Development and validation of an EHN mechanism for fundamental and applied chemistry studies
2022-01-0546
03/29/2022
- Event
- Content
- Autoignition enhancing additives have been used for years to enhance the ignition quality of diesel fuel, with 2-ethylexyl nitrate (EHN) being the most common additive. EHN also enhances the autoignition reactivity of gasoline, which has advantages for some low-temperature combustion techniques, such as Sandia’s Low-Temperature Gasoline Combustion (LTGC) with Additive-Mixing Fuel Injection (AMFI). LTGC-AMFI is a new high-efficiency and low-emissions engine combustion process based on supplying a small, variable amount of EHN into the fuel for better engine operation and control. However, the mechanism by which EHN interacts with the fuel remains unclear. In this work, a chemical-kinetic mechanism for EHN was developed and implemented in a detailed mechanism for gasoline fuels. The combined mechanism was validated against shock-tube experiments with EHN-doped n-heptane and HCCI engine data for EHN-doped regular E10 gasoline. Simulations showed a very good match with experiments. EHN chemistry fundamentals were also studied. Under LTGC-AMFI engine conditions, EHN generates NO2, formaldehyde and a combination of ~85% 3-heptyl and ~15% 1-butyl and 1-propyl radicals. Results show that the 3-heptyl and 1-butyl radicals are responsible for the autoignition-enhancing effect of EHN. Each mole of these radicals rapidly generates 2 moles of OH, which accelerate the low-temperature chemistry of the fuel, increasing its reactivity. The effects of the operating conditions on the effectiveness of EHN were also studied. EHN’s effectiveness is highest in the low-temperature regime, and it decreases as the temperature increases. EHN’s effectiveness decreases with intake-pressure boost and with EGR for typical engine operation. The effect of EHN increases as the equivalence ratio increases, which enhances the fuel’s φ-sensitivity. Therefore, with fuel stratification, EHN’s larger effect on richer regions causes a greater autoignition advancement and a greater spread of heat release compared to the same stratification without EHN. Thus, stratification techniques are more effective with EHN addition.
- Citation
- Lopez Pintor, D., and Dec, J., "Development and validation of an EHN mechanism for fundamental and applied chemistry studies," SAE Technical Paper 2022-01-0546, 2022, .