Effect of cold start on engine performance and emissions from diesel engines using IMO-Compliant distillate fuels

Impact of fuel aromatic content on soot particle physicochemical properties of marine auxiliary diesel engine

Fuel aromatic content (AC) is one of the main reasons for PM (particulate matter) emissions from ocean-going ships. The present study investigates the influence of AC on physicochemical characteristics of soot particles from marine auxiliary diesel engine. The TEM (transmission electron microscopy), Raman spectroscopy, FTIR (Fourier transform infrared spectroscopy), and TGA (thermalgravimetric analyzer) are employed to jointly characterize samples. The results reveal that soot particles from high-AC fuel have bigger d_p (primary particle size), longer fringe length (La), and higher graphitization degree, all of which have significant impacts on chemical properties such as more VOF (volatile organic fraction), higher concentrations of aromatic C-H and C=C groups. These are mainly due to several aromatic rings decomposed from aromatic components could promote the growth of carbon layer, and incomplete pyrolysis productions are also present in soot particles. The relative amounts of aromatic C-H and C=C are well correlated with d_p and La, respectively.

Emission Characteristics and Formation Pathways of Intermediate Volatile Organic Compounds from Ocean-Going Vessels: Comparison of Engine Conditions and Fuel Types

The lack of emission data for ocean-going vessels (OGVs) and the recent fuel switching make it urgent to enhance the onboard measurement of ship emissions, especially for intermediate volatile organic compounds (IVOCs). This study focused on the IVOC emission characteristics and formation pathways of three OGVs under various engine conditions (power and load) and fuel oils (heavy fuel oil (HFO) versus marine gas oil (MGO)). The results showed that the (1) IVOC emission factors (EF_IVOC) of the three OGVs increased with engine power and were higher for MGO (1494.4 ± 421.7 mg/kg) than HFO (1830.5 ± 534.5 mg/kg) and engine load is an important parameter. (2) Engine load and oil type affect the composition and volatility distribution of IVOCs. The proportion of polycyclic aromatic hydrocarbons in IVOCs increased with a higher load, and using MGO shifted IVOC components to a higher volatility in contrast to HFO. (3) The compositions of IVOCs were more like those in fuel oils under low loads than under high loads, indicating that different formation pathways of IVOCs exist for different engine loads. (4) A higher EF_IVOC was observed nearshore than in open sea owing to the lower and transient engine load, which indicates the necessity of paying attention to the IVOC emissions for ships.

An overview of the deactivation mechanism and modification methods of the SCR catalysts for denitration from marine engine exhaust

Selective catalytic reduction (SCR) technology is currently the most effective deNO_x technology and has broad application prospects. Moreover, there is a large NO_x content in marine engine exhaust. However, the marine engine SCR catalyst will be affected by heavy metals, SO₂, H₂O_(g), hydrocarbons (HC) and particulate matter (PM) in the exhaust, which will hinder the removal of NO_x via SCR. Furthermore, due to the high loading operation of the marine engine and the regeneration of the diesel particulate filter (DPF), the exhaust temperature of the engine may exceed 600 °C, which leads to sintering of the SCR catalysts. Therefore, the development of new catalysts with good tolerances to the above emissions and process parameters is of great significance for further reducing NO_x from marine engines. In this work, we first elaborate on the mechanism of the SCR catalyst poisoning caused by marine engine emissions, as well as the working mechanism of SCR catalysts affected by the engine exhaust temperature. Second, we also summarize the current technologies for improving the properties of SCR catalysts with the aim of enhancing the resistance and stability under complex working conditions. Finally, the challenges and perspectives associated with the performance optimization and technology popularization of marine SCR systems are discussed and proposed further. Consequently, this review may provide a valuable reference and inspiration for the development of catalysts and improvement in the denitration ability of SCR systems matched with marine engines.

