scholarly journals Dependence of premixed low-temperature diesel combustion on fuel ignitability and volatility

2011 ◽  
Vol 13 (1) ◽  
pp. 14-27 ◽  
Author(s):  
T Li ◽  
R Moriwaki ◽  
H Ogawa ◽  
R Kakizaki ◽  
M Murase
Keyword(s):  
Low Temperature ◽  
Oxygen Concentration ◽  
Ignition Delay ◽  
Internal Combustion Engines ◽  
Cetane Number ◽  
Coefficient Of Determination ◽  
Injection Timing ◽  
Low Temperature Combustion ◽  
Load Range ◽  
Wide Range

A comprehensive study of fuel property effects in internal combustion engines is required to enable fuel diversification as well as the development of applications to advanced engines for operation with a variety of combustion modes. The objective of this paper is to investigate the effects of fuel ignitability and volatility over a wide range of premixed low-temperature combustion (LTC) modes in diesel engines. A total of 23 fuels were prepared from commercial gasoline, kerosene, and diesel as baseline fuels and with the addition of additives, to generate a cetane number (CN) range from 11 to 75. Experiments with a single-cylinder diesel engine operated in moderately advanced-injection LTC modes were conducted to evaluate these fuels. The combustion phasing is demonstrated to be a good indicator to estimate the in-cylinder peak pressure, exhaust gas emissions, and thermal efficiency in the LTC mode. Fuel ignitability affects the combustion phasing by changing the ignition delay. The predicted cetane number (PCN) based on fuel molecular structure analysis can be fitted to the ignition delays with a higher coefficient of determination than CN, suggesting good potential as a fuel ignitability measure over a wide range. The stable operating load range in the smokeless LTC mode depends more on the actual ignition delay or PCN rather than CN. With fixed injection timing and intake oxygen concentration, O2in, only when PCN < 40, the load range can be expanded significantly to higher loads. By holding the combustion phasing at top dead centre and varying intake oxygen concentration, the nitrogen oxides and smoke emissions become limitations of the load expansion for some fuels. The effects of fuel volatility on the characteristics of LTC are small compared to ignitability. Finally, the operational injection timing range and robustness of the LTC to fuel ignitability are examined, showing that the advantageous ignitability range becomes narrower, with fuel ignitability decreasing.

Enhancing Low-Temperature Combustion With Biodiesel Blending in a Diesel Engine at a Medium Load Condition

2015 ◽  
Vol 138 (4) ◽  
Author(s):  
Sunyoup Lee ◽  
Seungmook Oh ◽  
Junghwan Kim ◽  
Duksang Kim
Keyword(s):  
Diesel Engine ◽  
Low Temperature ◽  
Oxygen Concentration ◽  
Load Condition ◽  
Low Temperature Combustion ◽  
Effective Pressure ◽  
Oxygen Level ◽  
Indicated Mean Effective Pressure ◽  
Wide Range ◽  
Temperature Combustion

The present study investigated the effects of biodiesel blending under a wide range of intake oxygen concentration levels in a diesel engine. This study attempted to identify the lowest biodiesel blending rate that achieves acceptable levels of nitric oxides (NOx), soot, and coefficient of variation in the indicated mean effective pressure (COVIMEP). Biodiesel blending was to be minimized in order to reduce the fuel penalty associated with the biodiesels lower caloric value (LCV). Engine experiments were performed in a 1 l single-cylinder diesel engine at an engine speed of 1400 rev/min under a medium load condition. The blend rate and intake oxygen concentration were varied independently of each other at a constant intake pressure of 200 kPa. The biodiesel blend rate varied from 0% (B000) to 100% biodiesel (B100) at a 20% increment. The intake oxygen level was adjusted from 8% to 19% by volume (vol. %) in order to embrace both conventional and low-temperature combustion (LTC) operations. A fixed injection duration of 788 ms at a fuel rail pressure of 160 MPa exhibited a gross indicated mean effective pressure (IMEP) between 750 kPa and 910 kPa, depending on the intake oxygen concentration. The experimental results indicated that the intake oxygen level had to be below 10 vol. % to achieve the indicated specific NOx (ISNOx) below 0.2 g/kW h with the B000 fuel. However, a substantial soot increase was exhibited at such a low intake oxygen level. Biodiesel blending reduced NOx until the blending rate reached 60% with reduced in-cylinder temperature due to lower total energy release. As a result, 60% biodiesel-blended diesel (B060) achieved NOx, soot, and COVIMEP of 0.2 g/kW h, 0.37 filter smoke number (FSN), and 0.5, respectively, at an intake oxygen concentration of 14 vol. %. The corresponding indicated thermal efficiency was 43.2%.

