Octane Response in a Downsized, Highly Boosted Direct Injection Spark Ignition Engine

Abstract

Increasingly strict government emissions regulations in combination with consumer demand for high performance vehicles is driving gasoline engine development towards highly downsized, boosted direct injection technologies. In these engines, fuel consumption is improved by reducing pumping, friction and heat losses, yet performance is maintained by operating at higher brake mean effective pressure. However, the in-cylinder conditions of these engines continue to diverge from traditional naturally aspirated technologies, and especially from the Cooperative Fuels Research engine used to define the octane rating scales. Engine concepts are thus key platforms with which to screen the influence of fundamental fuel properties on future engine performance.'ULTRABOOST', a collaborative research project which is co-funded by the Technology Strategy Board (TSB), the UK's innovation agency, is a downsized, highly boosted, 2.0L in-line 4 cylinder prototype engine, designed to achieve 35% CO 2 emissions reduction without compromising the performance of a 5.0L V8 naturally aspirated production engine. To probe engine response to fuel, a matrix of 14 formulations was tested at several engine conditions. This is the first in a series of fuel related papers and focuses on the engine's response to the research octane number (RON). The knock limited spark advance was determined for a series of fuels with RON varying from 95 to 112; octane was shown to provide 5 or 10° crank angle advance in knock limited spark advance at 2000 and 3000 rpm, respectively. This study demonstrates that fuel octane quality continues to be important for the performance of emerging downsized engine technologies. Furthermore, the trend for continued engine downsizing will increase the potential performance benefit associated with knock resistant fuels.

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“…The other test results have been reported elsewhere. [36][37][38] The test points used are shown in Table 3. BMEP: brake mean effective pressure; BTDC: before top dead centre.…”

“…The higher exhaust back pressure of test point D was intended to reduce the knock limit of the engine with respect to point C. For more information on the rationale behind choosing these test conditions, see Remmert and colleagues. [36][37][38] As described above at each point, a spark loop was conducted with the relative AFR held at l = 1 (i.e. the stoichiometric AFR) and the boost conditions were held constant (i.e.…”

Ultra Boost for Economy: Extending the Limits of Extreme Engine Downsizing

“…It had thus technically met both the maximum torque and power targets within Phase 2. EBP downstream of the turbine during this test was 33 kPa at maximum power; while this may seem low, from previous work with the CAHU (for example during the fuels test described in [24]) the engine had not displayed any great sensitivity to EBP, although further tests are planned to be conducted in this area with the UB200 build specification. During this phase there was one instance of preignition which was not of the LSPI type.…”

“…The use of the CAHU and EGR rig permitted very tightly controlled boosting conditions, and were found to be ideal for such tests. The results of the specific fuel experiments will be reported elsewhere [24].…”

“…These are reported elsewhere [23,24]. For most of the Phase 2 testing, after the base performance of the combustion system had been ascertained, the engine was run to help validate the 1-D model and to demonstrate that, after the supercharger drive torque had been taken into account, the target performance would be achievable with the UB200 build and its self-driven charging system.…”