High Reactivity Fuels Research Articles

Large-eddy simulation of tri-fuel ignition: diesel spray-assisted ignition of lean hydrogen–methane–air mixtures

We present 3D numerical results on tri-fuel (TF) combustion using large-eddy simulation and finite rate chemistry. The TF concept was recently introduced by Karimkashi et al. (Int. J. Hydrogen Energy, 2020) in 0D. Here, the focus is on spray-assisted ignition of methane–hydrogen blends. The spray acts as a high-reactivity fuel (HRF) while the ambient premixed methane-hydrogen blend acts as a low-reactivity fuel (LRF) mixture. Better understanding on such a TF process could enable and motivate more extensive hydrogen usage in e.g. compression ignition marine engines where spray-assisted dual-fuel (DF) combustion is already utilised. The studied spray set-up is based on the modified ECN Spray A case, see Kahila et al. (Combustion and Flame, 2019) for DF combustion. The ambient pressure and temperature are 900 K and 60 bar. The hydrogen content of the LRF blend is varied systematically by changing the molar fraction , . The main added value of the study is that we extend the TF concept to 3D. The particular findings of the study are as follows: 1) Consistent with Karimkashi et al. 2020, hydrogen delays ignition also in 3D and the effect becomes significant for . 2) The ratio between the first- and second-stage ignition delay times and . Furthermore, the ratio between 3D and 0D ignition delay times is given as for all TF cases. 3) Finally, consistent with Karimkashi et al. 2020, also in 3D the high-temperature combustion heat release mode is shown to appear stronger in TF than the low-temperature combustion mode compared to DF methane–diesel combustion.

Effect of CNG and CBG as low reactivity fuels along with diesel and TPME as high reactivity fuels in RCCI mode of combustion by varying different loads

• Thevetia peruviana is a renewable fuel. • Brake thermal efficiency increases as the load increases. • RCCI is one of the most efficient low temperature combustion strategy. • RCCI engine powered with CNG exhibits higher BTE. In the present work, an effort is carried out to study the effect of load extension in reactivity controlled compression ignition (RCCI) mode of combustion. Compressed natural gas (CNG) and compressed biogas (CBG) are used as low reactivity fuels. Diesel and different blends of thevetia peruviana methyl ester (TPME) are used as high reactivity fuels. The whole experimentation is carried out at 50% and 75% of the rated power. Results showed that RCCI engine operated at 75% load gives higher brake thermal efficiency (BTE) about 29.74% and higher nitric oxide (NOx) emissions along with lower carbon monoxide (CO), hydrocarbon (HC) and smoke emissions. Among various fuel combinations tested D + CNG gives better results in terms of performance and emission characteristics.

Emission reduction in diesel engine with acetylene gas and biodiesel using inlet manifold injection

It is well known that acetylene has a wide flammability and is readily available and low-cost non-crude oil derivative fuel. According to the property of low motor octane number, the acetylene cannot be used alone in the internal combustion engine. Research has shown that the introduction of biodiesel results in a substantial reduction in the use of conventional fossil fuels and also in the amount of emissions. This study focuses on performance improvement and emission reduction of conventional diesel engine using acetylene gas as a low-reactivity fuel (LRF) and B20 mahua biodiesel as a high-reactivity fuel (HRF) in the reactivity controlled compression ignition (RCCI) mode. The computational fluid dynamics (CFD) principle is used to evaluate the optimal angle of the LRF injector to achieve better fluid flow mixing pattern in the inlet manifold. From the CFD simulation, an optimal LRF injection angle of 45° is defined in the intake manifold. The modified intake manifold engine is tested for performance, emission and combustion characteristics at different flow rates of acetylene through the injector. It is observed that the brake thermal efficiency (BTE) is increased by about 3.7% at a flow rate of 4 liters per minute (LPM) of acetylene injection in RCCI combustion mode compared to conventional biodiesel operation and significant decreases in polluting components such as smoke opacity, oxides of nitrogen (NOx), hydrocarbon (HC) and carbon monoxide (CO) are reduced by about 10%, 7.6%, 13.4% and 28.7%.