Enhancing Low Temperature Combustion With Biodiesel Blending in a Diesel Engine at a Medium Load Condition

2014 ◽  
Author(s):  
Sunyoup Lee ◽  
Seungmook Oh ◽  
Junghwan Kim ◽  
Duksang Kim
Keyword(s):  
Diesel Engine ◽  
Low Temperature ◽  
Oxygen Concentration ◽  
Load Condition ◽  
Low Temperature Combustion ◽  
Effective Pressure ◽  
Oxygen Level ◽  
Indicated Mean Effective Pressure ◽  
Wide Range ◽  
Temperature Combustion

The present study investigated the effects of biodiesel blending under a wide range of intake oxygen concentration levels in a diesel engine. This study attempted to identify the lowest biodiesel blending rate that achieves acceptable levels of nitric oxides (NOx), soot, and coefficient of variation in the indicated mean effective pressure (COVIMEP). Biodiesel blending was to be minimized in order to reduce the fuel penalty associated with the biodiesels lower caloric value. Engine experiments were performed in a 1-liter single-cylinder diesel engine at an engine speed of 1400 rev/min under a medium load condition. The blend rate and intake oxygen concentration were varied independently of each other at a constant intake pressure of 200 kPa. The biodiesel blend rate varied from 0% (B000) to 100% biodiesel (B100) at a 20% increment. The intake oxygen level was adjusted from 8 to 19% by volume (vol %) in order to embrace both conventional and low-temperature combustion (LTC) operations. A fixed injection duration of 788 μs at a fuel rail pressure of 160 MPa exhibited a gross indicated mean effective pressure (IMEP) between 750 kPa and 910 kPa, depending on the intake oxygen concentration. The experimental results indicated that the intake oxygen level had to be below 10 vol% to achieve the indicated specific NOx (ISNOx) below 0.2g/kWhr with the B000 fuel. However, a substantial soot increase was exhibited at such a low intake oxygen level. Biodiesel blending reduced NOx until the blending rate reached 60% with reduced in-cylinder temperature due to lower total energy release. As a result, 60%-biodiesel blended diesel (B060) achieved NOx, soot, and COVIMEP of 0.2 g/kWhr, 0.37 filter smoke number (FSN), and 0.5, respectively, at an intake oxygen concentration of 14 vol%. The corresponding indicated thermal efficiency was 43.2%.

Low Cetane Fuels in Compression Ignition Engine to Achieve LTC

2011 ◽  
Author(s):  
Swami Nathan Subramanian ◽  
Stephen Ciatti
Keyword(s):  
Low Temperature ◽  
Internal Combustion Engines ◽  
High Efficiency ◽  
Fuel Efficiency ◽  
Nox Emissions ◽  
Low Temperature Combustion ◽  
Compression Ignition ◽  
Oxides Of Nitrogen ◽  
Compression Ignition Engine ◽  
Conventional Combustion

