Predicting Ignition Delay and Soot Emissions Using Homogenous Reactor CFD Simulations: The Fingerprint of a Fuel Combustion Chemistry Mechanism & Soot Model

Gasoline compression ignition (GCI) engine technology has shown the potential to achieve high fuel efficiency with low criteria pollutant emissions. In order to guide the design and optimization of GCI combustion, it is essential to develop high-fidelity simulation tools. Building on the previous work in computational fluid dynamic (CFD) simulations of spray combustion, this work focuses on predicting the soot emissions in a constant-volume vessel representative of heavy-duty diesel engine applications for an ultra-low sulfur diesel (ULSD) and a high reactivity (Research Octane Number 60) gasoline, and comparing the soot evolution characteristics of the two fuels. Simulations were conducted using both Reynolds Averaged Navier-Stokes (RANS) and Large Eddy Simulation (LES) turbulence models. Extensive model validations were performed against the experimental soot emissions data for both fuels. It was found that the simulation results using the LES turbulence model agreed better with the measured ignition delays and liftoff lengths than the RANS turbulence model. In addition, two soot models were evaluated in the current study, including an empirical two-step soot formation and oxidation model, and a detailed soot model that involves poly-aromatic hydrocarbon (PAH) chemistry. Validations showed that the separation of the flame lift-off location and the soot lift-off location and the relative natural luminosity signals were better predicted by the detailed soot model combined with the LES turbulence model. Qualitative comparisons of simulated local soot concentration distributions against experimental measurements in the literature confirmed the model’s performance. CFD simulations showed that the transition of domination from soot formation to soot oxidation was fuel-dependent, and the two fuels exhibited different temporal and spatial characteristics of soot emissions. CFD simulations also confirmed the lower sooting propensity of gasoline compared to ULSD under all investigated conditions.

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Mapping the combustion modes of a dual-fuel compression ignition engine

International Journal of Engine Research ◽

10.1177/14680874211018376 ◽

2021 ◽

pp. 146808742110183

Author(s):

Jonathan Martin ◽

André Boehman

Keyword(s):

Direct Injection ◽

Fuel Combustion ◽

Dual Fuel ◽

Compression Ignition ◽

Compression Ignition Engine ◽

Combustion Modes ◽

Si Engines ◽

Dual Fuel Combustion ◽

Soot Emissions ◽

Ci Engines

Compression-ignition (CI) engines can produce higher thermal efficiency (TE) and thus lower carbon dioxide (CO2) emissions than spark-ignition (SI) engines. Unfortunately, the overall fuel economy of CI engine vehicles is limited by their emissions of nitrogen oxides (NOx) and soot, which must be mitigated with costly, resource- and energy-intensive aftertreatment. NOx and soot could also be mitigated by adding premixed gasoline to complement the conventional, non-premixed direct injection (DI) of diesel fuel in CI engines. Several such “dual-fuel” combustion modes have been introduced in recent years, but these modes are usually studied individually at discrete conditions. This paper introduces a mapping system for dual-fuel CI modes that links together several previously studied modes across a continuous two-dimensional diagram. This system includes the conventional diesel combustion (CDC) and conventional dual-fuel (CDF) modes; the well-explored advanced combustion modes of HCCI, RCCI, PCCI, and PPCI; and a previously discovered but relatively unexplored combustion mode that is herein titled “Piston-split Dual-Fuel Combustion” or PDFC. Tests show that dual-fuel CI engines can simultaneously increase TE and lower NOx and/or soot emissions at high loads through the use of Partial HCCI (PHCCI). At low loads, PHCCI is not possible, but either PDFC or RCCI can be used to further improve NOx and/or soot emissions, albeit at slightly lower TE. These results lead to a “partial dual-fuel” multi-mode strategy of PHCCI at high loads and CDC at low loads, linked together by PDFC. Drive cycle simulations show that this strategy, when tuned to balance NOx and soot reductions, can reduce engine-out CO2 emissions by about 1% while reducing NOx and soot by about 20% each with respect to CDC. This increases emissions of unburnt hydrocarbons (UHC), still in a treatable range (2.0 g/kWh) but five times as high as CDC, requiring changes in aftertreatment strategy.

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A physics-based approach to modeling real-fuel combustion chemistry – VII. Relationship between speciation measurement and reaction model accuracy

Combustion and Flame ◽

10.1016/j.combustflame.2020.10.023 ◽

2020 ◽

Author(s):

Rui Xu ◽

Hai Wang

Keyword(s):

Reaction Model ◽

Fuel Combustion ◽

Model Accuracy ◽

Combustion Chemistry

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Semi-physical NOx and soot model for CI engines: Study of its calibration procedure and portability

Proceedings of the Institution of Mechanical Engineers Part D Journal of Automobile Engineering ◽

10.1177/0954407020931686 ◽

2020 ◽

Vol 234 (14) ◽

pp. 3414-3428

Author(s):

Hassan Karaky ◽

Pierre Marty ◽

Xavier Tauzia ◽

Alain Maiboom ◽

Gilles Mauviot

Keyword(s):

Sensitivity Analysis ◽

Physical Model ◽

Diesel Engines ◽

Calibration Procedure ◽

Original Analysis ◽

Soot Emissions ◽

Ci Engines ◽

Soot Model

A series of papers has previously presented a semi-physical model for NOx and soot emissions prediction for diesel engines. In this paper, the work is continued with an original analysis of the model’s capacity to be ported to a new engine and a sensitivity analysis of the number of training points required to obtain the desired accuracy. These two aspects are rarely developed in similar studies.

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Investigation of the impact of injection timing and pressure on emissions characteristics and smoke/soot emissions in diesel engine fuelling with soybean fuel

Journal of Engineering Research ◽

10.36909/jer.v9i2.9683 ◽

2021 ◽

Vol 9 (2) ◽

Author(s):

Mohammed A. Fayad ◽

Keyword(s):

Diesel Engine ◽

Diesel Fuel ◽

Fuel Combustion ◽

Pollutant Emissions ◽

Injection Timing ◽

Injection Strategy ◽

Renewable Fuel ◽

Soybean Biodiesel ◽

Soot Emissions ◽

The Impact

Engine injection strategy and renewable fuel both can improve nitrogen oxides (NOX) and smoke/soot emissions in a common-rail compression ignition (CI) diesel engine. The effects of different postinjection (PI) timings (15, 30, and 45) after top dead center (aTDC) and injection pressures (550 and 650 bar) on pollutant emissions and smoke/soot emissions were investigated for combustion of a renewable fuel (soybean biodiesel). The results showed that the levels of carbon monoxide (CO), hydrocarbons (HCs), and NOX are reduced from the combustion of soybean biodiesel compared to the diesel fuel combustion for different injection strategy. Besides, NOX emission is clearly reduced with retarded PI timing, especially at 45°. It is found that the increasing injection pressure reduced gaseous emissions for both fuels. The combination between biodiesel fuel and injection strategy can provide meaningful improvements in pollutant emissions, as well as enhance the exhaust temperature compared to the diesel fuel. With biodiesel fueling, smoke/soot emissions were reduced from biodiesel combustion (by 19.7%) under different fuel injection timings and pressures rather than from the diesel fuel combustion (by 12.2%).

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