Natural Gas Direct Injection Research Articles

Investigation on online perception method of gas injection characteristics for the high-pressure natural gas direct injection engine

To realize the online perception of the gas injection process for high-pressure natural gas direct injection engines. This paper presents an innovative perception method for gas injection characteristics. The injection characteristics are divided into time characteristics and quantify characteristics. The gas inlet pressure is used to be the sensing signal. Firstly, time characteristics are highlighted on the frequency domain signal by short-time Fourier transform, and all kinds of time characteristics are defined in the time domain. To improve the real-time performance of the algorithm, the mean instantaneous frequency (MIF) was selected as the representative of the frequency at each moment to reduce the dimension of the time–frequency signal. Based on the zero and local maximum points of the MIF signal, a recognition method of the injector time characteristics is proposed. The neural network is used to build the prediction model of the quantified characteristics. The results show that: In all the ranges of the injector working conditions, the error of the time characteristics is less than 5%. The root mean square error of the injection mass is 2.68 mg, and the regression coefficient between the predicted value and the measured value is 0.99878. The method proposed in this paper has relatively high accuracy.

Experimental study on the two-phase fuel transient injection characteristics of the high-pressure natural gas and diesel co-direct injection engine

In this paper, an innovative fuel injection rate measurement methodology for the natural gas and diesel co-direct injection injector was designed to study the dual-fuel injection characteristics for a high-pressure natural gas direct injection engine. The results indicate that the injection mass shows two different upward trends as the energizing time (ET) increases, and it appears more sensitive to the length of ET when it is short. The gas injection duration is affected by both the injection pressure and ambient pressure under the same ET, thus any increase in either will significantly increase the injection duration, resulting in a pronounced increase in gas injection mass. The process of diesel pilot injection has a remarkable effect on the gas injection rate. According to the actual engine working condition, provided that the pilot diesel ET is 0.8 ms, the gas injection mass reaches the minimum value when the split time is about 0.8 ms, meanwhile, it reaches the maximum value when the split time is about 0.2 ms or 2 ms. The results of this study can provide an accurate database for the performance of the injector and accurate fuel injection boundary conditions for the combustion process in the engine cylinder.

Numerical Study on the Combustion and Emission Characteristics of a Direct Injection Natural Gas Engine Ignited by Diesel/N-Butanol Blends

Numerical Study on the Combustion and Emission Characteristics of a Direct Injection Natural Gas Engine Ignited by Diesel/N-Butanol Blends

Large-Eddy Simulation of a Natural Gas Direct Injection Spark Ignition Engine with Different Injection Timings

Large-Eddy Simulation of a Natural Gas Direct Injection Spark Ignition Engine with Different Injection Timings

Experimental Study on Entrainment Characteristics of High-Pressure Methane Free Jet.

Entrainment occurs during the high-pressure gas jet process, which is crucial for a natural gas direct injection engine. This study presents an experimental investigation on the high-pressure methane jet from one single-hole injector and proposes a method to obtain the entrainment mass flow rate based on kinetic energy conservation. The entrainment is related to three variables, i.e., spring plate moving distance Δx, gas jet mass at the nozzle outlet mn, and gas jet velocity u1. A spring-set test rig is built to measure the spring plate moving distance Δx, and the schlieren method is adopted to test the gas jet velocity u1 based on a constant-volume bomb (CVB) optical test rig; finally, the weight method is used to obtain the methane gas jet mass at the nozzle outlet mn. This combined measuring method is verified to be valid in the near field to the nozzle. The results show that the methane jet mass flow rate gradually increases along the jet direction and has a two-zone entrainment process. Zone I: near field (Lr < 10), the methane jet mass flow rate linearly increases up to the maximum; in the nozzle exit field (Lr < 1), it is conserved, and no entrainment occurs. Zone II: far field (Lr ≥ 10), the jet mass flow rate maintains the maximum, and the entrainment becomes saturated with a saturation value larger than the initial value at the nozzle outlet. The entrainment rate experiences three stages, linearly increasing in stage I and early stage II but not in late stage II and stage III. The methane injection pressure causes great effects on the mass flow rate and entrainment. As the injection pressure increases, the methane jet mass flow rate increases linearly, but the entrainment rate decreases.