Impact of secondary fuel injector in various distance on direct injection diesel engine using acetylene-bio diesel in reactivity controlled compression ignition mode

ABSTRACT Many researchers utilized acetylene fuel in conventional diesel engine in dual fuel mode. Dual fuel Reactivity Controlled Compression Ignition (RCCI) engine is established by modifying the Conventional Diesel Engine (CDE) intake manifold that supplies secondary fuel through the injector. The aim of the study is to analyze the acetylene-bio diesel fueled RCCI engine by varying the secondary fuel injector position in the intake manifold. The experiment was carried out by acetylene gas as a Low Reactivity Fuel (LRF) which is supplied by an injector at a distance of 243.5 mm, 288.5 mm, and 333.5 mm from the intake valve with a constant flow rate of 4 l/min during the suction stroke. The High Reactivity Fuel (HRF) B20 MOME (Mahua Oil Methyl Ester) is supplied through the injector at end of the compression stroke. The modified engine was tested for its performance, combustion, and emission characteristics. The result shows that the Brake Thermal Efficiency (BTE) at a distance of 243.5 mm from the intake valve increases all loads and achieves a brake thermal efficiency improvement of 2.27% from the B20 MOME fueled engine. The Exhaust Gas Temperature (EGT) and NOx, which are predominantly higher in biodiesel fueled engine, are reduced about 13.5% and 13.6% respectively at a distance of 243.5 mm from the intake valve in the RCCI mode combustion.

Evaluation of comparative engine combustion, performance and emission characteristics of low temperature combustion (PCCI and RCCI) modes

In this study, a comparative investigation of engine combustion, performance and emission characteristics of low temperature combustion modes namely premixed charge compression ignition (PCCI) and reactivity controlled compression ignition (RCCI) with conventional compression ignition (CI) combustion mode was performed. Experiments were performed in a single cylinder research engine at constant engine speed (1500 rpm) and at four different engine loads (1, 2, 3 and 4 bar brake mean effective pressure (BMEP)). Baseline CI and PCCI mode combustion experiments were performed using mineral diesel as test fuel; while mineral diesel-methanol fuel pair was used as high-reactivity fuel (HRF) and low-reactivity fuel (LRF) respectively in RCCI mode combustion. Results showed that RCCI mode combustion was relatively more stable compared to baseline CI and PCCI combustion modes. At higher engine loads, RCCI mode combustion exhibited relatively lower knocking and combustion noise than other combustion modes. Performance characteristics showed that brake thermal efficiency (BTE) of RCCI mode combustion was comparable to baseline CI mode combustion, however, at higher engine loads, RCCI mode combustion resulted in relatively higher BTE compared to both baseline CI and PCCI combustion modes. Significantly lower EGT of RCCI mode combustion compared to baseline CI as well as PCCI combustion modes was another important finding of this study. Emission results showed that RCCI mode combustion emitted relatively lower oxides of nitrogen (NOx), but significantly higher hydrocarbons (HC) compared to baseline CI and PCCI combustion modes. A NOx-BTE trade-off analysis was also carried out, which demonstrated the suitability of RCCI mode combustion at all engine loads. Finally, a parametric analysis was carried out to compare the critical parameters of baseline CI, PCCI, and RCCI combustion modes at low and high engine loads, which exhibited improved engine performance and emission characteristics of low temperature combustion (LTC) modes, especially the RCCI mode combustion.

Experimental Study of the Effect of Start of Injection and Blend Ratio on Single Fuel Reformate RCCI

Abstract A new concept of single fuel reactivity-controlled compression ignition (RCCI) has been proposed through the catalytic partial oxidation (CPOX) reformation of diesel fuel. The reformed fuel mixture is then used as the low reactivity fuel and diesel itself is used as the high reactivity fuel. In this paper, two reformate mixtures from the reformation of diesel were selected for further analysis. Each reformate fuel mixture contained a significant fraction of inert gases (89% and 81%). The effects of the difference in the molar concentrations of the reformate mixtures were studied by experimenting with diesel as the direct injected fuel in RCCI over a varying start of injection timings and different blend ratios (i.e., the fraction of low and high reactivity fuels). The reformate mixture with the lower inert gas concentration had earlier combustion phasing and shorter combustion duration at any given diesel start of injection timing. The higher reactivity separation between reformate mixture and diesel, compared with gasoline and diesel, causes the combustion phasing of reformate-diesel RCCI to be more sensitive to the start of injection timing. The maximum combustion efficiency was found at a CA50 before top dead center (TDC), whereas the maximum thermal efficiency occurs at a CA50 after TDC. The range of energy-based blend ratios in which reformate-diesel RCCI is possible is between 25% and 45%, limited by ringing intensity (RI) at the low limit of blend ratios, and coefficient of variance (COV) of net indicated mean effective pressure (IMEPn) and combustion efficiency at the high limit. Intake boosting becomes necessary due to the oxygen deficiency caused by the low energy density of the reformate mixtures as it displaces intake air.

