Alternative Fuel Mixing Controlled Compression Ignition
Motivation:
Improve understanding of high-speed direct-injection (HSDI) operating strategies and the tradeoffs between improved efficiency/emissions and disadvantages that limit market acceptance, such as combustion instability and load limitations. The project is focused on the use of low-cetane fuels, specifically market gasoline or bio-gasoline, in compression ignition (CI) engines, while achieving mixing-controlled combustion. These strategies allow for the use of ignition control methods that are familiar to users of diesel-fueled CI engines while offering the emissions and GHG benefits of low-cetane fuels.
Tasks:
- Study the use of an offset active prechamber (OAP) for low load ignition assistance.
- Development of a new methodology, the ignition assistance number (IAN), to quantify the improvement of different ignition assistance techniques under mixing controlled compression ignition operation.
Key Findings:
- The offset active prechamber significantly improves combustion stability under low load operation (3 bar IMEP) with gasoline compression ignition (GCI).
Application:
- The prechamber enabled mixing-controlled combustion (PCMCC) strategy is a promising approach to use low cetane fuels in a mixing controlled combustion mode.
- This technique is a potential pathway towards a flex-fuel, MCCI technology.
Figure 1. Left – CAD Model of the Prechamber setup next to the DI Fuel Injector. Red and blue plumes show the interaction between the prechamber jets and main injector jets. Right – Installed prechamber with a combination spark plug and pressure transducer (the blue wire).
Hydrogen Internal Combustion Engine – Modeling
Motivation:
Investigate details of direct-injection spark-ignited H2 combustion through a combined modeling / experimental study with the goal of improved performance and emissions capability over the full range of engine loads.
Tasks:
- Assess and develop engineering level computational fluid dynamics (CFD) modeling approaches for high pressure hydrogen injection and combustion
- Validate CFD model predictions through comparisons with engine experimental data acquired in complementary experimental project and support experimental effort to improve understanding of hydrogen combustion
- Apply CFD models to provide insight into approaches to utilize hydrogen in direct injection engines
Program Goals:
- Provide insight into approaches and model needs for engineering-level H2 engine simulations
- Provide precompetitive assessment of methods to improve H2 combustion performance
Application:
- Direct-injection spark-ignited engines running on pure H2 and blends of H2 + NG
Figure 1. Hydrogen Injection Model Development showing a comparison of the Inflow model (detailed, Lagrangian) and the Parcel model (simplified, Eulerian) with experimental results.
Ethanol Direct Injection Compression Ignition
Motivation:
Development of robust and practical approaches to assist the ignition of ethanol and ethanol blends (Cetane number ~10) in direct injection compression ignition engines to enable mixing-controlled combustion under low-load conditions. These approaches will seek to improve the stability of ethanol combustion and reduce low-load CO, soot, and UHC emissions. The proposed methods to be investigated include e-Boosting (intake pressure boosting via electric supercharger), intake heating, and in- cylinder residual gas trapping. The project will develop system-level approaches through 1-D modeling and experimentation to ensure robust combustion despite the low ignitability and high heat of vaporization of ethanol. Results will inform strategies for other low GHG renewable fuels such as methanol, bio-naphtha, and renewable gasoline.
Tasks:
- Develop map of ignition delay for base diesel fuel and E85 over a range of in-cylinder thermodynamic conditions at start of injection
- Identify and develop approaches to achieve the needed in-cylinder thermodynamic conditions to sustain mixing-controlled ethanol combustion
- Study approaches using 1-D systems level modeling
- Modify hardware (as needed) and experimentally validate promising solutions
Program Goals:
- Devise simple / practical hardware approaches to achieve desired robust light-load ignition characteristics
- Improve combustion stability, reduce CO and UHC for low load operation
Application:
- Direct-injection engines using ethanol, ethanol-gasoline blends and other low cetane (high octane) fuels
Figure 1. Schematic illustration of project
Physics of Fuel Injection and Spray Breakup
Motivation:
Fuel atomization and spray formation processes have long been among the most challenging areas to investigate due to the short time and length scales present and the overwhelming density of droplets in the near-nozzle region. These processes set the initial conditions for air entrainment, mixing, and subsequent ignition. This project aims to employ high-fidelity computational tools, modern data science techniques, and the latest fluid mechanics analysis methods to study fuel atomization and spray formation. This is particularly relevant these days as new fuels with vastly different physical properties compared to conventional fuels are being considered.
Tasks:
- Develop mathematical framework for spray breakup with particular emphasis on alternative fuels having zero to low-carbon content, particularly, methanol.
- Improve numerical techniques for simulating atomization.
- Continue the construction of physics-based framework for the development of new spray models.
Key Findings:
- Contrary to the conventional understanding of spray formation, it is the large-scale perturbations that are responsible for much of the liquid breakup.
- Well-established ideas of self-similarity developed for gas jets have proven to be present in surprising ways in fuel sprays.
Application:
- Improved spray modeling and control strategies for direct injection engines employing conventional and new low-carbon liquid fuels.
Figure 1. Illustration of primary jet regimes.
Figure 2. Hybrid Eulerian – Lagrangian Volume of Fluid (VoF) Simulations
