhancing Turbulence

2018-01-16859/10/2018

Compressed Natural Gas (CNG), because of its low cost, high H/C ratio, and high octane number, has great potential in automotive industry, especially for heavy-duty commercial vehicles. However, relative slow flame speed of natural gas leads to long combustion duration and low thermal efficiency and tends to cause knock combustion at high load, which will aggravate engine thermal load and reliability. Enhancing turbulence intensity in combustion chamber is an effective way to accelerate flame propagation speed and improve combustion performance. In this study, the flow simulations of several piston bowls with different inner-convex forms were carried out using three-dimensional computational fluid dynamics (3D-CFD) software CONVERGE. The numerical results showed the piston bowls with inner-convex could disturb the charge swirl motion and enhance turbulence of different intensity. A hexagram geometry bowl was proved to have the best function in strengthening turbulence intensity. Hence then the combustion processes were calculated based on the original and hexagram bowl. The simulation results suggested hexagram bowl enabled faster burning-rate than original bowl. Lastly, the comparative experiments were conducted at 1000 rpm and 6.5, 12 and 15 bar indicated mean effective pressure (IMEP) loads between the hexagram piston and original piston in the single-cylinder natural-gas engine. The test results indicated the hexagram piston presented approximate 1.8% higher indicated thermal efficiency (ITE) and total hydrocarbon (THC) emission reduced by 60% at 15 bar IMEP load lean burn condition compared to the original piston. However, at 6.5 bar IMEP load stoichiometric combustion, the hexagram piston exhibited about 1.5% lower ITE and poorer THC and nitrogen oxide (NOx) emission characteristics than the original piston, which required further optimization to improve in the future research.

Li, Fubai, Liu, Changpeng, Song, Heping, Wang, Zhi

Carbon Monoxide Emissions Model for Data Analytics in Internal Combustion Engine Applications Derived from Post-Flame Chemical Kinetics

2018-01-11534/3/2018

In this work, a new CO emissions formation model is developed based on the dynamics of a representative pool of radicals in the post-flame combustion gases. The ultimate target is the derivation of a kinetics-based CO model, formulated by a single differential equation, that can run very fast in any engine diagnostic/post-processing tool which analyzes in-cylinder processes in the framework of big data acquired at the engine test bench or during engine operation in the field. Specific objectives in the development of the current model are (i) inclusion of the effect of engine operating conditions on the CO emissions formation mechanism, (ii) ease of implementation in any diagnostic code/platform, (iii) fast running times toward real-time capability, and (iv) robustness. The presently developed CO model consists of a single Ordinary Differential Equation (ODE) that can be solved analytically, without the need of a stiff chemical kinetics solver. A characteristic parameter, which can be considered as a quenched CO index, is also derived to quantify the limits of maintaining the partial equilibrium of CO with the radical pool on the one hand and the quenching of the CO oxidation on the other hand. The model is used to study the quenching of CO oxidation under lean combustion conditions, as they currently appear in modern Spark Ignition (SI) and Diesel engines. As a first application, characteristic 2D maps of the quenched CO index are produced for a wide range of temperatures and cooling rates of the combustion gases under lean methane/air combustion conditions at various lambda values and pressures, revealing the relevant window of CO oxidation quenching. The CO model is then implemented into a quasi-dimensional, multi-zone combustion diagnostic tool for conventional homogeneous charge SI engines, developed by the authors. The combustion diagnostic tool is applied to a lean burn gas engine over a wide range of engine speeds at full load and contact lambda value. Qualitative results of the CO quenching process in the temperature-stratified burned gas are shown and explained. Finally, validation of the present CO model is performed comparing calculated CO emissions of the model against measured engine-out ones.

