scholarly journals Effects of injection parameters, boost, and swirl ratio on gasoline compression ignition operation at idle and low-load conditions

2016 ◽  
Vol 18 (8) ◽  
pp. 824-836 ◽  
Author(s):  
Janardhan Kodavasal ◽  
Christopher P Kolodziej ◽  
Stephen A Ciatti ◽  
Sibendu Som
Keyword(s):  
Load Condition ◽  
Injection Pressure ◽  
Operating Conditions ◽  
Compression Ignition ◽  
Swirl Ratio ◽  
Injector Nozzle ◽  
Low Load ◽  
Dynamics Simulations ◽  
Compression Ignition Combustion ◽  
Injection Pressures

In this work, we study the effects of injector nozzle inclusion angle, injection pressure, boost, and swirl ratio on gasoline compression ignition combustion. Closed-cycle computational fluid dynamics simulations using a 1/7th sector mesh representing a single cylinder of a four-cylinder 1.9 L diesel engine, operated in gasoline compression ignition mode with 87 anti-knock index (AKI) gasoline, were performed. Two different operating conditions were studied—the first is representative of idle operation (4 mg fuel/cylinder/cycle, 850 r/min), and the second is representative of a low-load condition (10 mg fuel/cylinder/cycle, 1500 r/min). The mixture preparation and reaction space from the simulations were analyzed to gain insights into the effects of injection pressure, nozzle inclusion angle, boost, and swirl ratio on achieving stable low-load to idle gasoline compression ignition operation. It was found that narrower nozzle inclusion angles allow for more reactivity or propensity to ignition (determined qualitatively by computing constant volume ignition delays) and are suitable over a wider range of injection timings. Under idle conditions, it was found that lower injection pressures helped to reduce overmixing of the fuel, resulting in greater reactivity and ignitability (ease with which ignition can be achieved) of the gasoline. However, under the low-load condition, lower injection pressures did not increase ignitability, and it is hypothesized that this is because of reduced chemical residence time resulting from longer injection durations. Reduced swirl was found to maintain higher in-cylinder temperatures through compression, resulting in better ignitability. It was found that boosting the charge also helped to increase reactivity and advanced ignition timing.

Effects of Injector Nozzle Inclusion Angle on Extending the Lower Load Limit of Gasoline Compression Ignition Using 87 AKI Gasoline

2014 ◽  
Author(s):  
Christopher P. Kolodziej ◽  
Stephen A. Ciatti
Keyword(s):  
Injection Pressure ◽  
Premixed Combustion ◽  
Injection Timing ◽  
Compression Ignition ◽  
Effective Pressure ◽  
Advantages And Disadvantages ◽  
Injector Nozzle ◽  
Brake Mean Effective Pressure ◽  
Low Load ◽  
Ignition Propensity

Gasoline Compression Ignition (GCI) is a promising single-fuel advanced combustion concept for increased efficiency and reduced emissions in comparison with current conventional combustion modes. Gasoline fuels are advantageous in premixed combustion concepts because of their increased volatility and reduced reactivity compared to diesel. These qualities help reduce emissions of particulate matter (PM) and oxides of nitrogen (NOx), while making combustion phasing (and therefore combustion noise reduction) easier to manage. One of the challenges of using a gasoline with an anti-knock index (AKI) of 87 in a premixed combustion concept is being able to achieve stable low load operation. (Note that AKI is equivalent to (RON + MON)/2.) With such small injection quantities of a relatively more volatile and less reactive fuel than diesel, the injection timing of minimum load fueling needs to be early enough to allow the auto-ignition chemistry enough time, but late enough to keep the fuel from over-mixing and losing ignition propensity. The objective of this study was to investigate the advantages and disadvantages of reducing the injector nozzles’ inclusion angle from 148° to 120° on the combustion and emissions performance of GCI at 850 RPM and low load. To assess these effects, minimum fueling injection timing sweeps were performed with a 3% coefficient of variance of indicated mean effective pressure with each injector nozzle angle at 500 and 250 bar injection pressure. The results from these experiments revealed that both reduced injector nozzle angle and reduced injection pressure increased ignition propensity and allowed for reduced fueling and stable low load extension to 1 bar brake mean effective pressure using 87 AKI gasoline without any external boosting or heating. Combustion characteristics (such as noise) and emissions are discussed.

scholarly journals A thermodynamic model for homogeneous charge compression ignition combustion with recompression valve events and direct injection: Part I — Adiabatic core ignition model

