Potential for Reducing Emissions in Reactivity-Controlled Compression Ignition Engines by Fueling Syngas and Diesel

Abstract

A syngas/diesel dual-fuel reactivity-controlled compression ignition (RCCI) engine was numerically investigated by an improved multidimensional model coupled with a reduced chemical mechanism. In the test RCCI engine, the syngas was premixed with air in the intake manifold, while the diesel was directly injected into the cylinder well before top dead center (TDC). The effect of the syngas composition, the premixed ratio of the syngas, the initial in-cylinder temperature at intake valve closing (IVC), and the hydrogen (H2) proportion in the syngas on the RCCI combustion and emission characteristics were investigated. The results indicate that the utilization of the syngas/diesel dual-fuel strategy in the RCCI engine with lean and premixed combustion is capable of simultaneously reducing the emissions of nitrogen oxides (NO x ) and soot. Compared with the gasoline/diesel RCCI combustion, the combustion characteristics of the syngas/diesel RCCI is much more complicated due to the complex composition of syngas, which plays an important role in the ignition and combustion processes. The H2 in the syngas inhibits the autoignition of the RCCI combustion and significantly affects the heat release process, while the inclusion of carbon monoxide (CO) in the syngas is beneficial to mitigate the rapid combustion rate of H2. Consistently, the addition of the inert gases (e.g., N2 and CO2) decreases the global heat release rate and ringing intensity, whereas excessive inert gases in the syngas lead to incomplete combustion and low fuel efficiency. In this study, the optimal solution with the syngas premixed ratio of 60% and the H2 volume fraction of 75% in the syngas can achieve RCCI combustion with both high fuel efficiency and low emissions.

Effects of Syngas Addition on Combustion Characteristics of Gasoline Surrogate Fuel

“…A blended fuel strategy using a mixture of fossil fuel and syngas has been studied by Ji et al, , Singh and Mohapatra, and Krishnamoorthi et al The addition of syngas can also help to improve the combustion efficiency and extend the lean burn limit . Under certain conditions, the efficient and clean combustion can be achieved. , From the above studies, it was found that the application of syngas in dual fuel mode has more potential. Despite all the results obtained, more research and optimizations are still needed to achieve better combustion characteristics.…”

“…8 Under certain conditions, the efficient and clean combustion can be achieved. 15,16 From the above studies, it was found that the application of syngas in dual fuel mode has more potential. Despite all the results obtained, more research and optimizations are still needed to achieve better combustion characteristics.…”

“…Azimov et al 20 constructed a dual fuel mechanism for n -heptane and syngas, and good prediction results were obtained in validation. Ra et al 21 and Xu et al 15 similarly constructed a dual-fuel chemical kinetic model with good prediction results for n -heptane and syngas and analyzed the effects of syngas addition on the reactivity controlled compression ignition (RCCI) engines. Jain et al 17 and Kozlov et al 22 proposed and validated the mechanism of syngas/isooctane hybrid fuels.…”

Detailed Analysis of the Effects of Biodiesel Fraction Increase on the Combustion Stability and Characteristics of a Reactivity-Controlled Compression Ignition Diesel-Biodiesel/Natural Gas Engine

“…Unlike other LTC strategies, such as homogeneous charge compression ignition (HCCI) combustion [14], and partially premixed charge (PPC) combustion [15], RCCI combustion has the advantage of combustion phasing controllability using fuel reactivity stratification [16,17]. Despite the benefits of the RCCI combustion strategy, there are still some challenging problems related to the use of this type of combustion.…”

Large Eddy Simulation of N-Heptane Premixed Flame in Low Temperature Ignition Regime

“…In order to meet the increasingly strict emission regulation, advanced combustion concepts in internal combustion (IC) engines, e.g. Reactivity Controlled Compression Ignition (RCCI), Partially Premixed Combustion (PPC), and Gasoline Compression Ignition (GCI) [2,3], are being developed for higher thermal efficiency and lower emissions. Such advanced IC engines involve high pressure and large hydrocarbon fuels where low temperature combustion (LTC) process plays an important role.…”