Low Reactivity Fuels Research Articles

An experimental evaluation of engine performance and emissions characteristics of a modified direct injection diesel engine operated in RCCI mode

This study explored methods to evaluate the test engine characteristics operated based on the reactivity controlled compression ignition (RCCI) technology to reduce fuel consumption and exhaust emissions, especially PM and NOx. Consequently, gasoline and diesel, respectively, considered as the low reactivity fuel (LRF) and high reactivity fuel (HRF), are injected in the intake manifold and combustion chamber. The experimental procedure is conducted at a constant speed of 2000 rpm, and brake mean effective pressure (BMEP) from low load 0.84 bar to high load 4.24 bar. The injection strategy is varied according to the engine loads. Indeed, at the low and medium engine load condition, the diesel fuel is injected double injection pulse, at the high load, the diesel fuel is injected single injection pulse. The injection timing is advanced from the top dead center (TDC) until knocking happens or the coefficient of variation (COV) higher than 10%, and maximum advanced injection timing is 65 crank angle degree (℃A) before the top dead center (BTDC). The results of advanced injection timing show that limit of advanced timing in low load is COV while at high load is knocking; at medium load, the diesel injection timing can be advanced to 65℃A BTDC. The exhaust emissions of CO and HC are higher than conventional diesel engines, while soot is hugely lower in all operating points. NOx emission is much dependent on injection timing, at 10 to 20℃A BTDC NOx highest, and approximately to the conventional diesel engine, NOx reduction when injection timing advanced.

Efficient light-duty engine using turbulent jet ignition of lean methane mixtures

Diesel engines use diffusion-controlled combustion of a high-reactivity fuel and offer high efficiencies because they combine lean combustion with a high compression ratio. For low-reactivity fuels such as gasoline or natural gas, premixed combustion is used, which leads to lower efficiency levels as usually stoichiometric combustion is combined with lower compression ratios. Trying to apply diesel-like process parameters to low-reactivity fuels inevitably leads to problems with classical spark ignition systems as they are not able to establish robust flame propagation for such hard-to-ignite conditions. One possibility to enable fast combustion for diluted mixtures at high pressure levels is to establish ignition in a prechamber and ignite the charge of the main combustion chamber using the turbulent jets exiting the prechamber. In this study, the experimental results of a prechamber-equipped four-cylinder natural gas engine with 2 L displacement are discussed in detail. In the majority of the engine map, auxiliary fueling is used in the prechamber and a global air–fuel equivalence ratio λ is set to 1.7. At full load, a λ of 1.5 is applied without auxiliary prechamber fueling. The experiments show that such a setup is able to achieve brake efficiency levels of above 45% while maintaining peak brake mean effective pressure levels above 20 bar. At high load conditions, cylinder pressure levels at ignition timing achieve more than 80 bar and cylinder peak pressures of around 180 bars occur. The technology proved to enable robust and very fast combustion at comparably low NOxlevels. A remaining challenge for the on-road use of such a technology is the reduction of the methane emissions at lean conditions.

Development of integral type spent fuel pool storage rack with gadolinium and europium-containing structure materials

This study presents the development of a new integral-type rack design, characterized by the use of gadolinium (Gd)-containing structure materials that enhances the capacity of spent fuel (SF) pool storage by exploiting the high neutron absorption capability of Gd. Appropriate types and contents of Gd-based neutron-absorbing materials are selected for the new design through parametric studies. For high-reactivity fuels (region I of SF storage pools), neutron-absorbing material composed of Gd 0.7 at% with Eu 2.73 at% is found to be an optimal neutron absorber whereas for low-reactivity fuels (region II of SF storage pools), a composition of Gd 0.7 at% with Eu 8.38 at% is found to be optimal. A criticality safety analysis shows that the newly designed racks are more subcritical than conventional racks for both regions I and II. The additional reactivity margin yielded by the new integral-type design can be used to reduce the pitch of the rack while maintaining equivalent subcriticality compared to conventional rack design. This study demonstrates the potential of Gd-based neutron absorbers in structure materials for increasing the total amount of fuel assemblies that can be stored in a SF storage pool.