Bikas, Georgios, Michos, Konstantinos

Solid Particle Number and Ash Emissions from Heavy-Duty Natural Gas and Diesel w/SCRF Engines

2018-01-03624/3/2018

Solid and metallic ash particle number (PN) and particulate matter (PM) mass emission measurements were performed on a heavy-duty (HD) on-highway diesel engine and a compressed natural gas (CNG) engine. Measurements were conducted under transient engine operation that included the FTP, WHTC and RMC. Both engines were calibrated to meet CARB ultra low NOX emission target of 0.02 g/hp-hr, a 90% reduction from current emissions limit. The HD diesel engine final exhaust configuration included a number of aftertreatement sub-systems in addition to a selective catalytic reduction filter (SCRF). The stoichiometric CNG engine final configuration included a closed coupled Three Way Catalyst (ccTWC) and an under floor TWC (ufTWC). The aftertreatment systems for both engines were aged for a full useful life (FUL) of 435,000 miles, prior to emissions testing. PM mass emissions from both engines were comparable and well below the US EPA emissions standard. However, the CNG engine emitted a substantially higher number of solid particles, larger and smaller than 25 nm in diameter, compared to the number of particles emitted from the HD diesel engine for each of the three transient cycles tested. The CNG engine metallic ash particle number emission was also much higher than that of the diesel. The stringent solid particle number regulation in the EU and China will address the CNG particle number emission problem. However, in the USA there is no such regulation to specifically address particle number emissions, which is a short coming. Ultrafine PN emissions from engines is a health concern. Reducing solid particle number emissions from old and new CNG engines to a level comparable to that of a diesel with DPF is an important task that needs to be addressed by policy makers around the globe.

Khalek, Imad A., Badshah, Huzeifa, Premnath, Vinay, Brezny, Rasto

Numerical Investigation of Direct Gas Injection in an Optical Internal Combustion Engine

2018-01-0171

4/3/2018

Direct injection (DI) of compressed natural gas (CNG) is a promising technology to increase the indicated thermal efficiency of internal combustion engines (ICE) while reducing exhaust emissions and using a relatively low-cost fuel. However, design and analysis of DI-CNG engines are challenging because supersonic gas jet emerging from the DI injector results in a very complex in-cylinder flow field containing shocks and discontinuities affecting the fuel-air mixing. In this article, numerical simulations are used supported by validation to investigate the direct gas injection and its influence on the flow field and mixing in an optically accessible ICE. The simulation approach involves computation of the in-nozzle flow with highly accurate Large-Eddy Simulations, which are then used to obtain a mapped boundary condition. The boundary condition is applied in Unsteady Reynolds Averaged Navier-Stokes simulations of the engine to investigate the in-cylinder velocity and mixing fields. The velocity field has been measured using time-resolved stereoscopic Particle-Image Velocimetry in a running engine. The scalar field indicating the injected gas has been measured with Holographic Tomographic Interferometry. The cycle-to-cycle fluctuations in the measured velocity field are found to be high, presumably due to shocks and their reflections from cylinder walls. The proposed simulation approach can reasonably predict the ensemble-averaged velocity field. Yet, it cannot predict the wall-attached flow of the gas jet observed in the scalar field measurements. The impact of the gas jet from a centrally mounted injector on tumble motion and turbulent kinetic energy has been investigated. Gas injection at high injection pressures and lower engine speeds destroys the tumble flow generating high turbulence levels, which benefits the mixing. However, as a result, overall turbulence levels are reduced near the combustion top dead center compared to those without injection, which may lead to slower combustion in a fired engine.

Deshmukh, Abhishek Y., Falkenstein, Tobias, Pitsch, Heinz, Khosravi, Maziar, Bebber, David van, Klaas, Michael, Schroeder, Wolfgang

Characterization of Hollow Cone Gas Jets in the Context of Direct Gas Injection in Internal Combustion Engines