Exploration of suitable injector configuration for dual-mode dual-fuel engine with diesel and OMEx as high reactivity fuels

Dual-mode dual-fuel (DMDF) combustion stands over other low temperature combustion strategies as it is able to operate over the entire engine map by transitioning between reactivity controlled compression ignition and diffusive combustion depending on the engine load. In combination with non-sooting e-fuels, it is able to achieve low NOx and soot levels even at high loads. Oxygenated fuels like poly-oxymethylene dimethyl ethers (OMEx) have been already proved to present an outstanding NOx-Soot trade-off improvement when used in combination with a DMDF combustion strategy. One drawback of OMEx is that, despite having a high reactivity, it has a low lower heating value, which requires considerably longer injection events compared to other traditional fuels in order to achieve the same engine power output. The long injections limit the flexibility of the injection strategy and result in extremely long combustion durations. A possible solution to this problem resides in moving towards injectors with higher flow rate capacities, but this may compromise the mixing and combustion processes. This work aims to shed some light on the implications of changing the engine hardware to overcome this limitation by testing a DMDF multi-cylinder engine using gasoline as the low-reactivity fuel and diesel or OMEx as the high reactivity fuels with injectors of different flow capacity. The results show that a concise analysis of the involved phenomenology of the combustion process allows to find out the trade-off between the engine-out emissions and the mixing capacity of the injection system while the engine performance is not significantly affected.

Effect of Fuel Injection Pressure and Premixed Ratio on Mineral Diesel-Methanol Fueled Reactivity Controlled Compression Ignition Mode Combustion Engine

Abstract Reactivity controlled compression ignition (RCCI) mode combustion has attracted significant attention because of its superior engine performance and significantly lower emissions of oxides of nitrogen (NOx) and particulate matter (PM) compared with conventional compression ignition (CI) mode combustion engines. In this experimental study, effects of fuel injection pressure (FIP) of high reactivity fuel (HRF) and premixed ratio of low reactivity fuel (LRF) were evaluated on a diesel-methanol fueled RCCI mode combustion engine. Experiments were performed in a single cylinder research engine at a constant engine speed (1500 rpm) and constant engine load (3 bar BMEP) using three different FIPs (500, 750, and 1000 bar) of mineral diesel and four different premixed ratios (rp = 0, 0.25, 0.50, and 0.75) of methanol. Results showed that RCCI mode resulted in more stable combustion compared with baseline CI mode combustion. Increasing FIP resulted in relatively higher knocking, but it reduced with increasing premixed ratio. Relatively higher brake thermal efficiency (BTE) of RCCI mode combustion compared with baseline CI mode combustion is an important finding of this study. BTE increased with increasing FIP of mineral diesel and increasing premixed ratio of methanol. Relatively dominant effect of increasing FIP on BTE at higher premixed ratios of methanol was also an important finding of this study. RCCI mode combustion resulted in higher carbon monoxide (CO) and hydrocarbon (HC) emissions, but lower PM and NOx emissions compared with baseline CI mode combustion. Increasing FIP of HRF at lower premixed ratios reduced the number concentration of particles; however, effect of FIP became less dominant at higher premixed ratios. Relatively higher number emissions of nanoparticles at higher FIPs were observed. Statistical and qualitative correlations exhibited the importance of suitable FIP at different premixed ratios of LRF on emission characteristics of RCCI mode combustion engine.