Experimental investigation on RCCI heat transfer in a light-duty diesel engine with different fuels: Comparison versus conventional diesel combustion

Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide range of operating conditions. The high thermal efficiency of RCCI is explained by the combination of a short-duration and well-phased combustion process, which maximizes the fuel-to-work conversion efficiency, together with relatively low combustion temperatures, which increases the specific heat ratio during expansion and reduces thermal gradients for heat transfer losses. The objective of this work is to study the RCCI heat transfer characteristics and compare them to those of the CDC regime. To do this, a single-cylinder light-duty research engine instrumented with 25 K-type thermocouples distributed among the cylinder head and cylinder liner is used. First, the influence of some engine settings on the RCCI heat transfer phenomenon is explored by means of parametric sweeps. Later, the RCCI heat transfer characteristics are compared for two different low reactivity fuels (LRF), gasoline and E85. Finally, the heat transfer characteristics of RCCI and CDC combustion regimes are compared at some representative operating points in matched load conditions. The results show that both LRF tested are suitable to be used in RCCI giving similar results in terms of energy usage. Moreover, the ability of RCCI combustion in exploiting the fuel energy to extract useful work is demonstrated, reducing by 13% the heat transfer versus CDC.

Properties and Pulverized Coal Combustion of Low-Reactivity Fuels. Part II. Furnace and Burner Equipment1

In case of the low volatile content and low heat of combustion of the volatile matter, external factors play a more important role in stabilization of the flame, than in the case of reactive coals. The paper offers a review of solutions for improving the design of the swirl burners, their arrangement and furnace layout.

Concept of Stationary Wave Reactor with Rotational Fuel Shuffling

In the breed and burn (B&B) strategy, low-reactivity fuels are loaded in a core. It is difficult to keep criticality in operating a small core. To enhance the potential for achieving criticality, the neutron economy in a core should be improved. One improvement method is to increase the core size and reduce neutron leakage. If it is necessary to avoid the large-sized core, another method is to locate high-reactivity fuels in high-neutron-importance region continuously through an equilibrium burnup state. On the other hand, to stabilize the change of neutron flux and power distribution during the operation, the B&B regions need to be kept stationary in the same region.In this study, a rotational fuel-shuffling concept was proposed. In this concept, fuel assemblies are moved to the next position step by step in a divided symmetry core region. Fresh fuel is loaded from the periphery and moved toward the center region, then moved outward and discharged. If the core could achieve an equilibrium state at which high-reactivity fuels are continuously placed in the core center region, it would be possible to keep the B&B regions stationary. In this kind of equilibrium state, high-reactivity fuels are placed in high-neutron-importance region stably. Simulations for this concept were performed using the continuous-energy Monte Carlo code MVP/MVP-BURN. A small lead-bismuth-cooled fast reactor with metallic fuel was adopted as the core design. As a result, a core with rotational fuel shuffling achieved an equilibrium cycle at criticality, and the change of multiplication factors in the equilibrium cycle was less than 0.1%. The neutron flux and power distributions were almost unchanged during the operation. In addition, high-reactivity fuels were constantly placed in the high-neutron-flux region. It was found that this concept can achieve criticality and a stable power profile.

Fuel consumption and engine-out emissions estimations of a light-duty engine running in dual-mode RCCI/CDC with different fuels and driving cycles

This work compares the performance and emissions of two dual-mode combustion concepts over different driving cycles by means of vehicle systems simulations. The dual-mode concept relies on switching between the dual-fuel concept known as reactivity controlled compression ignition (RCCI) and conventional diesel combustion (CDC) to cover the whole engine map. The experimental RCCI maps obtained with diesel-E85 and diesel-gasoline used as inputs to perform the simulations were obtained in a high compression ratio light-duty diesel engine (17.1:1) following the same mapping procedure in both cases. The driving cycles simulated to perform the comparison were the Real Driving Emissions cycle (Europe), Worldwide harmonized Light vehicles Test Cycle (Europe), Federal Test Procedure FTP-75 (United States) and JC08 (Japan). The results show that the dual-mode concept has potential to be implemented in flexible-fuel vehicles. Using gasoline as low reactivity fuel (LRF) for RCCI, the vehicle mileage would be equal to CDC, but having reductions in NOx and soot emissions of 16% and 50%, respectively, along the RDE cycle. Using E85 instead of gasoline, the reductions in NOx and soot emissions increase up to 50% and 85%, respectively, but in this case promoting higher thermal efficiency than CDC.

Properties and Pulverized Coal Combustion of Low-Reactivity Fuels. Part I. Fuel Properties and Preparation for Combustion

Low-reactivity properties of anthracite, lean coals, and petroleum coke are determined by a combination of factors, including not only a low heating value of the volatile matter, but also an increase in the volatile yield and ignition temperatures, as well as decrease in reactivity properties of a non-volatile residue. The fuel preparation activities intended to increase the stability of the fuel ignition and burnout include the improvement of heat balance of the air-fuel mixture flow and favorable adjustment of the reactivity properties of the fuel supplied to the furnace.