2018-01-02964/3/2018

Direct injection (DI) compressed natural gas (CNG) engines are emerging as a promising technology for highly efficient and low-emission engines. However, the design of DI systems for compressible gas is challenging due to supersonic flows and the occurrence of shocks. An outwardly opening poppet-type valve design is widely used for DI-CNG. The formation of a hollow cone gas jet resulting from this configuration, its subsequent collapse, and mixing is challenging to characterize using experimental methods. Therefore, numerical simulations can be helpful to understand the process and later to develop models for engine simulations. In this article, the results of high-fidelity large-eddy simulation (LES) of a stand-alone injector are discussed to understand the evolution of the hollow cone gas jet better. The hollow cone gas jet is characterized in terms of several parameters such as axial penetration length, maximum jet width, area of jet, volume of jet, and mixing in terms of the mass-weighted probability density of the injected gas within the jet volume. Different grid resolutions have been used to study the effect on the gas jet behavior as well as mixing. The power-law scaling of the temporal evolution of the axial penetration length, maximal width, and area of jet is compared with the previously published literature for a similar injector. The applicability of different turbulence models commonly used in computationally cheaper Unsteady Reynolds-Averaged Navier-Stokes (URANS) simulations is investigated. Both LES and URANS simulations overpredict the axial penetration length because of the initial nonlinear behavior of the jet evolution. The transient needle opening has been found to impact initial stages of the gas jet formation and is responsible for the linear jet evolution observed in experiments. Moreover, the initial condition has a strong influence on later jet evolution in case of fixed needle simulations.

Deshmukh, Abhishek Y., Vishwanathan, Giridar, Bode, Mathis, Pitsch, Heinz, Khosravi, Maziar, Bebber, David van

An Analysis of Dual-Fuel Combustion of Diesel with Compressed Natural Gas in a Single-Cylinder Engine

2018-01-02484/3/2018

The recent increase in natural gas availability has made compressed natural gas (CNG) an option for fueling the transportation sector of the United States economy. In particular, CNG is advantageous in dual-fuel operation alongside ultra low sulfur diesel (ULSD) for compression ignition (CI) engines. This work investigates the usage of natural gas mixtures at varying Energy Substitution Rates (ESRs) within a high compression ratio single-cylinder CI engine, including performance and heat release modeling of dual-fuel combustion. Results demonstrate the differing behavior of utilizing CNG at various substitution rates. In particular, low ESRs (0-18%) find that operation is not too dissimilar from that of neat ULSD, moderate ESRs (40-60%) show that combustion begins to change but significant modifications to engine operation (i.e., ULSD injection timing) are not required, and high ESRs (75-85%) demonstrate relatively large changes to ULSD injection behavior in order to achieve optimized operation. In addition, this work examines the differing engine emissions profiles with varying ESRs, highlighting the potential for CNG usage to lower Particulate Matter (PM) emissions, while alternatively increasing or decreasing NOx production through changes to in-cylinder temperatures and heat release rates. Dual-fuel combustion is noted for significant decreases in combustion efficiency, and a rise in emissions of methane and non-methane hydrocarbons, showcasing an increasing likelihood of flame quenching from cooler in-cylinder temperatures. This lowered combustion efficiency also affects brake-specific engine efficiency, requiring slightly more fuel energy to be expended as ESR increases in comparison to operation with neat ULSD. However, this may be offset from an operational perspective due to the lowered costs of CNG as a fuel. Finally, there may exist the potential to achieve high thermal efficiencies just below peak engine operation for relatively large substitution rates of CNG without potentially increasing NOx emissions over operation with neat ULSD.

Mattson, Jonathan M. S., Langness, Chenaniah, Depcik, Christopher

Comparison of Engine Operational Modes with Respect to Compression Ignition Engine Knock

2018-01-02194/3/2018

Diesel knock and ringing combustion in compression ignition (CI) engines are largely an unavoidable phenomenon and are partially related to the overall effectiveness of the fuel injection process. Modern electronic fuel injection systems have been effective at reducing the intensity of knock in CI engines, largely through optimization of fuel injection timing, as well as higher operating pressures that promote enhanced fuel and air mixing. In this effort, a single-cylinder CI engine was tested under a number of different combustion strategies, including a comparison of mechanical and electronic injection systems, increasing fuel injection pressures for biodiesel fuels, and the usage of dual-fuel combustion with compressed natural gas (CNG). Using in-cylinder pressure traces and engine operational data, the difference in injection mechanisms, fuel preparation, and their effects on knock intensity is clearly illustrated. This allows a means of comparison across multiple engine combustion modes, including mechanical vs. electronic injection, injection of various fuels through a common injection system, and standard operation against dual-fuel operation. In particular, the effect of higher injection pressures and fuel flow rates on reducing knock in some cases is highlighted. In addition, cyclic variability in the severity of ringing combustion appears to be a function of the ability of the fuel system to re-pressurize between engine cycles. This offers a potential means to provide for diagnosis of engine fuel pressurization system deficiencies through variability in ringing combustion, even if these deficiencies would not be discernible from normal measured operational characteristics.

