Effect of engine conditions and injection timing on piston-top fuel films for stratified direct-injection spark-ignition operation using E30

Self Cite

Lean operation of Spark-Ignition engines can provide higher thermal efficiency compared to standard stoichiometric operation. However, for a homogeneous lean mixture, the associated reduction of flame speeds becomes an important issue from the perspective of robust ignition and fast flame spread throughout the charge. This study is focused on the use of a lean partial fuel stratification strategy that can stabilize the deflagration, while sufficiently fast combustion is ensured via the use of end-gas autoignition. The engine has a spray-guided Direct-Injection Spark-Ignition combustion system and was fueled with either a high-octane certification gasoline or E85. Partial fuel stratification was achieved using several fuel injections during the intake stroke in combination with a small pilot-injection concurrent with the Spark-Ignition. The results reveal that partial fuel stratification enables very stable combustion, offering higher thermal efficiency for parts of the load range in comparison to well-mixed lean and stoichiometric combustion. The heat release and flame imaging demonstrate that the combustion often has three distinct stages. The combustion of the pilot-injected fuel, ignited by the normal spark, acts as a “super igniter,” ensuring a very repeatable initiation of combustion, and flame incandescence reveals locally rich conditions. The second stage is mainly composed of blue flame propagation in a well-mixed lean mixture. The third stage is the compression autoignition of a well-mixed and typically very lean end-gas. The end-gas autoignition is critical for achieving high combustion efficiency, high thermal efficiency, and stable combustion. Partial fuel stratification enables very effective combustion-phasing control, which is critical for controlling the occurrence and intensity of end-gas autoignition. Comparing the gasoline and E85 fuels, it is noted that achieving end-gas autoignition for the higher octane E85 requires a more aggressive compression of the end-gas via the use of a more advanced combustion phasing or higher intake-air temperature.

Section: Resultsmentioning

confidence: 99%

The use of partial fuel stratification to enable stable ultra-lean deflagration-based Spark-Ignition engine operation with controlled end-gas autoignition of gasoline and E85

Zhang

Sjöberg

et al. 2019

Self Cite

“…To visualize and measure the formation and evaporation of the fuel films on the piston crown, they developed a high-speed imaging technique based on refractive-index-matching (RIM). 30 This technique, which exploits the change in light scattering (reflection 4,9,12 or transmission 3 ) from a rough surface when it is wetted by a liquid, has also been used in three papers in this special issue. 3,4,9 Results under warmed-up, part-load stratified conditions showed that—in contrast to some earlier expectations—the fuel-film mass correlated quantitatively with engine-out soot mass, whereas the amount of fuel on the piston was small (typically ∼0.1−1%) and did not contribute significantly to HC emissions.…”

Section: Swis—challenges and Developmentsmentioning

confidence: 99%

“…Only one paper in this collection presents experiments that were performed in an engine. Ding et al 4 investigate spray impingement and wall wetting with E30 fuel (30% ethanol, 70% gasoline) in the increasingly common central-injection GDI configuration. Here, the engine operated in spray-guided stratified-charge mode with late injection.…”

Section: Papers In This Special Issuementioning

confidence: 99%

“…This special issue of International Journal of Engine Research (IJER) presents 11 papers that investigate spray-wall interactions (SWIs) and their effects at both fundamental and practical levels. These studies include numerical simulations 1–3 and measurements 4–8 of SWIs and fuel-film formation and dynamics, as well as measurements of fuel-film combustion and emissions processes. 9–11…”

mentioning

confidence: 99%

See 1 more Smart Citation

Spray-wall interactions in direct-injection engines: An introductory overview

Fansler

Trujillo

Curtis

2020

Spray-wall interactions directly affect fuel-air mixture preparation and emissions formation. They are therefore among the most critical physical processes in engines today. This special issue of International Journal of Engine Research presents 11 papers that investigate spray-wall interactions and their effects at both fundamental and practical levels. This brief article offers background and context for the special issue and summarizes each research paper in the collection.

“…Under these conditions, NO x and soot emissions are higher. 3,4 Although after-treatment strategies are effective in reducing exhaust emissions, it would be better to reduce pollutant formation at the source itself. 5,6 Furthermore, a three-way catalytic converter is not an effective strategy for GDI engine since the engine operates at a wide range of equivalence ratios.…”

Section: Introductionmentioning

confidence: 99%

Effects of direct water injection and injector configurations on performance and emission characteristics of a gasoline direct injection engine: A computational fluid dynamics analysis

Raut

Mallikarjuna

2019

In-cylinder water injection is a promising approach for reducing NOx and soot emissions from internal combustion engines. It allows one to use a higher compression ratio by reducing engine knock; hence, higher fuel economy and power output can be achieved. However, water injection can also affect engine combustion and emission characteristics if water injection and injector parameters are not properly set. Majority of the previous studies on the water injection are done through experiments. Therefore, subtle aspects of water injection such as in-cylinder interaction of water sprays, spatial distribution of water vapor, and effect on flame propagation are not clearly understood and rarely reported in literature due to experimental limitations. Thus, in the present article, a computational fluid dynamics investigation is carried out to analyze the effects of direct water injection under various injector configurations on water evaporation, combustion, performance, and emission characteristics of a gasoline direct injection engine. The emphasis is given to analyze in-cylinder water spray interactions, flame propagation, water spray droplet size distribution, and water vapor spatial distribution inside the engine cylinder. For the study, the water-to-fuel ratio is varied from 0 to 1. Various water injector configurations using nozzle hole diameters of 0.14, 0.179, and 0.205 mm, along with nozzle holes of 4, 5, 6, and 7, are considered for comparison in addition to the case of no_water. Computational fluid dynamics models used in this study are validated with the available data in literature. From the results, it is found that the emission and performance characteristics of the engine are highly dependent on water evaporation characteristics. Also, the water-to-fuel ratio of 0.6 with 6 number of nozzle holes and the nozzle diameter of 0.14 mm results in the highest indicated mean effective pressure and the lowest NOx, soot, and CO emissions compared to other cases considered.