Performance and emissions of a pilot ignited direct injection natural gas engine operating at slightly premixed combustion mode

Due to the increased attention on energy saving and carbon emission reduction, the research on techniques for the improvement of engine efficiency has become more attractive. Slightly premixed combustion mode has been considered as an effective method for raising thermal efficiency. In this paper, the performance and emissions of a pilot ignited direct injection natural gas engine operating at slightly premixed combustion mode were evaluated by experiments and compared to those of mixing-limited combustion mode. The results indicated that brake thermal efficiency could be improved by up to 1.1% to 3.6% when slightly premixed combustion mode is utilized at different engine loads. At BMEP higher than 6.5 bar, adoption of slightly premixed combustion mode could cause NOx emissions to rise by more than 7.3% while at BMEP lower than 13.0 bar, significant increases in THC emissions may be accompanied. It is also revealed that using slightly premixed combustion mode could reduce CO emissions by more than 35.2% at BMEP higher than 6.5 bar and reduce soot emissions by more than 55.8% at all engine loads. Moreover, the effects of the injection parameters are highly dependent on engine load, which means that the trends for thermal efficiency and emissions are different at different engine loads.

Experimental Research of High-Pressure Methane Pulse Jet and Premixed Ignition Combustion Performance of a Direct Injection Injector

Natural gas (NG) direct injection (DI) technology benefits the engine with high efficiency and clean emissions, and the high-pressure gas fuel injection process causes crucial effects on the combustion. This study presents an optical experimental investigation on the high-pressure methane single-hole direct injection and premixed ignition combustion based on a visualization cuboid constant volume bomb (CVB) test rig. The experimental results show that the methane jet process is divided into two stages. The methane gas jet travels at a faster speed during the unstable stage I than that during the stable stage II. The injection pressure causes more influence on both the jet penetration distance and the jet cone area during stage II. The methane jet premixed flame is a stable flame with a nearly spherical shape, and its equivalent radius linearly increases. The methane jet premixed flame area also increases while the flame stretch rate declines. The methane jet premixed flame velocity rises as both the standing time and equivalent ratio increase. The methane jet premixed flame is a partial premixed flame, and the peak of the methane jet premixed flame occurs at greater equivalence ratio ϕ, i.e., ϕ &gt; 2. As the injection pressure rises, the jet premixed flame equivalent radius increases, and the flame velocity linearly increases. The higher the methane injection pressure, the faster the jet premixed flame velocity.

Knocking characteristics of a high pressure direct injection natural gas engine operating in stratified combustion mode

Abstract Knocking becomes an increasingly important issue in direct injection natural gas engines with the application of new combustion modes. In this article, the knocking characteristics of natural gas engine operating in stratified combustion mode were studied with the aid of cylinder pressure oscillations and combustion parameters. The results indicated that knocking tendency will be stronger when operating in stratified combustion mode. The first to the fourth circumferential modes and the first radial mode are the featured modes for knocking behavior, while knocking is more serious when the duration of 10–50% of total energy released is shorter.

Effects of injection strategy on the knocking behavior of a pilot ignited direct injection natural gas engine

Pilot ignited direct injection natural gas engines have become a research focus due to the high thermal efficiency and low emissions. However, when stratified combustion mode is adopted, more attention should be paid to the knocking behavior. In this paper, the effects of injection strategy on the knocking behavior of a pilot ignited direct injection natural gas engine have been studied. The results indicated that the knocking intensity will be increased at advanced natural gas injection timing, delayed diesel injection timing and raised injection pressure. The three major resonance modes that dominate the pressure oscillations are the first circumferential mode, the third circumferential mode and the first radial mode. Advancing natural gas injection has negative effects on cyclic variations of indicated mean effective pressure while have negligible effects on the cyclic variations of combustion duration. After correlation analysis of parameters, it was found that knocking behavior is highly correlated with maximum heat release rate, combustion duration and maximum combustion pressure, whereas has weak correlations with combustion phasing and cyclic variations.

Heat release rate and emissions regimes of stratified pilot-ignited direct-injection natural gas combustion.