Mattson, Jonathan M. S., Depcik, Christopher

J2406_201802 (Current)2/12/2018

Truck and Bus Powertrain Committee

Liquefied Natural Gas (LNG) Vehicle Metering and Dispensing Systems - Truck and Bus

J2645_201802 (Current)2/12/2018

Truck and Bus Powertrain Committee

Real World Fleet Test to Determine the Impact of Low Viscosity Engine Oils from Heavy-Duty CNG and Diesel Buses - Part I: Fuel Consumption

2017-01-235310/8/2017

One of the most interesting alternatives to reduce friction losses in the internal combustion engines is the use of low viscosity engine oils. Recently, a new engine oil category focused fuel economy, has been released in North America encouraging the use of these oils in the heavy-duty vehicles’ segment. This paper presents the results of a comparative test where the differences in fuel consumption given by the use of these oils are shown. The test included 48 buses of the urban public fleet of the city of Valencia, Spain. The selected vehicles were of four different bus models, three of them fueled with diesel and the other one with compressed natural gas (CNG). Buses’ fuel consumption was calculated on a daily basis from refueling and GPS mileage. After three oil drain intervals (ODI), the buses using low viscosity engine oils presented a noticeable fuel consumption reduction. These results bear out the suitability of these oils to palliate engine inefficiencies.

Tormos, Bernardo, Ramirez, Leonardo, Miró, Guillermo, Pérez, Tomás

Port Fuel Injection of CNG for Downsized 1-Liter 3-Cylinder Turbocharged Engine with High Efficiency

2017-01-227510/8/2017

In order to meet increasingly stringent emission regulations and reduce fuel consumption, development of modern powertrain is becoming more complicated, combining many advanced technologies. Gasoline engine downsizing is already established as a proven technology to reduce vehicle fleet CO2 emissions. Compressed natural gas (CNG) offers increased potential to further reduce both tailpipe CO2 and other regulated exhaust gas emissions without compromising driving performance. In this study, a turbocharged CNG port fuel injection (PFI) engine was developed based on gasoline version. Making most use of positive fuel properties of CNG, the paper quantifies the performance characteristics of downsized CNG engine considering reduced knock sensitivity, adaption of compression ratio and combustion efficiency. While peak cylinder pressure was controlled below 120 bar, peak torque 180Nm, same level as gasoline variant, was realized from 3000rpm. The results achieved from the test engine whilst operating with CNG are also compared to measurements from turbocharged gasoline PFI and turbocharged gasoline direct injection (TGDI).With adapted compression ratio for CNG operation, effective combustion efficiency is over 38%, which is even higher than TGDI version. Finally, it was concluded that compared to gasoline application, operation with CNG will lead to 24.2% CO2 emission reduction as well as 46.4% mileage-specific fuel cost saving.

Yang, Chen, li, Weixin, Yin, Jiandong, Shen, Yuan

Development of CNG/Diesel Dual-Compatible Engine Oil for Heavy-Duty Trucks in Thailand