2016 ◽  
Vol 18 (7) ◽  
pp. 657-676 ◽  
Author(s):  
Prasad S Shingne ◽  
Robert J Middleton ◽  
Dennis N Assanis ◽  
Claus Borgnakke ◽  
Jason B Martz
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Homogeneous Charge Compression Ignition ◽  
Direct Injection ◽  
Operating Conditions ◽  
Compression Ignition ◽  
Auto Ignition ◽  
Dynamics Simulations ◽  
Compression Ignition Combustion ◽  
Homogeneous Charge

This two-part article presents a model for boosted and moderately stratified homogeneous charge compression ignition combustion for use in thermodynamic engine cycle simulations. The model consists of two components: one an ignition model for the prediction of auto-ignition onset and the other an empirical combustion rate model. This article focuses on the development and validation of the homogeneous charge compression ignition model for use under a broad range of operating conditions. Using computational fluid dynamics simulations of the negative valve overlap valve events typical of homogeneous charge compression ignition operation, it is shown that there is no noticeable reaction progress from low-temperature heat release, and that ignition is within the high-temperature regime ( T > 1000 K), starting within the highest temperature cells of the computational fluid dynamics domain. Additional parametric sweeps from the computational fluid dynamics simulations, including sweeps of speed, load, intake manifold pressures and temperature, dilution level and valve and direct injection timings, showed that the assumption of a homogeneous charge (equivalence ratio and residuals) is appropriate for ignition modelling under the conditions studied, considering the strong sensitivity of ignition timing to temperature and its weak compositional dependence. Use of the adiabatic core temperature predicted from the adiabatic core model resulted in temperatures within ±1% of the peak temperatures of the computational fluid dynamics domain near the time of ignition. Thus, the adiabatic core temperature can be used within an auto-ignition integral as a simple and effective method for estimating the onset of homogeneous charge compression ignition auto-ignition. The ignition model is then validated with an experimental 92.6 anti-knock index gasoline-fuelled homogeneous charge compression ignition dataset consisting of 290 data points covering a wide range of operating conditions. The tuned ignition model predictions of [Formula: see text] have a root mean square error of 1.7° crank angle and R2 = 0.63 compared to the experiments.

Parametric Study to Optimize Gasoline Compression Ignition Operation under Low Load Condition Using CFD

2021 ◽  
Author(s):  
Jihad Badra ◽  
Alma Alhussaini ◽  
Jaeheon Sim ◽  
Yoann Viollet ◽  
Amer Amer
Keyword(s):  
Parametric Study ◽  
Load Condition ◽  
Compression Ignition ◽  
Low Load

Performance of Francis Turbine Operating at Excess Load Condition

2020 ◽  
Author(s):  
Muhannad Altimemy ◽  
Justin Caspar ◽  
Alparslan Oztekin
Keyword(s):  
Flow Field ◽  
Draft Tube ◽  
Turbine Blades ◽  
Pressure Fluctuations ◽  
Load Condition ◽  
Operating Conditions ◽  
Francis Turbine ◽  
Partial Load ◽  
Dynamics Simulations ◽  
Excess Load

Abstract Computational fluid dynamics simulations are conducted to characterize the spatial and temporal characteristics of the flow field inside a Francis turbine operating in the excess load regime. A high-fidelity Large Eddy Simulation (LES) turbulence model is applied to investigate the flow-induced pressure fluctuations in the draft tube of a Francis Turbine. Probes placed alongside the wall and in the center of the draft tube measure the pressure signal in the draft tube, the pressure over the turbine blades, and the power generated to compare against previous studies featuring design point and partial load operating conditions. The excess load is seen during Francis turbines in order to satisfy a spike in the electrical demand. By characterizing the flow field during these conditions, we can find potential problems with running the turbine at excess load and inspire future studies regarding mitigation methods. Our studies found a robust low-pressure region on the edges of turbine blades, which could cause cavitation in the runner region, which would extend through the draft tube, and high magnitude of pressure fluctuations were observed in the center of the draft tube.

Molecular Dynamics Simulation on the Friction Properties of Couette Flow With Superhydrophobic Rough Surfaces Under Different Load

2019 ◽  
Author(s):  
Chengzhi Hu ◽  
Dawei Tang ◽  
Jizu Lv ◽  
Minli Bai ◽  
Xiaoliang Zhang
Keyword(s):  
Molecular Dynamics ◽  
Couette Flow ◽  
Load Condition ◽  
Friction Reduction ◽  
Dynamics Simulation ◽  
Flow Properties ◽  
Opposite Trend ◽  
Low Load ◽  
High Load Condition ◽  
Dynamics Simulations

Abstract To reveal the effect of superhydrophobic rough surface on the friction properties, molecular dynamics simulations are used to study the friction properties of Couette flow. In particular, the influence of load on the flow properties is considered in this work. Results show that there is a critical load (Pcrit), and the friction-reduction properties of superhydrophobic surfaces with stripes are only presented when the load is smaller than the Pcrit. With the decrease in the distance between stripes, the Pcrit is increased. Under a low load, the friction force is increased with increasing the distance between stripes. However, under high load condition we observe an opposite trend. The height of stripe has little impacts on the Pcrit.