The conventional combustion processes of Spark Ignition (SI) and Compression Ignition (CI) have their respective merits and demerits. Internal combustion engines use certain fuels to utilize those conventional combustion technologies. High octane fuels are required to operate the engine in SI mode, while high cetane fuels are preferable for CI mode of operation. Those conventional combustion techniques struggle to meet the current emissions norms while retaining high efficiency. In particular, oxides of nitrogen (NOx) and particulate matter (PM) emissions have limited the utilization of diesel fuel in compression ignition engines, and conventional gasoline operated SI engines are not fuel efficient. Advanced combustion concepts have shown the potential to combine fuel efficiency and improved emissions performance. Low Temperature Combustion (LTC) offers reduced NOx and PM emissions with comparable modern diesel engine efficiencies. The ability of premixed, low-temperature compression ignition to deliver low PM and NOx emissions is dependent on achieving optimal combustion phasing. Variations in injection pressures, injection schemes and Exhaust Gas Recirculation (EGR) are studied with low octane gasoline LTC. Reductions in emissions are a function of combustion phasing and local equivalence ratio. Engine speed, load, EGR quantity, compression ratio and fuel octane number are all factors that influence combustion phasing. Low cetane fuels have shown comparable diesel efficiencies with low NOx emissions at reasonably high power densities.

Fuel-Sensitive Ignition Delay Models for a Local and Global Description of Direct Injection Internal Combustion Engines

2015 ◽  
Vol 137 (11) ◽  
Author(s):  
Kyoung Hyun Kwak ◽  
Claus Borgnakke ◽  
Dohoy Jung
Keyword(s):  
Ignition Delay ◽  
Alternative Fuels ◽  
Internal Combustion Engines ◽  
Cetane Number ◽  
Global Model ◽  
Local Model ◽  
Delay Model ◽  
Lower Accuracy ◽  
Delay Models ◽  
Single Calibration

Models for ignition delay are investigated and fuel-specific properties are included to predict the effects of different fuels on the ignition delay. These models follow the Arrhenius type expression for the ignition delay modified with the oxygen concentration and Cetane number to extend the range of validity. In this investigation, two fuel-sensitive spray ignition delay models are developed: a global model and a local model. The global model is based on the global combustion chamber charge properties including temperature, pressure, and oxygen/fuel content. The local model is developed to account for temporal and spatial variations in properties of separated spray zones such as local temperature, oxidizer, and fuel concentrations obtained by a quasi-dimensional multizone fuel spray model. These variations are integrated in time to predict the ignition delay. Often ignition delay models are recalibrated for a specific fuel but in this study, the global ignition delay model includes the Cetane number to capture ignition delay of various fuels. The local model uses Cetane number and local stoichiometric oxygen to fuel molar ratio. The model is therefore capable of predicting spray ignition delays for a set of fuels with a single calibration. Experimental dataset of spray ignition delay in a constant volume chamber is used for model development and calibration. The models show a good accuracy for the predicted ignition delay of four different fuels: JP8, DF2, n-heptane, and n-dodecane. The investigation revealed that the most accurate form of the models is from a calibration done for each individual fuel with only a slight decrease in accuracy when a single calibration is done for all fuels. The single calibration case is the more desirable outcome as it leads to general models that cover all the fuels. Of the two proposed models, the local model has a slightly better accuracy compared to the global model. Results for both models demonstrate the improvements that can be obtained for the ignition delay model when additional fuel-specific properties are included in the spray ignition model. Other alternative fuels like synthetic oxygenated fuels were included in the investigation. These fuels behave differently such that the Cetane number does not provide the same explanation for the trend in ignition delay. Though of lower accuracy, the new models do improve the predictive capability when compared with existing types of ignition delay models applied to this kind of fuels.