2017-01-235010/8/2017

In Thailand, most heavy-duty trucks were equipped with diesel engine, while a small portion was equipped with compressed natural gas (CNG) engine. However, in the past few years the number of CNG fuel trucks in Thailand has increased significantly due to the cheaper cost of CNG. In general, the emphasis of heavy-duty diesel engine oil performance is on piston cleanliness and soot handling properties, while thermal and anti-oxidation properties are most critical for CNG engine oil performance. For truck fleet owners who operate both types of trucks, using the inappropriate oil that is not fit-for-purpose can adversely affect engine performance and reduce engine service lifespan under prolonged usage. A novel CNG/diesel engine oil was developed to meet both JASO DH-2 heavy-duty diesel engine oil performance and CNG engine oil performance. The candidate formulation was proved adequately fit for practical use regarding to thermal and anti-oxidation properties. Engine durability tests were conducted for 4-liter and 8-liter of diesel engines with 8-liter of CNG engine. Top Groove Fill (TGF), Weighted Total Demerit (WTD) as piston cleanliness and used-oil properties were measured. It was further demonstrated that the Komatsu hot tube deposit bench test correlated well with 8-liter diesel engine durability test. A field-trial was conducted on commercially operated diesel and CNG trucks in Thailand. The developed SAE 15W-40 viscosity grade engine oil exhibited no harm in both diesel and CNG trucks throughout the entire field-trial.

Wongtaewan, Chalermwut, Wongjareonpanit, Umaporn, Sivara, Komkrit, Hashimoto, Ken, Nakamura, Yoichiro

Real World Fleet Test to Determine the Impact of Lower Viscosity Engine Oils from Heavy-Duty CNG and Diesel Buses. Part II: Oil Performance

2017-01-235110/8/2017

Low viscosity engine oils are considered a feasible solution for improving fuel economy in internal combustion engines (ICE). So, the aim of this study was to verify experimentally the performance of low viscosity engine oils regarding their degradation process and possible related engine wear, since the use of low viscosity engine oils could imply higher degradation rates and/or unwanted wear performance. Potential higher wear could result in a reduction in life cycle for the ICE, and higher degradation rates would be translated in a reduction of the oil drain period, both of them non-desired effects. In addition, currently limited data are available regarding “real-world” performance of low viscosity engine oils in a real service fleet. In this particular case, there were included out-of-the European Automobile Manufacturers' Association (ACEA) oil specifications in terms of HTHS dynamic viscosity, where low viscosity was considered (3.0 mPa·s), making this test highly interesting for industry. On this test, 49 buses were monitored using a deep and extensive oil analysis program, comprising two engine technologies (Diesel and CNG), four engine types and three different lubricants, two of them low viscosity engine oils and other two as a reference baseline, during an oil drain period of 30000 km, taking between 5 to 10 samples per bus. For every sample, a broad list of thermo-physical and chemical properties were measured, and specially engine wear was quantified using ICP-OES, in order to detect abnormal wear patterns in the engine. Results indicate that oil performance and wear effects do not show abnormal patterns due to use of low viscosity engine oils, even some parameters obtain a better performance because of higher quality formulation.

Tormos, Bernardo, Miró, Guillermo, Ramirez, Leonardo, Pérez, Tomás

Evaluating Different Measures to Improve the Numerical Simulation of the Mixture Formation in a Spark-Ignition CNG-DI-Engine

2017-01-05673/28/2017

Compressed Natural Gas (CNG) is a promising alternative fuel for internal combustion engines as its combustion is fuel-efficient and lean in carbon dioxide compared to gasoline. The high octane number of methane gives rise to significant increase of the thermodynamic efficiency due to higher possible compression ratios. In order to use this potential, new stratified mixture formation concepts for CNG are investigated by means of numerical fluid simulations. For decades RANS methods have been the industry standard to model three-dimensional flows. Indeed, there are well-known deficiencies of the widely used eddy viscosity turbulence models based on the applied Boussinesq hypothesis. Reynolds stress turbulence models as well as scale resolving simulation approaches can be appealing alternative choices since they offer higher accuracy. However, due to their large computing effort, they are still mostly impractical for the daily use in industrial product development processes. A more suitable solution seems to be the application of an explicit algebraic Reynolds stress (EARSM) turbulence model based on a non-linear relation between the Reynolds stresses and the mean strain-rate. This allows a better prediction of various flow effects in the simulations. In the presented work the direct injection of CNG has been simulated by means of commercial RANS-based CFD using various turbulence models. The simulation set-up includes the discretization of one cylinder and part of the centrally mounted injector geometry. High pressure ratios are present in between the rail and the cylinder resulting in a supersonic gas jet emerging from the injector and mixing into the surrounding air. Mass transfer in between both components is modeled by a passive scalar transport equation based on the gradient diffusion hypothesis using a constant global turbulent Schmidt number. It is shown in this work that the capturing of anisotropic turbulence effects is crucial for the correct modeling of the mixture formation because turbulent diffusion is dominant in the mixing layer of supersonic gas jets. Overall an explicit algebraic Reynolds stress model predicts more pronounced mixing and shows better agreement with experimental data than the commonly used eddy viscosity turbulence models.

