it is quite all right, Premixed Charge Compression Ignition (PCCI) is a compromise between achieving the control of CIDI (Compression Ignition Direct Injection) combustion but with the exhaust gas emissions of HCCI, specifically soot. Homogeneous charge compression ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer (typically air) are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases chemical energy into a sensible form that can be transformed in an engine into work and heat.

the PCCI engine had the mixture time of fuel and air is shorter than that of HCCI engine. Some one defined HCCI is the engine which the mixture formation outside the combustion chamber (long time to mix - homogeneous mixture), and if the fuel injected directly inside the combustion chamber, it is PCCI. However, some author call Early Injection PCCI engine is HCCI engine

Actually PCCI is the hybrid of HCCI and diesel combustion,has more control on combustion/ignition and heat release rate with lower level of NOx and soot emission because premixed charge can be controlled with different fuel blending in different compositions to get optimum results/better control over ignition.

In HCCI combustion well mixed air and fuel enter the combustion chamber and are compressed to the point of auto-ignition. while in PCCI combustion fuel is injected in compression stroke and so we have the hybrid of HCCI and diesel combustion. in PCCI combustion we can use more EGR than HCCI.

To get high efficiency you need to have CI combustion. Current CI engines use diesel fuel which autoignites very soon after it is injected in the cylinder before it has had a chance to mix with oxygen in the cylinder and this causes high soot and NOx at the exhaust. PCCI combustion is a practical way of achieving low NOx and low soot in CI engines. NOx can be reduced by reducing combustion temperature.Soot formation can be avoided if the equivalence ratio wherever combustion occurs is below about 2. The engine- out soot reflects the balance between soot that is formed and the soot that is oxidised within the cylinder. In HCCI engiines very lean mixtures ensure low NOx and low soot- indeed in HCCI engines as equivalence ratio (load at a given speed)increases, NOx (and heat release rate) will increase and will eventually be too high. Also, HCCI engines have no in-cycle control over combustion phasing.

In diesel (practical CI) engines. NOx can be reduced by using EGR . However, if you use EGR, soot oxidation is inhibited and engine-out soot will increase. In premixed CI (PCI) combustion, if the final fuel injection, which controls combustion phasing, is completed sufficiently before combustion starts (high ignition delay), soot formation can be avoided in the first place and EGR can be used to control NOx.With conventional diesel fuel PCI combustion is possible only at very low loads. Increasing the injection pressure or reducing the cetane number of the fuel makes PCI combustion easier.

In summary, in PCCI (or PCI) combustion you are trying to get the benefits of HCCI combustion (low NOx,low soot and high efficiency) while retaining control over combustion phasing. The fuel and oxygen should be "premixed enough" to get these benefits but must not be fully premixed. The inhomogeneity in the cylinder achieved with late injection allows the engine to be run at conditions where HCCI combustion would not be possible.

in PCCI: Controlled of air fuel mixture before combustion, one step advance method than HCCI. 

PCCI combustion is a possible solution to the control and specific power challenges of HCCI engines. PCCI is a generalization of HCCI combustion where the fuel and air mixture may be partially stratified at the moment of ignition. 

In original meaning of words, HCCI combustion pursues 'entirely homogeneous' and air-fuel mixture should be ready to auto-ignite. On the other hand, PCCI (including PCI) combustion has more degree of freedom in view point of 'homogeneous degree'. PCCI combustion have not to be entirely homogeneous, but just ready to be 'premixed'.

So in my opinion, PCCI is one of practical approach toward HCCI combustion and we cannot compare two concepts on the same level.

Hello Taib Iskandar Mohamad ,

HCCI:

Homogeneous charge at equivalence ratio less than 0.5 is compressed and auto ignited. Note that the fuel is vaporized and this vapor is injected to premix with air in port.

Since, the charge is homogeneous => less soot formation

since, lean operation (lower temp.s) => less NOX

But there is no direct control on time of ignition, HRR which limits the maximum load on the engine and these are the disadvantages.

PCCI:

Before compression stroke influences, fuel is injected and time is provided to pre-mix the fuel and air. This pre-mix charge is then compressed.

So, in DICI---> after air is compressed and temp. is raised, fuel is injected to start ignition and combustion

in PCCI---->before the influence of compression begins, fuel is injected to premix (as in DICI) to premix well with air and that premix charge is compressed (as in HCCI) and combusted.

Simply, PCCI = DICI + HCCI

DI helps in control over time of ignition and HRR. But, more premix time implies more delay period. Therefore, if diesel is the fuel, knocking occurs. So, low reactive fuels only can be used.

Do you guys run some simulation about HCCI and PCCI models using Converge?