Dual-fuel Reactivity Controlled Compression Ignition Research Articles

High Load (21 Bar IMEP) Dual Fuel RCCI Combustion Using Dual Direct Injection

Dual-fuel reactivity controlled compression ignition (RCCI) combustion has shown high thermal efficiency and superior controllability with low NOx and soot emissions. However, as in other low temperature combustion (LTC) strategies, the combustion control using low exhaust gas recirculation (EGR) or a high compression ratio at high load conditions has been a challenge. The objective of this work was to examine the efficacy of using dual direct injectors for combustion phasing control of high load RCCI combustion. The present computational work demonstrates that 21 bar gross indicated mean effective pressure (IMEP) RCCI is achievable using dual direct injection. The simulations were done using the KIVA3V-Release 2 code with a discrete multicomponent fuel evaporation model, coupled with sparse analytical Jacobian solver for describing the chemistry of the two fuels (iso-octane and n-heptane). In order to identify an optimum injection strategy a nondominated sorting genetic algorithm II (NSGA II), which is a multiobjective genetic algorithm, was used. The goal of the optimization was to find injection timings and mass splits among the multiple injections that simultaneously minimize the six objectives: soot, nitrogen oxide (NOx), carbon monoxide (CO), unburned hydrocarbon (UHC), indicated specific fuel consumption (ISFC), and ringing intensity. The simulations were performed for a 2.44 liter, heavy-duty engine with a 15:1 compression ratio. The speed was 1800 rev/min and the intake valve closure (IVC) conditions were maintained at 3.42 bar, 90 °C, and 46% EGR. The resulting optimum condition has 12.6 bar/deg peak pressure rise rate, 158 bar maximum pressure, and 48.7% gross indicated thermal efficiency. The NOx, CO, and soot emissions are very low.

Comparison of Low Temperature Combustion Strategies for Advanced Compression Ignition Engines with a Focus on Controllability

In the present study, various low temperature combustion strategies were investigated using single cylinder engine experiments. The combustion strategies that were investigated premix the majority of the fuel and do not require exhaust gas recirculation (EGR) to achieve ultra-low NOx and soot emissions for low- to mid-load engine operation. These types of advanced compression ignition combustion strategies have been shown to have challenges with combustion phasing control. The focus of the study was to compare engine performance and emissions, combustion sensitivity to intake conditions, and the ability to control any observed sensitivity through the fuel injection strategy. Even though these are steady state engine experiments, this will demonstrate a given combustion strategies controllability on a cycle-to-cycle basis. The combustion strategies that were investigated are fully premixed dual-fuel homogeneous charge compression ignition (HCCI), dual-fuel reactivity controlled compression ignition (RCCI), and single-fuel partially premixed combustion (PPC). The baseline operating condition was an engine load representative of a light-duty engine: 5.5 bar gross indicated mean effective pressure (IMEP) and 1500 rev/min. At the baseline operating condition, in which the boundary conditions were chosen to yield near optimal engine performance, all three combustion strategies demonstrated high gross indicated efficiency (∼47%) and ultra-low NOx and soot emissions. By perturbing the intake conditions, it was found that all three combustion strategies display similar combustion phasing sensitivities. Both dual-fuel HCCI and RCCI were able to readily correct the observed sensitivities through the global fuel reactivity with no negative implications on the NOx emissions. However, single-fuel PPC was unable to correct for the observed combustion phasing sensitivity and, in some cases, had negative implications on the NOx emissions.

Numerical study of hydrogen addition to DME/CH4 dual fuel RCCI engine

In this study, the effect of hydrogen addition to DME/CH4 dual-fuel RCCI (Reactivity Controlled Compression Ignition) engine is investigated using three dimensional calculations coupled with chemical kinetics. A new reduced DME (Dimethyl Ether) oxidation mechanism is proposed in this study. With the addition of H2, the ignition time is advanced and the peak cylinder pressure is increased. The addition of hydrogen has a greater effect on the beginning stage of combustion than the later stages of combustion. The CH4 emission is reduced with the addition of H2. However, as the flame does not propagate throughout the charge, the CH4 emission is still high. The CO emission is reduced and most of the remaining CO is produced by the combustion of the premixed CH4. With the addition of hydrogen, NO emission is increased. The simulation shows that the final NOx emissions are significantly determined by the injection strategy and quantity of the pilot fuel during dual fuel operation conditions.

인젝터 특성에 따른 2중 연료의 RCCI 연소에 관한 실험적 연구

Abstract : This study describes the characteristics of combustion and exhaust emission in the special engine applying a fuel reactivity controlled compression ignition (RCCI) concept with two different energizing type (solenoid and piezoelectric) injectors for diesel injection. A diesel-gasoline mixed dual-fuel reactivity controlled compression ignition concept is demonstrated as a promising method to achieve high thermal efficiency and low emission in internal combustion engines for transportation vehicles. For investigating the combustion characteristics of RCCI, engine experiments were performed in a light-duty diesel engine over a range of injection timing and mixing rate of gasoline in mass. It was investigated that by increasing the nozzle hole diameter, increasing the combustion pressure and the net indicated mean effective pressure. NO x and soot can be reduced by advancing start of injection in 84 mixing rate of gasoline in mass. The resulting operation showed that light duty engine could achieve 48 percent net indicated efficiency and 191[g/kW-hr] net indicated specific fuel consumption with lower levels of nitrogen oxides and soot.

MODELING CHARGE PREPARATION AND COMBUSTION IN DIESEL FUEL, ETHANOL, AND DUAL-FUEL PCCI ENGINES

In this work, multi-dimensional computational fluid dynamics modeling predictions are compared for three different methods of achieving high-efficiency, low NOx, and soot premixed charge compression ignition (PCCI) combustion. The first method is early injection, highly dilute (i.e., low oxygen concentration), diesel fuel PCCI operation. In this method, the oxygen concentration is reduced to extend the ignition delay to allow adequate time for mixing prior to autoignition. The second method is early injection PCCI operation using neat ethanol. In this method, the fuel reactivity is sufficiently low such that PCCI combustion can be achieved without using external dilution. The final method, dual-fuel reactivity controlled compression ignition (RCCI) combustion, blends fuels with different ignition qualities in the combustion chamber to tailor the auto-ignition properties of the mixture for the specific operating condition. In this study, RCCI operation was investigated using in-cylinder fuel blending of diesel fuel and gasoline as well as diesel fuel and an E85 blend (i.e., 85% ethanol and 15% gasoline). It was found that the modeling approach used in this work is capable of capturing the bulk combustion characteristics (e.g., cylinder pressure) as well as the details of the injection event (e.g., liquid penetration) and ignition processes. The simulations were shown to provide accurate predictions of the differences in combustion characteristics of diesel fuel, ethanol, and fuel blends (i.e., gasoline + diesel fuel and E85 + diesel fuel). It was found that the ethanol PCCI and dual-fuel (gasoline + diesel fuel and E85 + diesel fuel) RCCI cases have significantly reduced rates of energy release compared to neat diesel fuel PCCI operation. The reduced energy release rates of the ethanol PCCI and dual-fuel RCCI cases may allow these modes of PCCI combustion to achieve higher engine loads than that of neat diesel PCCI.