Combustion Performance of Hydrogen Direct Injection under Lean-burn Conditions for Power Generation

This paper studies the combustion phenomenon of hydrogen (H2) direct injection (DI) in a modified spark ignition (SI) engine. As we known, ignition timing strongly correlates with combustion performance, especially for power output and efficiency. Therefore, different ignition timing varying among -20, -15, -10, -5, 0, 5, 10, 15, and 20 deg top dead center (TDC) are tested in this research. Besides, different H2 injection timings and injection pressures are also compared in this study. Moreover, as H2 usually favors lean-burn combustion, λ at 3, 3.5, and 4 are tested to find the lean-burn limitation. In order to obtain the engine speed influences on power output, finally 1500, 2000, and 2500 revolutions per minute (rpm) are evaluated in this study. Finally, thermal brake efficiency (BTE) and power output are analyzed. Results showed that power output and efficiency increase with the delay of ignition timing from -20 to 5 deg TDC and then decrease with delaying timing from 5 to 20 deg TDC. However, injection timing has less effect on the H2 combustion phenomenon. H2 lean-burn limitation is found that when λ is larger than 3, the efficiency decreases sharply. Moreover, both power output and efficiency firstly increase then decrease with higher engine speed and 2000 rpm is the best option for this small engine. Finally, by evaluating the contribution index, ignition timing and engine speed should be optimized first to achieve higher efficiency

Large eddy simulation of fuel-air mixing process in a convergent-divergent duct spray under non-vaporizing conditions

The spray mixing process can be improved via straight (ST) duct fuel injection, but there is a risk of potential heat transfer loss due to prolonged spray tip penetration (STP) and spray impingement. We proposed a convergent-divergent (CD) duct spray to produce an acceptable STP along with improved spray air entrainment and spray cone angle (SCA), which is validated in optical spray experiments. How the CD duct enhances the fuel–air mixing and why the spray left–right swing phenomenon occurs near the outlet of the CD duct is still unknown. This study focuses on the spray mixing process inside CD and ST ducts using large eddy simulations. Results showed that the larger vortex cluster is formed in the divergent outlet with the large diameter of 4.5 mm and 6 mm, named CD4.5 and CD6 ducts, which leads to the unstable fluctuations of the separated shear flow and a large number of vortex shedding from the inner wall of the CD duct outlet to promote the radial fuel–air mixing with the left–right swing phenomenon, which further enlarges the SCA and appropriately shortens the STP with reduced spray energy. Compare to free spray, there are two turbulence kinetic energy (TKE) peaks in the spray axial centerline, indicating that duct spray brings extra disturbance to spray and is conducive to promoting the fuel–air mixing process. The strongest TKE region appears near the outlet of CD4.5 and CD6 duct sprays that are consistent with the left–right spray swing motion phenomenon

Study on fermentation gas combustion with hydrogen addition under various throttle openings

Regional energy systems are designed to contribute to a green and “carbon neutral” economy of localities. In this system, the engine combustion is significant for power generation. Therefore, this study mainly investigated the effect of throttle openings on the combustion characteristics of hydrogen (H2) and methane (CH4) mixtures to achieve high efficiency. Throttle opening has a strong relationship with combustion performance, particularly for power output and efficiency. Therefore, 10%, 20%, 40%, and 100% throttle openings were tested to obtain higher efficiency for power generation. Combustion characteristics of CH4 and CH4+H2 were also compared. With H2 addition, the volume percentage of H2 varied between 10%, 30%, and 50%. The ratio of air to gas fuel was controlled to determine λ varying from 1.0 to 1.4. Subsequently, the effect of throttle openings under different λ with H2 addition was examined. Finally, brake thermal efficiency (BTE), power output, brake mean effective pressure (BMEP) and brake specific fuel consumption (BSFC) were compared. Moreover, the maximum value of the cylinder pressure in cycles (Pmax) and the coefficient of variation (COV) in Pmax were discussed. The results showed that the torque and power output decreased slightly from full throttle opening to 40% throttle opening. The 30% H2 addition in Case # 5 (full opening under lean-burn conditions) is the best working condition to satisfy both the power generation and energy-saving requirements in this study. Furthermore, Pmax decreased with smaller throttle opening, and H2 addition increased Pmax. In addition, H2 addition decreased COV, but throttle opening had less effect on COV

Development of a chemical kinetic mechanism for ammonia/macromolecular hydrocarbon combustion