Parametric Study of Ignition and Combustion Characteristics From a Gasoline Compression Ignition Engine Using Two Different Reactivity Fuels

2016 ◽  
Author(s):  
Khanh Cung ◽  
Toby Rockstroh ◽  
Stephen Ciatti ◽  
William Cannella ◽  
S. Scott Goldsborough
Keyword(s):  
High Speed ◽  
Injection Pressure ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Injection Timing ◽  
Strong Impact ◽  
Boost Pressure ◽  
Compression Ignition ◽  
Compression Ignition Engine ◽  
Ignition And Combustion

Unlike homogeneous charge compression ignition (HCCI) that has the complexity in controlling the start of combustion event, partially premixed combustion (PPC) provides the flexibility of defining the ignition timing and combustion phasing with respect to the time of injection. In PPC, the stratification of the charge can be influenced by a variety of methods such as number of injections (single or multiple injections), injection pressure, injection timing (early to near TDC injection), intake boost pressure, or combination of several factors. The current study investigates the effect of these factors when testing two gasoline-like fuels of different reactivity (defined by Research Octane Number or RON) in a 1.9-L inline 4-cylinder diesel engine. From the collection of engine data, a full factorial analysis was created in order to identify the factors that most influence the outcomes such as the location of ignition, combustion phasing, combustion stability, and emissions. Furthermore, the interaction effect of combinations of two factors or more was discussed with the implication of fuel reactivity under current operating conditions. The analysis was done at both low (1000 RPM) and high speed (2000 RPM). It was found that the boost pressure and air/fuel ratio have strong impact on ignition and combustion phasing. Finally, injection-timing sweeps were conducted whereby the ignition (CA10) of the two fuels with significantly different reactivity were matched by controlling the boost pressure while maintaining a constant lambda (air/fuel equivalence ratio).

Experimental Investigations of Cycle-to-Cycle and Cylinder-to-Cylinder Variation of PCCI Combustion With High Injection Pressures

2010 ◽  
Author(s):  
S. Juttu ◽  
S. S. Thipse ◽  
Praveen Mishra ◽  
N. B. Dhande ◽  
N. V. Marathe ◽  
...  
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Injection Pressure ◽  
Combustion Mode ◽  
Operating Range ◽  
High Injection ◽  
Wide Range ◽  
Significant Difference ◽  
Low Load ◽  
Injection Pressures

Recently HCCI combustion concept has gained the attention of industry and academia due to its potential to reduce NOx and PM emissions simultaneously from diesel engines. The HCCI concept also called as Partially-Premixed Charge Compression Ignition (PCCI) when heavy fuel like diesel is used as fuel. To achieve homogeneous mixture of diesel+air+residual gases, high injection pressures are required with fine atomization. The cycle-to-cycle and cylinder-to-cylinder variations in rail pressure and EGR ratio caused to variations in engine performance. In this study combustion stabilities and cycle-to-cycle variations of diesel engine operated in PCCI combustion mode were investigated at different fuel injection pressures on a 4-cylinder, 4-stroke diesel engine. The experiments were conducted with 500bar, 1000bar, 1500bar and 1800bar injection pressures at low load (IMEP = 2bar) and 50% load (IMEP = 8.5bar) at 2500 and 3000 rpm. No EGR was used at low load condition and 50% EGR was used at 50% load at all injection pressures. In-cylinder pressures of 100 cycles were recorded for each test conditions running with PCCI mode. Consequently, cycle-to-cycle variations of the maximum Rate of Heat Release (ROHRmax), maximum Total Heat Release (THRmax), IMEP and Pmax were analyzed and evaluated using Coefficient of Variation (COV) of each parameter. The significant difference in COV from cylinder-to-cylinder was observed at higher injection pressures. With high injection pressures, wide range of cycle-to-cycle variations were observed in engines operated in PCCI combustion mode limiting the injection pressure and operating range of engine. The results show that the injection pressure need to be optimized with respect to load to control the PCCI combustion at constant EGR ratio to minimize the cycle-to-cycle variations and also extend the operating range of PCCI mode.

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