Effect of the Preheating Strategy on the Combustion Process of the Intake Manifold Burner

The intake air preheating is an effective method to improve the cold start performance of diesel engines. The combustion process and ignition probability were investigated in the present study. The average flame area (AFA) during the steady stage of the combustion process was used to evaluate the effects of various factors on combustion. The increase of voltage was found to enhance the combustion process, while the increased diesel flow rate first promoted the combustion before deteriorating it. The increased intake air flow velocity enhanced the combustion within 2.64 m/s, and excessive air flow velocity hindered the combustion from 2.7 to 3 m/s. The cross-distributed vortex clusters in the combustion chamber, periodic diesel evaporation and vortexes with opposite rotation directions in the vicinity of the intake manifold burner were believed to be the main reasons for flame stripping and swirl motion. The temperature rise in the exhaust pipe was recorded to investigate the thermal distribution. The warm air was concentrated in the upper region because of the buoyancy effect of the flame. With the air flow velocity increasing from 1.4 to 10 m/s, the average temperature rise increased first before decreasing, while the combustion efficiency increased due to the increased air flow volume.

Analysis of cold-start NO2 and NOx emissions, and the NO2/NOx ratio in a diesel engine powered with different diesel-biodiesel blends

In the transportation sector, the share of biofuels such as biodiesel is increasing and it is known that such fuels significantly affect NOx emissions. In addition to NOx emission from diesel engines, which is a significant challenge to vehicle manufacturers in the most recent emissions regulation (Euro 6.2), this study investigates NO₂ which is a toxic emission that is currently unregulated but is a focus to be regulated in the next regulation (Euro 7). This manuscript studies how the increasing share of biofuels affects the NO₂, NOx, and NO₂/NOx ratio during cold-start (in which the after-treatment systems are not well-effective and mostly happens in urban areas). Using a turbocharged cummins diesel engine (with common-rail system) fueled with diesel and biofuel derived from coconut (10 and 20% blending ratio), this study divides the engine warm-up period into 7 stages and investigates official cold- and hot-operation periods in addition to some intermediate stages that are not defined as cold in the regulation and also cannot be considered as hot-operation. Engine coolant, lubricating oil and exhaust temperatures, injection timing, cylinder pressure, and rate of heat release data were used to explain the observed trends. Results showed that cold-operation NOx, NO₂, and NO₂/NOx ratio were 31-60%, 1.14-2.42 times, and 3-8% higher than the hot-operation, respectively. In most stages, NO₂ and the NO₂/NOx ratio with diesel had the lowest value and they increased with an increase of biofuel in the blend. An injection strategy change significantly shifted the in-cylinder pressure and heat release diagrams, aligned with the sudden NOx drop during the engine warm-up. The adverse effect of cold-operation on NOx emissions increased with increasing biofuel share.

Gaseous Emissions from a Seagoing Ship under Different Operating Conditions in the Coastal Region of China

Pollution caused by ship emissions has drawn attention from various countries. Because of the high density of ships in ports, channels, and anchorages and their proximity to the densely populated areas, ship emissions will considerably impact these areas. Herein, a Chinese seagoing ship is selected and a platform is established for monitoring the ship emissions to obtain detailed characteristics of the ship’s nearshore emissions. The ship navigation and pollution emission data are obtained under six complete operating conditions, i.e., berthing, manoeuvring in port, acceleration in a channel, cruising, deceleration before anchoring, and anchoring. This study analyzes the concentrations of the main emission gases (O2, NOX, SO2, CO2, and CO) and the average emission factors (EFs) of the pollution gases (NOX, SO2, CO2, and CO) based on the engine power under different operating conditions. Results show that the change in O2 concentration reflects the load associated with the main engine of the ship. The NOX, SO2, and CO2 emission concentrations are the highest during cruising, whereas the peak CO emission concentration is observed during anchoring. The average EFs of NOX and SO2 based on the power of the main engine are the highest during cruising, and those of CO2 and CO are the highest after anchoring. The ship EFs are different during acceleration and deceleration. By comparing the EFs along the coast of China and the global EFs commonly used to perform the emission inventory calculations in China, the NOX EFs under different operating conditions is observed to be generally lower than the global EFs under the corresponding operating conditions. Furthermore, the SO2 EF is considerably affected by the sulfur content in the fuel oil and the operating conditions of the ship. The average CO2 EFs are higher than the global EFs commonly used during cruising, and the CO EFs are higher than the global EFs under all the conditions. Our results help to supplement the EFs for this type of ship under different operating conditions, resolve the lack of emission data under anchoring conditions, and provide data support to conduct nearshore environmental monitoring and assessment.