Investigation of the Roles of Flame Propagation, Turbulent Mixing, and Volumetric Heat Release in Conventional and Low Temperature Diesel Combustion

2011 ◽  
Vol 133 (10) ◽  
Author(s):  
Sage L. Kokjohn ◽  
Rolf D. Reitz
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Oxygen Concentration ◽  
Reaction Zone ◽  
Flame Propagation ◽  
Ignition Delay ◽  
Flame Structure ◽  
Combustion Model ◽  
Combustion Mode ◽  
Flame Structures

In this work, a multimode combustion model that combines a comprehensive kinetics scheme for volumetric heat release and a level-set-based model for turbulent flame propagation is applied over the range of engine combustion regimes from non-premixed to premixed conditions. The model predictions of the ignition processes and flame structures are compared with the measurements from the literature of naturally occurring luminous emission and OH planar laser induced fluorescence. Comparisons are performed over a range of conditions from a conventional diesel operation (i.e., short ignition delay, high oxygen concentration) to a low temperature combustion mode (i.e., long ignition delay, low oxygen concentration). The multimode combustion model shows an excellent prediction of the bulk thermodynamic properties (e.g., rate of heat release), as well as local phenomena (i.e., ignition location, fuel and combustion intermediate species distributions, and flame structure). The results of this study show that, even in the limit of mixing controlled combustion, the flame structure is captured extremely well without considering subgrid scale turbulence-chemistry interactions. The combustion process is dominated by volumetric heat release in a thin zone around the periphery of the jet. The rate of combustion is controlled by the transport of a reactive mixture to the reaction zone, and the dominant mixing processes are well described by the large scale mixing and diffusion. As the ignition delay is increased past the end of injection (i.e., positive ignition dwell), both the simulations and optical engine experiments show that the reaction zone spans the entire jet cross section. In this combustion mode, the combustion rate is no longer limited by the transport to the reaction zone, but rather by the kinetic time scales. Although comparisons of results with and without consideration of flame propagation show very similar flame structures and combustion characteristics, the addition of the flame propagation model reveals details of the edge or triple-flame structure in the region surrounding the diffusion flame at the lift-off location. These details are not captured by the purely kinetics based combustion model, but are well represented by the present multimode model.

Investigation of the Roles of Flame Propagation, Turbulent Mixing, and Volumetric Heat Release in Conventional and Low Temperature Diesel Combustion

2010 ◽  
Author(s):  
Sage L. Kokjohn ◽  
Rolf D. Reitz
Keyword(s):  
Low Temperature ◽  
Heat Release ◽  
Oxygen Concentration ◽  
Reaction Zone ◽  
Flame Propagation ◽  
Ignition Delay ◽  
Flame Structure ◽  
Combustion Model ◽  
Combustion Mode ◽  
Multi Mode

In this work, a multi-mode combustion model, that combines a comprehensive kinetics scheme for volumetric heat release and a level-set-based model for turbulent flame propagation, is applied over the range of engine combustion regimes from non-premixed to premixed conditions. Model predictions of the ignition processes and flame structures are compared to measurements from the literature of naturally occurring luminous emission and OH planar laser induced fluorescence (PLIF). Comparisons are performed over a range of conditions from conventional diesel operation (i.e., short ignition delay, high oxygen concentration) to a low temperature combustion mode (i.e., long ignition delay, low oxygen concentration). The multi-mode combustion model shows excellent prediction of the bulk thermodynamic properties (e.g., rate of heat release), as well as local phenomena (i.e., ignition location, fuel and combustion intermediate species distributions, and flame structure). The results of this study show that even in the limit of mixing controlled combustion, the flame structure is captured extremely well without considering sub-grid scale turbulence-chemistry interactions. The combustion process is dominated by volumetric heat release in a thin zone around the periphery of the jet. The rate of combustion is controlled by transport of reactive mixture to the reaction zone and the dominant mixing processes are well described by the large scale mixing and diffusion. As the ignition delay is increased past the end of injection (i.e., positive ignition dwell), both the simulations and optical diagnostics show that the reaction zone spans the entire jet cross-section. In this combustion mode the combustion rate is no longer limited by transport to the reaction zone, but rather by kinetic timescales. Although comparisons of results with and without consideration of flame propagation show very similar flame structures and combustion characteristics, the addition of the flame propagation model reveals details of the edge or triple-flame structure in the region surrounding the diffusion flame at the lift off location. These details are not captured by the purely kinetics based combustion model, but are well represented by the present multi-mode model.

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