Experimental Evaluation of a Custom Gasoline-Like Blend Designed to Simultaneously Improve ϕ-Sensitivity, RON and Octane Sensitivity

ϕ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. However, regular gasoline is not very ϕ-sensitive at low-pressure conditions, meaning that intake boosting (typically P_in ≥ 1.3 bar) is required to take advantage of this property. Thus, there is strong motivation to design a gasoline-like fuel that simultaneously improves ϕ-sensitivity, RON and octane sensitivity, to make an improved fuel suitable for both LTGC and modern SI engines. In a previous study [SAE 2019-01-0961], a 5-component regulation-compliant fuel blend (CB#1) was computationally designed; and simulations showed promising results when it was compared to a regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in the Sandia LTGC engine and compares the results with those of RD5-87. The RON and octane sensitivity were improved 1.3 and 3.6 units by CB#1, respectively. Similar amounts of intake heat are required to achieve autoignition of CB#1 and RD5-87 at premixed, naturally aspirated conditions, ensuring that CB#1 can operate under HCCI mode as easily as regular gasoline. Furthermore, similar maximum engine loads can be reached with both CB#1 and RD5-87 under premixed, high-boost conditions. The ϕ-sensitivity was evaluated using two metrics. First, starting from well-mixed conditions, the change in CA10 with a specific amount of fuel stratification provides a metric of how the ϕ-sensitivity advances the ignition. Second, the amount of CA50 advancement without knock that is achievable with stratification provides a metric of how the ϕ-sensitivity spreads the heat release. Both metrics showed that CB#1 has a greater ϕ-sensitivity than RD5-87. Additionally, CB#1 has a lower peak heat release rate than RD5-87 for stratified operation with the same combustion phasing because of the larger spread of heat release, leading to lower combustion noise and lower knock propensity. Finally, CB#1 was found to be a more suitable fuel to work with ignition enhancers, such as EHN, compared to RD5-87.