Effects of an injector cooling jacket on combustion characteristics of compressed-ignition sprays with a gasoline-hydrogenated catalytic biodiesel blend

The fuel properties in Gasoline Combustion ignition modes (GCI) have been adapted by mixing high reactivity fuels for improving poor combustion stability with pure gasoline. Precise control of the injector tip temperature, as well as the fuel temperature, are considered as the essential boundary conditions to conduct the fundamental investigation on combustion process of GCI spray. Therefore, the impacts of an injector cooling jacket on the spray and combustion developments of a mixture contains 60% gasoline and 40% hydrogenated catalytic biodiesel are studied using a constant volume combustion chamber (CVCC) working under GCI mode. A dummy injector is equipped with a thermocouple to measure the effects of the cooling jacket and ambient temperature on tip temperature. The Schlieren imaging and Diffused Background Illumination Extinction Imaging techniques are employed to visualize the reacting spray development and in-flame soot formation. The results illustrate that the injector tip temperature is well-controlled with aiding of the cooling jacket, which only increases by 35 K with increasing ambient temperature by 250 K. Furthermore, it is found from the optical experiments that the liquid length, ignition delay and lift-off length are enlarged for the cooling mode compared to that of the uncooled one. The cooling jacket also brings in a larger overlapping area between liquid length and flame lift-off length. However, the in-flame soot production for the cooling jacket is increased more than twice compared to that of the uncooled one.

A numerical study on combustion mode characterization for locally stratified dual-fuel mixtures

Combustion modes in locally stratified dual-fuel (DF) mixtures are numerically investigated for methanol/n-dodecane blends under engine-relevant pressures. In the studied constant-volume numerical setup, methanol acts as a background low-reactivity fuel (LRF) while n-dodecane serves as high-reactivity fuel (HRF), controlling local ignition delay time. The spatial distribution of n-dodecane is modeled as a sinusoidal function parametrized by stratification amplitude (Y′) and wavelength (0.01 mm<λ<15 mm). In contrast, methanol is assumed to be fully premixed with air at equivalence ratio 0.8. First, one-dimensional setup is investigated by hundreds of chemical kinetics simulations in (Y′, λ) parameter space. Further, the concepts by Sankaran et al. (2005, Proceedings of the Combustion Institute) and Zeldovich (1980, Combustion and Flame) on ignition front propagation speed are applied to develop a theoretical analysis of the time-dependent diffusion–reaction problem. The theoretical analysis predicts two combustion modes, (1) spontaneous ignition and (2) deflagrative propagation, and leads to an analytical expression for the border curve called β-curve herein. One-dimensional chemical kinetics simulations confirm the presence of two combustion modes in (Y′, λ) parameter space while the β-curve explains consistently the position of phase border observed in the simulations. Finally, the role of convective mixing is incorporated to the theoretical expression for the β-curve. The effect of convection on combustion mode is assessed by carrying out two-dimensional fully-resolved simulations with different turbulence levels. Two-dimensional numerical simulation results give evidence on combustion mode switching, which is consistent with predictions of the modified β-curve for turbulent cases. The practical output of the paper is the β-curve which is proposed as a predictive tool to estimate combustion modes for various fuels or fuel combinations.

Numerical study on tri-fuel combustion: Ignition properties of hydrogen-enriched methane-diesel and methanol-diesel mixtures

Simultaneous and interactive combustion of three fuels with differing reactivities is investigated by numerical simulations. In the present study, conventional dual-fuel (DF) ignition phenomena, relevant to DF compression ignition (CI) engines, are extended and explored in tri-fuel (TF) context. In the present TF setup, a low reactivity fuel (LRF), methane or methanol, is perfectly mixed with hydrogen and air to form the primary fuel blend at the lean equivalence ratio of 0.5. Further, such primary fuel blends are ignited by a high-reactivity fuel (HRF), here n-dodecane under conditions similar to HRF spray assisted ignition. Here, ignition is relevant to the HRF containing parts of the tri-fuel mixtures, while flame propagation is assumed to occur in the premixed LRF/H2 containing end gas regions. The role of hydrogen as TF mixture reactivity modulator is explored. Mixing is characterized by n-dodecane mixture fraction ξ, and molar ratio x=XH2XH2+XLRF. When x < 0.6, minor changes are observed for the first- and second-stage ignition delay time (IDT) of tri-fuel compared to dual-fuel blends (x = 0). For methane, when x > 0.6, first- and second-stage IDT increase by factor 1.4–2. For methanol, a respective decrease by factor 1.2–2 is reported. Such contrasting trends for the two LRFs are explained by reaction sensitivity analysis, indicating the importance of OH radical production/consumption in the ignition process. Observations on LRF/H2 end gas laminar flame speed (Sl) indicate that Sl increases with x due to the highly diffusive features of H2. For methane, Sl increase with x is more significant than for methanol.

