Experimental Study of Fuel Composition Impact on PCCI Combustion in a Heavy-Duty Diesel Engine

Abstract

Premixed Charge Compression Ignition (PCCI) is a combustion concept that holds the promise of combining emission levels of a spark-ignition engine with the efficiency of a compression-ignition engine. In a short term scenario, PCCI would be used in the lower load operating range only, combined with conventional diesel combustion at higher loads. This scenario relies on using near standard components and conventional fuels; therefore a set of fuels is selected that only reflects short term changes in diesel fuel composition.Experiments have been conducted in one dedicated test cylinder of a modified 6-cylinder 12.6 liter heavy duty DAF engine. This test cylinder is equipped with a stand-alone fuel injection system, EGR circuit and air compressor. For the low load operating range the compression ratio has been lowered to 12:1 by means of a thicker head gasket. It is shown that emission levels and performance strongly correlate with the combustion delay (CD=CA50-SOI), independent of how this combustion delay is achieved.In a longer term scenario, both engine hardware and fuels can be adapted to overcome intrinsic PCCI challenges. At higher loads and at 15:1 compression ratio, necessary for good full load efficiency, a less reactive fuel is required to delay auto-ignition and phase combustion correctly. A number of low reactivity fuel blends have been used to investigate the desired Cetane Number for PCCI operation at different loads. For these blends too, all emission levels as well as the efficiency are shown to greatly correlate with the combustion delay. With an improved efficiency because of the higher compression ratio, the blend with an estimated CN of 25 was found to be the most flexible in being able to choose the optimum CD for the conditions and load used.

The Nature of Heat Release in Gasoline PPCI Engines

“…Then a second late injection close to TDC would provide the charge stratification to control the heat release rate [1]. As such, the combustion phenomena studied here are different from the PPCI work using diesel fuel [5,6], for which the vaporization and ignition delays are very different; from using single injection [7], for which the emphasis is not on putting a pilot fuel over a background nearly homogeneous charge; and from using dual fuels such as the reactivity controlled compression ignition (RCCI) concept [8][9][10], for which the reactivity of the local charge is controlled by using two fuels of different reactivity.…”

Pre- and post-injection flow characterization in a heavy-duty diesel engine using high-speed PIV

“…Premixing occurs in the ignition delay (ID) period, which is defined as the time between start of injection (SOI) and the start of combustion (SOC). When a diesel engine is operated in PCCI mode, the ignition delay is (much) larger as compared to conventional diesel combustion and larger than ten crank angle degrees (CAD) as shown by Leermakers et al (2011). Currently, injection pressures in heavy-duty diesel engines of up to 2,500 bar, combined with a long ignition delay, improve the mixing of fuel and air prior to combustion.…”

Commercial Naphtha Blends for Partially Premixed Combustion

“…For more information on the setup the reader is referred to a detailed description [8], of which this subsection is a short summary. Prior to this measurement campaign, the engine has been overhauled with new pistons and liners.…”

“…Conventional fuels, i.e. diesel [8] or gasoline [9] imply a number of challenges for this concept, but fuels in the gasoline boiling range, with relative lowoctane-number were shown to be very well suitable for this concept [10]. The load range over which the concept can be applied was shown to depend on the reactivity.…”