Twellmeyer, Andrea, Kopple, Fabian, Weigand, Bernhard

Influence of Binary CNG Substitute Composition on the Prediction of Burn Rate, Engine Knock and Cycle-to-Cycle Variations

2017-01-05183/28/2017

Since 0D/1D-simulations of natural gas spark ignition engines use model theories similar to gasoline engines, the impact of changing fuel characteristics needs to be taken into consideration in order to obtain results of higher quality. For this goal, this paper proposes some approaches that consider the influence of binary fuel mixtures such as methane with up to 40 mol-% of ethane, propane, n-butane or hydrogen on laminar flame speed and knock behavior. To quantify these influences, reaction kinetics calculations are carried out in a wide range of the engine operation conditions. Obtained results are used to update and extend existing sub-models. The model quality is validated by comparing measured burn rates with simulation results. The benefit of the new sub-models are utilized by predicting the influence the fuel takes on engine operating limits in terms of knocking and lean misfire limits, the latter being determined by using a cycle-to-cycle variation model.

Hann, Sebastian, Urban, Lukas, Grill, Michael, Bargende, Michael

J1616_201703 (Current)3/6/2017

Compressed Natural Gas (CNG) is a practical automotive fuel, with advantages and disadvantages when compared to gasoline. Large quantities of natural gas are available in North America. It has a higher octane number rating, produces low exhaust emissions, no evaporative emissions and can cost less on an equivalent energy basis than other fuels. Natural gas is normally compressed from 20 684 to 24 821 kPa (3000 to 3600 psig) to increase its energy density thereby reducing its on-board vehicle storage volume for a given range and payload. CNG can also be made from liquefied natural gas by elevating its pressure and vaporizing it to a gas. Once converted it is referred to LCNG. The properties of natural gas are influenced by: (1) source of supply i.e. field, composition or impurities; (2) the processing of natural gas by the production and transmission companies; (3) the regional gas supply, storage, and demand balancing done by distribution companies often in concert with pipeline companies to maintain uninterrupted service throughout the year, e.g., peak shaving with propane-air (see U.S. Bureau of Mines Publication 503); and (4) dispensing site maintenance characteristics i.e. filtration and drying. The Coordinating Research Council (CRC) has published the results of a national compressed natural gas vehicle fuel survey. Information on the properties of distribution system natural gas and its variability has been included in Figure 1, 2, and 3, and can be found in CRC Report No. PC-2-12. Composition can vary hourly under certain operating conditions in certain areas of the country. Thus the data should generally be considered representative for the areas mentioned with due consideration for local variation. Natural gases transported throughout the U. S. are not subject to uniform national standards. Under federal government rules covering interstate sales of natural gas, the U. S. Federal Energy Regulatory Commission (FERC) adjudicates tariffs, placing economic and technical requirements upon natural gases entering interstate commerce. In 2006, FERC issued a policy statement advising stakeholders that: 1 Only natural gas quality and interchangeability specifications contained in FERC-approved gas tariffs can be enforced; 2 Pipeline tariff provisions on gas quality and interchangeability need to be flexible to allow pipelines to balance safety and reliability concerns; 3 Pipelines and their customers should develop gas quality and interchangeability specifications based on technical requirements; 4 In negotiating technically-based solutions, pipelines and their customers are strongly encouraged to use the Natural Gas Council Plus (NGC+) Interim Guidelines…as a common reference point for resolving gas quality and interchangeability issues; and 5 To the extent pipelines and their customers cannot resolve disputes over gas quality and interchangeability, those disputes can be brought before FERC to be resolved on a case-by-case basis…1 The NGC+ Interim Guidelines call for natural gas specifications that include: 1 A range of plus or minus 4% Wobbe number variation