Direct Dual Fuel Research Articles

Impact of spray interaction on ammonia/diesel dual-fuel combustion and emission under engine relevant conditions

This study investigates the combustion characteristics of ammonia and diesel sprays in a constant-volume vessel under conditions typical of internal combustion engines, focusing on the interplay between evaporation dynamics and flame interactions within the framework of the Direct Dual Fuel Stratification (DDFS) concept. Under non-evaporation conditions, ammonia and diesel sprays exhibit comparable evaporation profiles, but under evaporation scenarios, ammonia’s higher evaporation rate results in faster mixing with ambient gas than diesel despite the similar liquid penetration lengths of these two fuels. By utilizing meticulously designed arrangements of diesel and ammonia spray injectors, two distinct interaction scenarios between diesel spray and ammonia spray, early and late interaction, are explored. In the early interaction scenario, fuel-rich ammonia-air mixtures ignite directly by the diesel flame, achieving self-sustained propagation and significant heat release, thereby maintaining a high-temperature region for continuous combustion. Conversely, in late interaction scenarios, rapid ammonia evaporation leads to a fuel-lean ammonia/air mixture that cannot be ignited by the diesel flame, eventually leading to ammonia flame extinction. The study reveals that NOx and N2O emissions are sensitive to the diesel/ammonia flame interaction. N2O emissions, formed predominantly at the forefront of the quenching ammonia flame, pose a significant challenge due to the fast evaporation rate and slow oxidation rate in fuel-lean mixtures. These findings provide insights into the physics of ammonia–diesel combustion, highlighting the challenges and potential strategies for efficient and clean combustion in ammonia-fueled DDFS engines.

Investigative research of diesel/ethanol advanced combustion strategies: A comparison of Premixed Charge Compression Ignition (PCCI) and Direct Dual Fuel Stratification (DDFS)

Direct Dual Fuel Stratification (DDFS) is a new low-temperature combustion (LTC) approach that employs dual fuel direct injection in the combustion chamber. In this method, a relatively small proportion of diesel fuel was pre-injected and utilized to activate the burning of the premixed charge followed by direct injection of a diesel/ethanol mixture (75% diesel, 25% ethanol by volume) into the combustion chamber near TDC. The DDFS approach generates a lower reactivity charge in the central sector of the combustion chamber and a stronger reactivity charge along the wall. For the examination of combustion vibrations and acoustic, a new technique dependent on the fast Fourier transform (FFT) of the cylinder vibration statistics was used. Whereas the PCCI combustion technique is more likely to cause knocking than the typical diesel CI, the results show that charge stratification in DDFS combustion does have a good effect in reducing vibration intensity. Owing to the improved controllability of the start of combustion and burning period, DDFS combustion attained a brake thermal efficiency (BTE) of 51%, which was larger than CI and PCCI. DDFS shows ultra-low nitrogen oxide (NOx) (below 1 g/kW-h), mild carbon monoxide (CO) (below 6 g/kW-h), and unburned hydrocarbons (UHC) emissions. Because of the higher thermal efficiency and a decreased carbon source due to presence of ethanol, DFFS combustion could produce lower CO levels by up to 34% when compared to PCCI.

Multiple-Objective Optimization Of Direct Dual Fuel Stratification (Ddfs) Combustion at Different Loads

Multiple-Objective Optimization Of Direct Dual Fuel Stratification (Ddfs) Combustion at Different Loads

Optimization of the exergy efficiency, exergy destruction, and engine noise index in an engine with two direct injectors using NSGA-II and artificial neural network

Direct Dual Fuel Stratification (DDFS) strategy is a novel Low Temperature Combustion (LTC) strategy that has comparable thermal efficiency to the Reactivity Controlled Compression Ignition (RCCI) strategy, while it offers more control over the combustion process and the rate of heat release. The DDFS strategy uses two direct injectors for the low- and high-reactivity fuels (gasoline and diesel) to benefit from the RCCI concept. In this study, the injection strategy of the injectors of a gasoline/diesel DDFS engine was optimized from the thermodynamic perspective to maximize exergy efficiency and minimize exergy destruction and an engine noise index. An artificial neural network was developed with 576 samples from a CFD code to predict the DDFS mode behavior, and the non-dominated sorting genetic algorithm (NSGA-II) was used to obtain the Pareto Front and the optimal solutions. Compared to the base case, the exergy efficiency of the optimal cases increased by up to 2%, exergy destruction and Peak Pressure Rise Rate (PPRR) reduced by about 2.3%, and 2 bar/deg, respectively, in the optimal solutions. NOX and soot emissions were reduced by 40% and 35%, respectively, in the best-case scenarios.