Natural gas (NG) is an attractive fuel for heavy-duty internal combustion engines because of its potential for reduced CO2, particulate, and NOX emissions and lower cost of ownership. Pilot-ignited direct-injected NG (PIDING) combustion uses a small pilot injection of diesel to ignite a main direct injection of NG. Recent studies have demonstrated that increased NG premixing is a viable strategy to increase PIDING indicated efficiency and further reduce particulate and CO emissions while maintaining low CH4 emissions. However, it is unclear how the combustion strategies relate to one another, or where they fit within the continuum of NG stratification. The objective of this work is to present a systematic evaluation of pilot combustion, NG combustion, and emissions behavior of stratified-premixed PIDING combustion modes that span from fully-premixed to non-premixed conditions. A sweep of the relative injection timing, , of NG and pilot diesel was performed in a heavy-duty PIDING engine with = 140-220 bar, = 0.47-0.71, and a constant NG energy fraction of 94%. Apparent heat release rate and emissions analyses identified interactions between the pilot fuel and NG, and qualitatively characterized the impact of NG stratification on combustion and emissions. Changes in the resulted in six distinct PIDING combustion regimes, for all considered injection pressures and equivalence ratios: (i) RIT-insensitive premixed, (ii) stratified-premixed (early-cycle injection), (iii) NG jet impingement transition, (iv) stratified-premixed (late-cycle injection), (v) variable premixed fraction, and (vi) minimally-premixed. Parametric definitions for the bounds of each regime of combustion were valid for the wide range of and investigated, and are expected to be relevant for other PIDING engines, as previously identified regimes agree with those identified here. This conceptual framework encompasses and validates the findings of previous stratified PIDING investigations, including optimal ranges of operation that provide significantly increased efficiency and lower emissions of incomplete combustion products.

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

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

Environmental performance of four different heavy-duty propulsion technologies using Life Cycle Assessment

The goal of this study is to perform an environmental analysis using the Life Cycle Assessment methodology to compare different technologies for heavy-duty trucks: Diesel, Diesel Hybrid, Spark-Ignited Natural Gas, High-Pressure Direct Injection Natural Gas. The analysis considers five impact categories: climate change, particulate matter, ozone photochemical formation, terrestrial eutrophication and acidification. This paper also contains a Total Cost of Ownership analysis.The main results reveal a reduction between 5 and 6% of Greenhouse Gases for alternative propulsion technologies. Natural gas trucks show a considerable reduction (40–50%) compared to conventional diesel in terms of terrestrial eutrophication and acidification, besides, for particulate matter and photochemical ozone formation, there are also minor reductions (10%).The economic analysis indicates that diesel is an attractive alternative, despite its poor environmental behaviour, and natural gas trucks do not seem to be as economically competitive as diesel. Diesel hybrid results show a not good option neither economically nor environmentally.

Experimental investigation of the performance and emissions of a dual-injection SI engine with natural gas direct injection plus gasoline port injection under lean-burn conditions

Conventional gasoline SI engines have low efficiency and poor lean burn characteristics at lower loads. The objective of this study is to improve the combustion and emission performance of gasoline SI engines under lean burn conditions through dual-injection mode with gasoline port injection and natural gas direct injection(GPI + NDI). In this work, total fuel energy is kept constant for all investigated test points. The sole gasoline mode with port injection is used as the baseline and compared with the GPI + NDI mode. The results show that the proposed GPI + NDI mode provides stable and promising performance. In particular, the GPI + NDI mode achieves stable combustion with COVIMEP lower than 1.5 under the condition of λ = 1.4 where the sole gasoline mixture cannot stably combustion, which broadens the lean burn limit of the gasoline engine at low load. Compared with pure gasoline mode, GPI + NDI mode with appropriate RCNG and direct injection timing can increase efficiency by 0.7 and 0.94 percentage points at λ = 1 and 1.2, and BSFC drops by 3.1% and 3.6%. HC continues to decrease with the increase of RCNG. CO emissions at λ = 1 decrease first and then increases with the increase of RCNG, and when λ is higher than 1.2, CO emissions reach extremely low levels. Furthermore, there is a significant effect on the limitation of the total particle number(TPN)with the increase of RCNG. When λ = 1 and 1.2, the TPN has a downward trend with the RCNG increases. Since there is enough oxygen to ensure the complete oxidation of the particles, TPN is not sensitive to changes in RCNG at λ = 1.4.