from local historical average gas, or alternatively, established adjustment or target gas for the service territory, subject to: a Maximum Wobbe number limit: 1400 b Maximum higher heating value limit: 1110 Btu/scf 2 Additional composition maximum limits: a Maximum butanes+: 1.5 mole percent b Maximum total inerts: 4 mole percent 3 EXCEPTION: Service territories with demonstrated experience with supplies exceeding these Wobbe, higher heating value and/or compositional limits may continue to use supplies conforming to this experience as long as it does not unduly contribute to safety and utilization problems of end use equipment.2 While the Interim Guidelines provide only guidance for the setting of tariff limits on gas quality, experience has shown that in most cases the Wobbe and higher heating value limits are used in interstate tariffs. Since the bulk of U. S. sales of natural gas fall under FERC jurisdiction, this means that the Interim Guideline limits represent, in most cases, the limits that apply to natural gases received by distribution systems. Intrastate natural gas sales, by contrast, are not within FERC jurisdiction, but customers including utilities receiving gases from both intrastate and interstate sources, for practical purposes, generally receive natural gas that meets the Interim Guidelines. The NGC+ Interim Guidelines address combustion issues associated with natural gases. Separately, FERC considered condensable hydrocarbons in response to a second paper from NGC+.3 No specific actions were recommended by FERC in response to the NGC+ recommendations from this report, which basically recommended translation of historical condensable hydrocarbon experience into more general phase diagram-depicted “cricondentherm hydrocarbon dew point” (CHDP) criteria for higher hydrocarbon mixtures. CHDP criteria help ensure that natural gases of various compositions remain in gaseous state at all operating pressures and all reasonable ambient temperatures. Natural gas is comprised chiefly of methane (generally 88 to 96 mole percent) with the balance being a decreasing proportion of proportion of higher hydrocarbon alkanes such as ethane, propane, and butane. It can also contain nitrogen, water, carbon dioxide, oxygen, sulfur compounds and trace amounts of lubricating oil. At the retail outlet a warning agent, or odorant, is likely present in natural gas. Experience with natural gas vehicles has grown considerably. Fleet and ongoing in-use applications provide a foundation for characterizing gas composition factors that will help to understand gas quality effects on vehicle and overall performance and may cause fundamental operational problems for natural gas vehicles (NGVs). Water content and other corrosion precursors, heavier hydrocarbons, which may condense within the fuel container, particulate matter, oil, and energy content all need to be considered. Condensable hydrocarbons (liquid state) are also of concern in NGV equipment degradation.

Fuels and Lubricants TC 7 Fuels Committee

Fuel Tank for Liquefied Natural Gas

TBMG-261601/1/2017

NASA’s Marshall Space Flight Center has developed a new composite vessel technology that is suitable for use as a liquefied natural gas (LNG) fuel storage tank for alternative fuel vehicles. This technology uses an improved composite over-wrapped technology to produce a pressure vessel that is simple to use, robust, and capable of withstanding high pressures. It is also lightweight and low cost. This technology shows great potential to help the United States and other countries move toward a cleaner environment while allowing for efficient use of a more natural fuel in many different applications.

Composite Pressure Vessel Including Crack Arresting Barrier

TBMG-2601712/1/2016

NASA’s Marshall Space Flight Center innovators have developed several new designs and methods of fabrication for composite and composite-overwrapped tank vessels that help significantly improve their structural integrity against impact, abrasion, harsh environments, and fire. Several embodiments of this technology portfolio also enable production of composite tanks capable of transporting liquefied natural gas or other cryogenic liquids. These innovations are applicable to important aerospace needs, including propulsion systems, as well as new and growing fields such as natural gas transportation.