LTC (low-temperature combustion) analysis of PCCI (premixed charge compression ignition) with n-butanol and cotton seed biodiesel versus combustion and emissions characteristics of their binary mixtures

Abstract Direct injection (DI) of cotton seed biodiesel (CS100) with port fuel injection (PFI) of n-butanol was used for producing Premixed Controlled Compression Ignition (PCCI) to achieve low-temperature combustion (LTC) and obtain lower gaseous emissions in comparison to ULSD#2 (ultra-low sulfur diesel). PFI engine operation was compared to the combustion of binary mixtures of the same fuels reflecting the same weight ratio of high reactivity (CS100) and low reactivity (n-butanol) fuels. The supercharged engine was operated at constant speed and load with 20% exhaust gas recirculation (EGR). When compared to ULSD#2 reference, the ignition delay of 50% n-butanol and 50% CS100 binary mixture increased by 12% while the 50% n-butanol PFI with 50% CS100 DI led to a 17% decrease in ignition delay. Emissions of soot and nitrogen oxides were simultaneously improved using the PCCI strategy, reducing by 84% and 17%, respectively, given lower peak in-cylinder temperatures and increased oxygenation of the mixture. Carbon monoxide (CO) and unburned hydrocarbons (UHC) increased by several orders of magnitude as a downside of dual fuel injection; ringing intensity, however, improved, decreasing by 30% when using 50% n-butanol PFI in comparison to the ULSD#2 baseline given a smoother pressure gradients. Energy specific fuel consumption for CS50Bu50 (50% ULSD-50% n-butanol blend) increased by 4.5% compared to ULSD#2. The mechanical efficiencies and the coefficient of variation (COV) of IMEP were maintained at 70% and 2.5% respectively, during PCCI, indicating stable operation with renewable fuels.

Simultaneous particulate matter and nitrogen oxide emission reduction through enhanced charge homogenization in diesel engines

In the presented study, low temperature combustion was established with a direct injection of diesel fuel being a representative of high reactivity fuels and tire pyrolysis oil being a representative of low reactivity fuels. Tire pyrolysis oil was tested as a potential waste derived fuel for low temperature combustion, as it features diesel-like physical properties and lower cetane number compared to diesel fuel. The goal of this study was determination of suitable injection strategies and exhaust gas re-circulation rates to explore potentials of both fuels in reducing emissions in low temperature combustion modes. It was demonstrated that relatively small changes in the engine control strategy possess the potential to significantly improve NOx/particulate matter trade-off with minor effect on engine efficiency. In addition, low temperature combustion was for the first time successfully demonstrated with tire pyrolysis oil fuel, however, it was shown that lower re-activity of the fuel is by itself not sufficient to improve NOx /soot trade-off compared to the diesel fuel as entire spectra of fuel properties play an important role in improving NOx /soot trade-off. This study thus establishes relations between different engine control strategies, intake manifold pressure and exhaust gas recirculation rate on engine thermodynamic parameters and engine-out emissions while utilizing innovative waste derived fuel that have not yet been analysed in similar combustion concepts.

Isolating the effects of reactivity stratification in reactivity-controlled compression ignition with iso-octane and n-heptane on a light-duty multi-cylinder engine

Reactivity-controlled compression ignition (RCCI) is a dual-fuel variant of low-temperature combustion that uses in-cylinder fuel stratification to control the rate of reactions occurring during combustion. Using fuels of varying reactivity (autoignition propensity), gradients of reactivity can be established within the charge, allowing for control over combustion phasing and duration for high efficiency while achieving low NOx and soot emissions. In practice, this is typically accomplished by premixing a low-reactivity fuel, such as gasoline, with early port or direct injection, and by direct injecting a high-reactivity fuel, such as diesel, at an intermediate timing before top dead center. Both the relative quantity and the timing of the injection(s) of high-reactivity fuel can be used to tailor the combustion process and thereby the efficiency and emissions under RCCI. While many combinations of high- and low-reactivity fuels have been successfully demonstrated to enable RCCI, there is a lack of fundamental understanding of what properties, chemical or physical, are most important or desirable for extending operation to both lower and higher loads and reducing emissions of unreacted fuel and CO. This is partly due to the fact that important variables such as temperature, equivalence ratio, and reactivity change simultaneously in both a local and a global sense with changes in the injection of the high-reactivity fuel. This study uses primary reference fuels iso-octane and n-heptane, which have similar physical properties but much different autoignition properties, to create both external and in-cylinder fuel blends that allow for the effects of reactivity stratification to be isolated and quantified. This study is part of a collaborative effort with researchers at Sandia National Laboratories who are investigating the same fuels and conditions of interest in an optical engine. This collaboration aims to improve our fundamental understanding of what fuel properties are required to further develop advanced combustion modes.