Effect of the HPDI and PPCI Combustion Modes of Direct-Injection Natural Gas Engine on Combustion and Emissions

Natural gas (NG) engines have very broad application prospects. The pilot-ignited NG diesel engine can be organized into two combustion modes according to the sequence of oil and gas injection: (1) High-pressure direct injection, where NG is mainly diffused combustion; and (2) partially premixed compression ignition, where NG is mainly premixed combustion. In this study, we used CONVERGE to explore the influence of the NG injection timing on the distribution of the mixture equivalence ratio, ignition characteristics, thermal efficiency, emission, and combustion reaction rate under the two combustion modes. We also used a multi-step soot model to analyze the particle mass and quantity. We showed herein that the NG injection timing significantly affects the mixture distribution in the cylinder, thereby consequently affecting the combustion process. Both very early and very late injection times were not conducive to NG combustion. In addition, the mass, quantity, and diameter of the soot produced by diffusion combustion were larger than those produced with premixed combustion.

Investigation of the Combustion Kinetics Process in a High-Pressure Direct Injection Natural Gas Marine Engine

The present work was supported by the National Natural Science Foundation of China (Grant No. 91941102) and the High-Tech Ship Research of the Ministry of Industry and Information Technology of the People’s Republic of China (Grant No. MC-201501-D01-03).

Energy optimization of a micro-CHP engine using 1-D and 3-D modeling

This research focused on utilizing numerical simulation tools to improve the performance of a micro-CHP engine. The engine was developed at West Virginia University by screening candidate technologies and implementing those which were balanced between practicality and cost. The engine was a 34-cc, two-stroke engine which was modified to operate on low-pressure direct injection of natural gas combined with resonant intake and exhaust systems. This engine served as a baseline engine design. A 1-D simulation was developed and trained based on the baseline engine geometry and experimental data collected from laboratory experiments. After verifying the 1D model with measured data from the baseline configuration, a genetic algorithm approach was used to optimize the exhaust resonator design such that the fuel efficiency was maximized. Based on simulation outcomes, a new exhaust resonator was fabricated and tested. The experimental results showed an 8.3% improvement in brake thermal efficiency (BTE) compared to the baseline design. The test results of the optimized exhaust design were used in a 3-D CFD cold flow model to optimize the spark plug location to exploit charge stratification. The 3-D simulations suggested an alternative spark plug location, which was then applied on the engine and improved results were verified with additional experimental operation. The experimental results showed relative increase in BTE of 5.7% and a 4% decrease in total unburnt fuel compared to the original spark location.

Quantitative 1-D LIBS measurements of fuel concentration in natural gas jets at high ambient pressure

Fuel concentration information is critical to the development of high-efficiency combustion system of direct-injection natural gas engines. In this study, a one-dimensional (1-D) measurement approach based on laser induced breakdown spectroscopy (LIBS) is developed to quantitatively measure 1-D fuel concentration distributions in gas jets at high ambient pressures. Except for the spectral dimension, another dimension of the intensified charge coupled device (ICCD) is employed for the spatial resolution of measurements. The effects of laser energy and ambient pressure on plasma dynamics are investigated to explore the feasibility of 1-D LIBS in concentration measurements at high ambient pressure. Since the peak intensity ratio (PIR) of H656/N746 shows significant spatial variations in the plasma volume, a 1-D calibration strategy is developed by establishing respective calibration curves at different spatial positions to quantify the fuel concentration distributions. The measurement uncertainties are evaluated, including both the systematic and random errors. The temporal variations of the 1-D fuel concentration distributions in methane jets are presented, and the shot-to-shot fluctuations are analyzed in detail. The results show that the coefficient of variation of equivalence ratio is lowest at the end of injection (EOI), suggesting that ignition at the EOI could enable a relatively stable flame kernel formation. Along the radial direction of the jet, a high ignitable mixture percentage appears at approximately 3.0 mm from the jet axis at the EOI, suggesting an optimal ignition position. The results reveal that the 1-D LIBS could be a powerful tool for calibration of numerical models and optimal designs of combustion engines taking advantage of high-pressure gas jets.