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.

Effect of Polyoxymethylene Dimethyl Ethers-Diesel Blends as High-Reactivity Fuel in a Dual-Fuel Reactivity Controlled Compression Ignition Combustion

Effect of Polyoxymethylene Dimethyl Ethers-Diesel Blends as High-Reactivity Fuel in a Dual-Fuel Reactivity Controlled Compression Ignition Combustion

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.

Concept of breed and burn reactor with spiral fuel shuffling

A spiral fuel-shuffling scheme was proposed to establish an advantageous neutron-economy breed and burn (B&B) operation mode, in which high-reactivity fuels are placed stably in a region of high neutron importance. To reduce the maximum displacements per atom (dpa) value without a fuel reconditioning process, B&B operation mode with smaller burnup core was also considered as a requirement. In this shuffling scheme, fresh fuel assemblies composed of natural uranium are loaded from the core periphery and moved toward the center along a spiral path, then discharged from the core center. Calculation results found that the core with spiral fuel shuffling achieved an equilibrium state at criticality, and that average burnup of discharged fuel was 115 GWD/t-HM. In this equilibrium state, it was found that high-reactivity fuels were continuously placed in a region of high neutron importance, and maximum dpa value was less than 600 dpa.

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.

Surface stabilized combustion technology: An experimental evaluation of the extent of its fuel-flexibility and pollutant emissions using low and high calorific value fuels

Surface-stabilized combustion (SSC) is a fuel-flexible technology that extends the stability limits of lean premixed systems, while achieving ultra-low emissions of NOx, CO and UHC (unburned hydrocarbons). To evaluate these attributes, the present study quantifies (1) operability characteristics i.e., lean blowoff limit and flashback behavior and (2) pollutant emissions (CO, N2O, NH3, NO and NO2) of a commercial SSC burner when operating at a fixed fire rate on a wide range of fuel compositions. The experimental burner is the Duratherm™ ceramic-fiber burner by Alzeta Corporation. Experiments were carried out with multiple gaseous fuel blends starting with low reactivity biogas blends containing up to 65% CO2 (by volume) balanced with natural gas, and high reactivity fuels such as hydrogen enriched natural gas (HENG) blends. The burner was able to stabilize multiple fuel compositions without requiring any modifications, which attests to the inherent fuel-flexibility of the technology. It was found that the modes of operation and flame stabilization of the SSC burner can be parametrized by the ratio of the speed of the mixture at the surface to its laminar burning velocity. The results affirm low emission operation is attainable on all fuels. In terms of nitrogen species other than oxides of nitrogen, the study found trace levels of N2O and NH3 (<0.1 ppm) emitted during steady state operation. However, the emission of those species can become significant during ignition and near the lean stability limit.

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.

Impact of diesel pilot distribution on the ignition process of a dual fuel medium speed marine engine

Recent emission legislation in the marine sector has emphasized the need to reduce nitrogen oxides (NOx) emissions as well as sulphur emissions. The fulfilment of emission legislation limits with conventional marine diesel oil (MDO) requires complex and expensive aftertreatment systems and in this framework lean burn pilot ignited dual fuel (diesel and natural gas) is revealed as one of the most suitable engine platforms to decrease pollutant formations at its source and therefore to mitigate aftertreatment system requirements. For this reason, an experimental study has been carried out in an 8.8l dual fuel single cylinder Wärtsilä 20DF engine in order to evaluate different diesel equivalence ratio distributions in the combustion chamber and to get a deeper insight into the interaction between the high reactivity (diesel) and the low reactivity (natural gas) fuels during the ignition process. Engine testing has been complemented with diesel spray pattern simulations for a better understanding of local combustion conditions. Results show the importance of local pilot fuel distribution as a way to control combustion phasing and consequently its impact on combustion instability, emissions and knock conditions. Stable combustion with engine-out NOx levels below legislation have been achieved without the need of after-treatment system using appropriate high reactivity fuel (HRF) distribution control.

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.