Dilution Sensitivity of Particulate Matter Emissions From Reactivity-Controlled Compression Ignition Combustion

Dual-fuel reactivity-controlled compression ignition (RCCI) combustion can yield high thermal efficiency and simultaneously low NOx and soot emissions. Although soot emissions from RCCI are very low, hydrocarbon (HC) emissions are high, potentially resulting in higher than desired total particulate matter (PM) mass and number caused by semivolatile species converting the particle phase upon primary dilution in the exhaust plume. Such high organic fraction PM is known to be highly sensitive to dilution conditions used when collecting samples on a filter or when measuring particle number using particle sizing instruments. In this study, PM emissions from a modified single-cylinder diesel engine operating in RCCI and conventional diesel combustion (CDC) modes were investigated under controlled dilution conditions. To investigate the effect of the fumigated fuel on the PM emissions, 150 proof hydrous ethanol and gasoline were used as low reactivity fuels. The data reveal that PM from RCCI combustion is more sensitive to the variation of dilution conditions than PM from single fuel conventional diesel combustion. RCCI PM primarily consisted of semivolatile organic compounds and a smaller amount of solid carbonaceous particles. The fumigated fuel had a significant effect on PM emissions' characteristics for RCCI combustion. Hydrous ethanol fueled RCCI PM contained a larger fraction of volatile materials and was more sensitive to the variation of dilution conditions compared to the gasoline fueled RCCI mode.

Evaluating the reactivity controlled compression ignition operating range limits in a high-compression ratio medium-duty diesel engine fueled with biodiesel and ethanol

This work investigates the load limits of reactivity controlled compression ignition combustion, a dual-fuel concept which combines port fuel injection of low-reactivity fuels with direct injection...

Combustion and ignition characteristics of ammonia/air mixtures in a micro flow reactor with a controlled temperature profile

Combustion and ignition characteristics of a stoichiometric ammonia/air mixture were investigated by a micro flow reactor with a controlled temperature profile from ambient temperature to 1300K at atmospheric pressure. Three kinds of flame dynamics depending on inlet mean flow velocities, namely, normal flames in the high velocity regime, flames with repetitive extinction and ignition (FREI) in the intermediate velocity regime, and weak flames in the low velocity regime, which have also been observed for hydrocarbons in previous studies, were observed for ammonia by the direct observation with a digital still camera in this study. The existence of ammonia weak flames at 1270K was confirmed. Special attention was paid to weak flames to examine ignition characteristics of an ammonia/air mixture at low temperature because ignition experiments of ammonia have been conducted only at very high temperatures (around 2000K). Species measurement for a stoichiometric ammonia/air weak flame at 10cm/s was made using and a mass spectrometer and a T-shaped reactor fused with a micro-probe. The present species measurement elucidated the structure of the ammonia/air weak flame and complete combustion was confirmed at 1290K. Five reaction mechanisms were used for computations of weak flames and the four of them did not predict complete combustion within the given computational domain. One reaction mechanism predicted complete combustion but the weak flame position in computation was located in a temperature region lower than that in the experiment. The order of reactivity evaluations among the five mechanisms using weak flames in the micro flow reactor agreed with that using ignition delay times at low temperatures which are generally difficult to be taken by ignition experiments. The capability of weak flame methodology to validate ignition properties of reaction mechanisms for low reactivity fuels like ammonia was successfully demonstrated in this study.

Enabling dual fuel sequential combustion using port fuel injection of high reactivity fuel combined with direct injection of low reactivity fuels

This paper presents a preliminary experimental study on the combustion and emission characteristics of Dual Fuel Sequential Combustion (DFSC) mode, in which port fuel injection of n-heptane combined with in-cylinder, directly injected ethanol, n-butanol and n-amyl alcohol are used in a single-cylinder engine at fixed directly injection timing. The results show that the heat release can be divided mainly into three stages: low temperature reaction, high temperature reaction of n-heptane and the directly injected fuel combustion stage. The amount of port injected n-heptane plays a key role in the maximum in-cylinder pressure (Pmax), maximum in-cylinder mass averaged temperature (Tmax) and the maximum pressure rise rate. For the high overall lower heating values (LHVs) per-cycle, the CO emissions decrease with the increase of the premixed ratio. By contrast, the CO emissions increase with the premixed ratio when the overall LHVs per-cycle are kept at medium and low levels. The NOx and soot emissions are all kept at low levels for the experimental conditions. In particular, the higher latent heat, lower cetane values and the shorter carbon chains associated with ethanol lead to lower NOx and soot emissions than those of n-butanol and n-amyl alcohol. When directly injection of n-butanol and at low loads, with optimized premixed ratio, the indicated thermal efficiency can be higher than 46% meanwhile maintaining low emissions.