C-free fuel ammonia has a high auto-ignition temperature and low flame speed compared to conventional hydrocarbon fuels, which limits its application in internal combustion engines (ICEs). Blending ammonia (NH3) with a highly reactive fuel can effectively solve this problem, and traditional macromolecular hydrocarbon fuels are a good choice because of their practicality and economy. However, the chemical reaction mechanism for the combustion of NH3/macromolecular hydrocarbons is not yet fully understood. In this study, a detailed kinetic mechanism for NH3 and toluene reference fuel (TRF) is proposed with 250 species and 4272 reactions. The developed NH3/TRF mechanism was validated by a single component (NH3, n-heptane, iso-octane, and toluene) and multiple components (NH3/n-heptane, NH3/iso-octane, NH3/toluene) with ignition delay time, laminar burning velocity, and key intermediate component distribution. The current NH3/TRF mechanism showed good performance compared with previous mechanisms. The co-combustion of NH3/TRF blends was performed with different NH3 energy fractions, and sensitivity and reaction pathway analyses were performed to reveal the effect of TRF addition on NH3 combustion. The results showed that the OH radical is mainly produced through N-containing reactions rather than C-containing reactions under T = 1000 K, P = 40 atm, and ϕ = 1 with more than 30 % NH3 addition. The HO2 radical is the most important radical for NH3 ignition, in addition to OH radicals, and its reactions with N-containing radicals (NH2, H2NO, and NO) contribute to the majority of OH radicals

In-Cylinder Combustion and Soot Evolution in the Transition from Conventional Compression Ignition (CI) Mode to Partially Premixed Combustion (PPC) Mode

The present study intends to explore the in-cylinder combustion and evolution of soot emission during the transition from conventional compression ignition (CI) combustion to partially premixed combustion (PPC) under low load conditions. In-cylinder combustion images and engine-out emissions were measured in an optical engine fueled with low octane heavy naphtha fuel (RON = 50). Full cycle engine simulations were performed using a three-dimensional computational fluid dynamics code CONVERGE, coupled with gas-phase chemical kinetics, turbulence, and a particulate size mimic soot model. The simulations were performed under low load conditions (indicated mean effective pressure (IMEP) of ∼2–3 bar) at an engine speed of 1200 rpm. The start of injection (SOI) was advanced from late (−10 CAD aTDC) to early fuel injection timings (−40 CAD aTDC) to realize the combustion transition from CI combustion to PPC. The simulation results of combustion and emission are compared with the experimental results in both CI and PPC combustion modes. The results of the study show a typical low-temperature stratified lean combustion in PPC mode, while high-temperature spray-driven combustion is evident in CI mode. The in-cylinder small intermediates species such as acetylene (C₂H₂), propargyl (C₃H₃), cyclopentadienyl (C₅H₅), and polycyclic aromatic hydrocarbons (PAHs) were significantly suppressed at PPC mode. Nucleation reaction of PAHs collision contributed to main soot mass production. The distribution of soot mass and particle number density was consistent with the distribution of high-temperature zones in CI and PPC combustion modes

A recurrence‐predictive model based on eight genes and tumor mutational burden/microsatellite instability status in Stage II/III colorectal cancer

Abstract Background Although adjuvant chemotherapy (ACT) is widely used to treat patients with Stage II/III colorectal cancer (CRC), administering ACT to specific patients remains a challenge. The decision to ACT requires an accurate assessment of recurrence risk and absolute treatment benefit. However, the traditional TNM staging system does not accurately assess a patient's individual risk of recurrence. Methods To identify recurrence risk‐related genetic factors for Stage II/III CRC patients after radical surgery, we conducted an analysis of whole‐exome sequencing of 47 patients with Stage II/III CRC who underwent radical surgery at five institutions. Patients were grouped into non‐recurrence group (NR, n = 24, recurrence‐free survival [RFS] > 5 years) and recurrence group (R, n = 23, RFS <2 years). The TCGA‐COAD/READ cohort was employed as the validation dataset. Results A recurrence‐predictive model (G8plus score) based on eight gene (CUL9, PCDHA12, HECTD3, DCX, SMARCA2, FAM193A, AATK, and SORCS2) mutations and tumor mutation burden/microsatellite instability (TMB/MSI) status was constructed, with 97.87% accuracy in our data and 100% negative predictive value in the TCGA‐COAD/READ cohort. For the TCGA‐COAD/READ cohort, the G8plus‐high group had better RFS (HR = 0.22, p = 0.024); the G8plus‐high tumors had significantly more infiltrated immune cell types, higher tertiary lymphoid structure signature scores, and higher immunological signature scores. The G8plus score was also a predict biomarker for immunotherapeutic in advanced CRC in the PUCH cohort. Conclusions In conclusion, the G8plus score is a powerful biomarker for predicting the risk of recurrence in patients with stage II/III CRC. It can be used to stratify patients who benefit from ACT and immunotherapy