Experimental study on the gas jet characteristics of a diesel-piloted direct-injection natural gas engine

The natural gas (NG) jet characteristics of NG/diesel dual-fuel injection under different NG injection pressures and dual-fuel injection intervals were studied in a constant volume chamber. The schlieren images showed that the development of NG jet was restricted in both axial and radial directions by diesel spray under dual-fuel injection conditions. Consistently, dual-fuel injection reduced NG jet tip penetration, NG jet cone angle and NG jet volume, yet increased average fuel-air equivalent ratio, compared to NG single-fuel injection. The increase of NG injection pressure from 3 MPa to 5 MPa enhanced NG jet tip penetration and NG jet volume, yet decreased jet cone angle under both single-fuel and dual-fuel injection conditions. The negative effects of diesel spray on NG jet became gradually reduced with the increase of injection interval. When the injection interval was longer than 1.5 ms, NG jet characteristics were close to those under single-fuel conditions.

Computational studies of emission sources in direct fuel injection natural gas engines

The influences of different fuel injection strategies on emission characteristics in a glow plug assisted direct-injection natural gas engine were computationally investigated by a KIVA-3V engine model. A detailed chemical kinetic model and a phenomenological soot model were implemented in the simulation to predict the formation of engine emissions. The simulation reveals that the sac volume of the fuel injector is one of the major contributors to the methane emissions, and the use of a bigger injector nozzle and shorter injection duration can reduce the fuel storage inside the sac volume. In addition, the glow plug shield will trap some fuel mixture and induce relatively rich combustion that contributes a significant amount to both of methane emission and soot particles. Additional openings in the upper part of the glow plug shield may be needed to improve the flow exchange between the shield and the combustion chamber, in order to reduce the emission formation. Further simulation suggests that different fuel injection strategies, such as changing the injection angle and using different injector nozzle sizes associated with different injection durations, could affect the fuel injection, flame propagation and then emission formation inside the glow plug shield and combustion chamber. An optimized fuel injection strategy thereby has potential of reducing the local emission formation inside the glow plug shield and its contribution to the final combustion emissions.

Measurement of cycle-resolved engine-out soot concentration from a diesel-pilot assisted natural gas direct-injection compression-ignition engine

Exhaust-stream particulate matter (PM) emission from combustion sources such as internal combustion engines are typically characterized with modest temporal resolutions; however, in-cylinder investigations have demonstrated significant variability and the importance of individual cycles in transient PM emissions. Here, using a Fast Exhaust Nephelometer (FEN), a methodology is developed for measuring the cycle-specific PM concentration at the exhaust port of a single-cylinder research engine. The measured FEN light-scattering is converted to cycle-resolved soot mass concentration ([Formula: see text]), and used to characterize the variability of engine-out soot emission. To validate this method, exhaust-port FEN measurements are compared with diluted gravimetric PM mass and scanning mobility particle sizer (SMPS) measurements, resulting in close agreements with an overall root-mean-square deviation of better than 30%. It is noted that when PM is sampled downstream in the exhaust system, the particles are larger by 50–70 nm due to coagulation. The response time of the FEN was characterized using a “skip-firing” scheme, by enabling and disabling the fuel injection during otherwise steady-state operation. The average response time due to sample transfer and mixing times is 55 ms, well below the engine cycle period (100 ms) for the considered engine speeds, thus suitable for single-cycle measurements carried out in this work. Utilizing the fast-response capability of the FEN, it is observed that cycle-specific gross indicated mean effective pressure (GIMEP) and [Formula: see text] are negatively correlated ([Formula: see text]: 0.2–0.7), implying that cycles with lower GIMEP emit more soot. The physical causes of this association deserve further investigation, but are expected to be caused by local fuel-air mixing effects. The averaged exhaust-port [Formula: see text] is similar to the diluted gravimetric measurements, but the cycle-to-cycle variations can only be detected with the FEN. The methodology developed here will be used in future investigations to characterize PM emissions during transient engine operation, and to enable exhaust-stream PM measurements for optical engine experiments.