Investigation of Performance and Emission Characteristics using Low Reactivity Fuel and Biodiesel Blended Nanoparticles in Diesel Engine

Investigation of Performance and Emission Characteristics using Low Reactivity Fuel and Biodiesel Blended Nanoparticles in Diesel Engine

Effects of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions in a heavy-duty diesel engine

This work investigates the effect of low reactivity fuel characteristics and blending ratio on low load RCCI (reactivity controlled compression ignition) performance and emissions using four different low reactivity fuels: E10-95, E10-98, E20-95 and E85 (port fuel injected) while keeping constant the same high reactivity fuel: diesel B7 (direct injected). The experiments were conducted using a heavy-duty single-cylinder research diesel engine adapted for dual fuel operation. All tests were carried out at 1200 rev/min and constant CA50 of 5 CAD ATDC. For this purpose, the premixed energy was equal for the different blends and the EGR (exhaust gas recirculation) rate was modified as required, keeping constant the rest of engine settings. In addition, a detailed analysis of air/fuel mixing process has been developed by means of a 1-D spray model.Results suggest that in-cylinder fuel reactivity gradients strongly affect the engine efficiency at low load. Specifically, a reduced reactivity gradient allows an improvement of 4.5% in terms of gross indicated efficiency when the proper blending ratio is used. In addition, EURO VI NOx and soot emission levels are fulfilled with a strong reduction in CO and HC compared with the case of the higher reactivity gradient among the low and high reactivity fuel.

Effects of fuel ratio and injection timing on gasoline/biodiesel fueled RCCI engine: A modeling study

RCCI (reactivity controlled compression ignition) has drawn much attention since it was proposed, as it could lead to high performance and clean combustion. The original concept of an RCCI engine is to use gasoline and diesel as the low and high reactivity fuels, respectively. In this study, biodiesel is considered as a substitute of diesel. Hence, research was numerically conducted on a gasoline/biodiesel fueled RCCI engine. To simulate the combustion process, coupled KIVA4–CHEMKIN was used. The gasoline/biodiesel reaction mechanism as implemented in the code was developed by the authors. Two major factors, namely gasoline to total input energy ratio and SOI (start of injection) timing, have been considered. The varied gasoline energy ratios were applied to both C-SOI (conventional SOI) and A-SOI (advanced SOI) timings. Comparing the combustion characteristics between two SOI timings with varied gasoline energy ratios, it is found that A-SOI could offer more controllability on start of combustion, combustion phasing etc. when varying gasoline ratio. As for the emissions formation, increases in gasoline could reduce NOx and soot emissions simultaneously by achieving more homogeneous combustion. However, the designed spray angle of 78° for C-SOI, when used with A-SOI, would increase the soot formation especially when more biodiesel is injected.

Effects of direct injection timing and blending ratio on RCCI combustion with different low reactivity fuels

This work investigates the effects of the direct injection timing and blending ratio on RCCI performance and engine-out emissions at different engine loads using four low reactivity fuels: E10-95, E10-98, E20-95 and E85 (port fuel injected) and keeping constant the same high reactivity fuel: diesel B7 (direct injected). The experiments were conducted using a heavy-duty single-cylinder research diesel engine adapted for dual-fuel operation. All the tests were carried out at 1200rpm. To assess the blending ratio effect, the total energy delivered to the cylinder coming from the low reactivity fuel was kept constant for the different fuel blends investigated by adjusting the low reactivity fuel mass as required in each case. In addition, a detailed analysis of the air/fuel mixing process has been developed by means of a 1-D in-house developed spray model.Results suggest that notable higher diesel amount is required to achieve a stable combustion using E85. This fact leads to higher NOx levels and unacceptable ringing intensity. By contrast, EURO VI NOx and soot levels are fulfilled with E20-95, E10-98 and E10-95. Finally, the higher reactivity of E10-95 results in a significant reduction in CO and HC emissions, mainly at low load.

Isobutanol as Both Low Reactivity and High Reactivity Fuels with Addition of Di-Tert Butyl Peroxide (DTBP) in RCCI Combustion

Isobutanol as Both Low Reactivity and High Reactivity Fuels with Addition of Di-Tert Butyl Peroxide (DTBP) in RCCI Combustion