**3.2 Premixed charge compression ignition (PCCI)**

Too early injection of fuel with a higher injection pressure can result in premixed charge compression ignition. Due to early fuel injection, the time between commencement of injection and start of combustion has been extended, considerably

#### *Zero Emission Hydrogen Fuelled Fuel Cell Vehicle and Advanced Strategy on Internal… DOI: http://dx.doi.org/10.5772/intechopen.102057*

improving the homogeneity of the air-fuel mixture prior to combustion [41]. With a slightly higher intake charge temperature maintained at 170°C, the PCCI engine may operate from a minimal air-fuel ratio of 34:1 to an excessively lean air-fuel ratio of 80:1 [46]. In comparison to a standard SI engine, the PCCI combustion strategy uses lean-burn technology and operates on a higher compression ratio engine. After all of the fuel had been injected, the PCCI began to burn. Also, unlike traditional combustion, the combustion events are primarily identified by chemical kinetics and do not follow the diffusion mixed combustion and speed of burning. As a result, the injection pattern and fuel combustion do not overlap, reducing the odds of direct combustion control [47]. To achieve the premixed charge in the PCCI combustion, a single stage fuel injection pattern with an earlier start of injection was adopted. However, starting the injection too early causes wall impingement and wall wetness, resulting in incomplete combustion and higher HC and CO emissions. The fuel injection pattern has been adjusted with a split and multiple injection method to alleviate these issues. Despite the fact that the period of the many injections is completed before combustion begins. Controlling auto ignition by early injection is also a critical job in PCCI combustion. To manage the auto ignition and lengthen the ignition delay interval, a higher amount of EGR is used. EGR also aids in lowering in-cylinder temperature and NOx generation due to the dilution of a fresh charge mixture [48].

PCCI combustion has performed better than HCCI combustion due to the stability of the combustion by partially premixed charge and controlled auto ignition rage and temperature. The phasing of combustion in the PCCI is mostly determined by chemical kinetics, but it can also be influenced by altering the inlet charge temperature, EGR rate, and fuel injection time and pressure. PCCI combustion has used a variety of fuel patterns, including early single pulse injection, port fuel injection, advanced multiple injections, and advanced injection with a tiny amount of late injection. In the previous section, the effects of early and late injection timings were explored. The modest amount of late injection is mostly used to reduce smoke emissions [49]. The spray angle of 70° was employed to atomize the fuel within the combustion chamber in order to eliminate wall wetness during advanced injection [49]. To avoid the generation of HC and CO emissions, the compression ratio of the PCCI engine was kept at the same level as that of a regular diesel engine. Due to the low volatility and strong flammability of the fuel, PCCI combustion has several limitations, according to a few studies [50].

For low volatile fuels like kerosene, diesel, and biofuels, spark assisted PCCI combustion has been applied. When compared to conventional CI combustion, the use of low-quality cetane fuel in the spark aided PCCI strategy engine enhanced engine performance [51]. The partially premixed combustion mixture is generated in PCCI-DI dual-mode combustion by injecting a large volume of fuel in the intake port or early pilot injection, followed by conventional direct injection of the same or another fuel. Due to the ignition delay interval, the combustion phasing of the PCCI-DI dual-mode combustion is primarily determined by the pilot fuel quantity, and the combustion rate is determined by the pilot fuel ratio [31]. For premixed compression ignition low-temperature combustion, port fuel injection is preferred (PCI-LTC). To create a premixed mixture with a proper air-fuel ratio, single fuel or dual fuel port injection is employed. Dual fuel premixed LTC has a better brake thermal efficiency than single fuel LTC and has achieved a significant reduction in NOx and soot emissions. The single fuel premixed LTC has a higher cycle to cycle variance due to the low temperature and lean air-fuel ratio [52, 53]. Reactivity controlled compression ignition (RCCI) is the name given to the dual-fuel premixed LTC, and a thorough description of the RCCI will be given in the following sections.