Meeting EURO6 emission regulations by multi-objective optimization of the injection strategy of two direct injectors in a DDFS engine

Direct Dual Fuel Stratification (DDFS) is a novel LTC strategy among other strategies which uses two direct injectors in the combustion chamber, similar to Reactivity-Controlled Compression Ignition (RCCI), but resulting in more authority over the combustion process and the rate of heat release. DDFS has comparable thermal efficiency to RCCI and HCCI, as well as extra-low NOx and soot emissions, and it also is able to meet the EURO6 emission mandate without using aftertreatment under optimized conditions. Thus, it is crucial to optimize the injection strategy of both injectors in a DDFS engine. Artificial Neural Networks (ANNs) are used to develop a model for predicting engine performances and pollution. A multi-objective optimization analysis was performed to minimize NOX, soot and fuel consumption simultaneously using the non-dominated sorting genetic algorithm (NSGA-II) for the injection parameters of the gasoline and diesel direct injectors. The optimal solutions met the EURO6 mandate for NOX and soot, offered lower fuel consumption up to 8 g/kW-h, and also had about 2% higher thermal efficiency than the base case. Thermodynamic evaluation based on the first and second laws were performed for seven selected candidates on the Pareto Front and compared with the base case.

Numerical Analysis of the Effects of Direct Dual Fuel Injection on the Compression Ignition Engine.

In this work, the influence of direct dual fuel injection on a compression ignition engine fueled with gasoline and diesel has been investigated. To do this, closed cycle combustion simulations have been performed. Gasoline has been supplied through port injection and early direct and late direct injection to achieve fuel stratification and emission reduction. Simulations have been done for various start of injection (SOI) timings of diesel fuel. A detailed discussion on a low temperature heat release (LTHR) mechanism has been done. Results revealed that the maximum gross indicated thermal efficiency (GITE) of 39% is obtained for port injection of gasoline mode. Direct dual fuel combustion (type 2) (DDC2) mode shows approximately 2% and 38% less GITE and oxides of nitrogen (NOx), respectively, and 40% more soot as compared to the port injection gasoline mode. DDC2 mode shows lower oxides of carbon and hydrocarbon emissions as compared to other dual fuel modes. More than 99% of combustion efficiency and less maximum pressure rise rate have been noticed in the DDC2 case. Strong LTHR and high temperature premixed combustion region have been found in advanced SOI timing cases (in DDC2). In-cylinder contours for the DDC2 case show that diesel and gasoline fuels combusted successively cause less in-cylinder temperature than that for the conventional dual fuel combustion case.

A study of using E10 and E85 under direct dual fuel stratification (DDFS) strategy: Exploring the effects of the reactivity-stratification and diffusion-limited injection on emissions and performance in an E10/diesel DDFS engine

One promising pathway to directly control combustion is Direct Dual Fuel Stratification (DDFS). DDFS has comparable thermal efficiency to RCCI, acceptable levels of emissions, and lower cyclic variation. The primary drawback of DDFS is soot production owing to the diffusion-limited nature of the near-TDC injection. In this paper, E10 (10% ethanol in gasoline by volume) and E85 were studied as alternative fuels to gasoline to tackle soot formation. In the first step, E10 and E85 were compared, and the best alternative to gasoline was chosen based on emissions and performance. E10 reduced soot by 40%, and E85 eradicated soot completely. However, E85 had 25 times higher NOX than gasoline. Next, diesel energy fraction and its start of injection (SOI2) were swept to explore the domain of the reactivity controlled regime. It was found that for SOI2s before −80° ATDC, the regime was premixed, and for SOI2s after −40° ATDC, the regime was diffusion-limited. Diesel energy fractions, more than 11%, yielded unintended combustion. Then, the energy fraction and injection timing of the near-TDC injection (SOI3) was swept and studied. The best domain for both injectors was discovered based on the EURO6 emission mandate. Spray angles of both injectors were swept from 50 to 80°, and 55° for diesel injector and 65° for the E10 injector showed the best results regarding emissions, performance, and fuel consumption. Finally, the effects of the injection pressure of SOI3 on emissions and performance were studied. The suitable domain for injection pressure was chosen based on EURO6.

An Investigation of the Effects of the Piston Bowl Geometries of a Heavy-Duty Engine on Performance and Emissions Using Direct Dual Fuel Stratification Strategy, and Proposing Two New Piston Profiles

An Investigation of the Effects of the Piston Bowl Geometries of a Heavy-Duty Engine on Performance and Emissions Using Direct Dual Fuel Stratification Strategy, and Proposing Two New Piston Profiles

Exploring the Role of Reactivity Gradients in Direct Dual Fuel Stratification

Exploring the Role of Reactivity Gradients in Direct Dual Fuel Stratification

Direct Dual Fuel Stratification, a Path to Combine the Benefits of RCCI and PPC

Direct Dual Fuel Stratification, a Path to Combine the Benefits of RCCI and PPC