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Experimental evaluation of a custom gasoline-like blend designed to simultaneously improve φ-sensitivity, RON and octane sensitivity.
ISSN: 0148-7191, e-ISSN: 2688-3627
To be published on April 14, 2020 by SAE International in United States
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 only weakly φ–sensitive at naturally aspirated conditions, so intake boosting is required to take advantage of this property. Thus, there is strong motivation for designing gasoline-like blends that improve φ–sensitivity and simultaneously increase RON and octane sensitivity, to improve performance for 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 compared to regular E10 gasoline (RD5-87). The current study experimentally evaluates CB#1 in a LTGC research engine, and the results are compared to RD5-87. For premixed naturally aspirated conditions, the intake heating required to autoignite CB#1 was similar to RD5-87, ensuring that CB#1 can operate under these conditions as easily as regular gasoline. Furthermore, similar maximum engine loads were reached with both CB#1 and RD5-87 under premixed, high-boost conditions. An independent analysis showed that the RON and octane sensitivity were increased 1.3 and 3.6 units, respectively, with CB#1. The φ–sensitivity at naturally aspirated conditions was evaluated using two metrics. First, starting from well-mixed conditions, the change in CA10 for a given amount of stratification provides a metric of how the φ–sensitivity advances ignition. Second, the extent to which stratification can advance CA50 without engine knock provides a measure of how much the φ–sensitivity spreads the heat release. Results showed that both metrics were improved using CB#1 compared to RD5-87, confirming that CB#1 is more φ–sensitive than RD5-87. Additionally, CB#1 was found to give a lower peak of heat release rate than RD5-87 for the same combustion phasing due to its longer burn duration, leading to lower noise, lower heat losses and higher thermal efficiencies.