Heavily Downsized Demonstrator Engine Optimised for CNG Operation

2016-01-236310/17/2016

The complexity of modern powertrain development is demonstrated by the combination of requirements to meet future emission regulations and test procedures such as Real Driving Emissions (RDE), reduction of fuel consumption and CO2 emissions as well as customer expectations for good driving performance. Gasoline engine downsizing is already established as a proven technology to reduce automotive fleet CO2 emissions. Additionally, alternative fuels such as natural gas, offer the potential to significantly reduce both tailpipe CO2 and other regulated exhaust gas emissions without compromising driving performance and driving range. This paper presents results showing how the positive fuel properties of natural gas can be fully utilised in a heavily downsized engine. The engine has been modified to cope with the significantly higher mechanical and thermal loads when operating at high specific outputs on compressed natural gas (CNG). In this study, peak cylinder pressures of up to 180 bar and specific power output levels of 110 kW/litre have been realised. It is also shown that having cylinder components specific to natural gas can yield significant reductions in fuel consumption, and, in conjunction with a variable geometry turbine, a port-fuelled CNG engine can achieve impressive low-speed torque (27 bar BMEP at 1500 rpm) and good transient response characteristics. The results achieved from the test engine whilst operating on CNG are compared to measurements from the baseline, gasoline-fueled, direction injection (GDI) engine. The potential CO2 savings offered by this heavily downsized CNG engine, of up to 50% at peak power and 20-40% for the drive-cycle region (including real driving emissions (RDE) testing), are presented and discussed.

Hall, Jonathan, Bassett, Mike, Hibberd, Benjamin, Streng, Simon

Hydrocarbon Speciation in Blended Gasoline-Natural Gas Operation on a Spark-Ignition Engine

2016-01-216910/17/2016

The high octane rating and more plentiful domestic supply of natural gas make it an excellent alternative to gasoline. Recent studies have shown that using natural gas in dual fuel engines provides one possible strategy for leveraging the advantages of both natural gas and gasoline. In particular, such engines been able to improve overall engine efficiencies and load capacity when they leverage direct injection of the natural gas fuel. While the benefits of these engine concepts are still being explored, differences in fuel composition, combustion process and in-cylinder mixing could lead to dramatically different emissions which can substantially impact the effectiveness of the engine’s exhaust aftertreatment system. In order to explore this topic, this study examined the variations in speciated hydrocarbon emissions which occur for different fuel blends of E10 and compressed natural gas and for different fuel injection strategies on a spark-ignition engine. Results indicate that hydrocarbon emissions are clearly impacted by the base fuel structure and that differences in the underlying fuel chemistry can produce significant variations (over 300%) in the emissions of various hydrocarbon species. Injection strategy plays a role in the amount of mixing achieved and as such impacts emissions, but fuel structure is a much more significant factor. By using 50-75% percent compressed natural gas (CNG) at the lower load points, total methane and non-methane emissions could be reduced by up to 37% without any significant drop in engine efficiency. At the higher load points, usage of 100% CNG is more advantageous due to the knock constraints.

Hall, Carrie M., Sevik, James, Pamminger, Michael, Wallner, Thomas

Analysis of a Dual-Fuel Combustion Engine Fueled with Diesel Fuel and CNG in Transient Operating Conditions

2016-01-2305

10/17/2016

The paper presents the thermodynamic analysis of the engine supplied with small and large diesel fuel doses while increasing natural gas quantity. The paper presents changes in the combustion process thermodynamic indexes and changes in the exhaust gas emissions for dynamically increased share of the gaseous fuel. The cylinder pressure history was subject to thermodynamic analysis, . based on which the mean indicated pressure, the heat release rate, the quantity of heat released as well as the pressure rate increase after self-ignition were determined. These parameters were also referred to the subsequent engine operation cycles by specifying the scope of the change per cycle. The relationship between the engine load and the start, the center and the end of combustion while increasing the gas amount supplied to the cylinder was indicated. The presented analysis of the results indicates significant impact of the changes in the supplied gas amount on the engine operating indexes and exhaust emissions. The conducted tests made it possible to confirm that significant cooling of the cylinder (determined by the constant temperature of exhaust gas) does not allow combustion of a dual-fuel mixture during dynamic change of the engine fueling. It was shown that there is a relation between the thermal history of the cylinder (steady state conditions), the engine fueling rate and the possibility of combustion of a diesel-methane mixture.