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The effects of intake pressure (Pin), start of injection (SOI), injection pressure (Pinj), injection split ratio (Qsplit), internal and external exhaust gas recirculation rates were varied to optimize several key parameters at a partially pre-mixed combustion low load/low speed condition using CFD. These include indicated specific fuel consumption (ISFC), combustion phasing (CA50), maximum rate of pressure rise (MRPR), maximum cylinder pressure (Pmax), indicated specific NOx (sNOx), indicated specific hydrocarbons (sHC) and Filter Smoke Number (FSN) emissions. Low-load point (6 bar indicated mean effective pressure (IMEP), 1500 revolutions per minute (RPM)) was selected where Pin varied between 1.25 and 1.5 bar, SOI between -100 and -10 crank angle degree (CAD) after top dead center (aTDC), Pinj between 100 and 200 bar, split ratio between 0 and 0.5, EGR between 0 and 45% and internal EGR measured by rebreathing valve height was varied between 0 and 4.5 mm.

Recent research [21] has shown that the compression ignition concept where very low cetane fuels (RON between 70 and 85) are run in compression ignition (CI) mode has several advantages. The engine will be at least as efficient and clean as the current diesel engines but will have a less complicated after-treatment system. The optimum fuel will be less processed and therefore simpler to make compared to current gasoline or diesel fuels. Naphtha, which is a product of the initial distillation of petroleum, is one such fuel. It provides a path to mitigate the global demand imbalance between heavier and lighter fuels that is otherwise projected. Since naphtha requires much less processing in the refinery than either gasoline or diesel [23], there is an additional benefit in terms of well-to-wheel CO2 emissions and overall energy consumed. Partially premixed charge compression ignition combustion with such a low cetane fuel has usually been investigated with a diesel engine base.

Demand for transport energy is growing but this growth is skewed heavily toward commercial transport, such as, heavy road, aviation, marine and rail which uses heavier fuels like diesel and kerosene. This is likely to lead to an abundance and easy availability of lighter fractions like naphtha, which is the product of the initial distillation of crude oil. Naphtha will also require lower energy to produce and hence will have a lower CO₂ impact compared to diesel or gasoline. It would be desirable to develop engine combustion systems that could run on naphtha. Many recent studies have shown that running compression ignition engines on very low Cetane fuels, which are very similar to naphtha in their auto-ignition behavior, offers the prospect of developing very efficient, clean, simple and cheap engine combustion systems. Significant development work would be required before such systems could power practical vehicles.

More stringent emissions standards along with higher fuel economy demands have obliged auto makers to develop technical solutions that exploit synergistic features from gasoline and diesel engines. To minimize NOx and soot trade-off, diesel powertrain has been developed to adopt increasingly complex and expensive technology such as extremely high pressure fuel injection systems, low pressure EGR, and variable valve timing. These attempts are associated with promoting Partially Premixed Charge Compression Ignition (PPC-CI) combustion via increasing mixing time and ignition delay. Alternatively, PPC-CI combustion can be achieved easier by using fuels with higher resistance to auto-ignition than conventional diesel fuel. Previous work has demonstrated the possibility of reducing the cost of future diesel after-treatment systems by using gasoline-like fuels.

Detailed combustion studies have historically been conducted in simplified reacting systems, such as shock-tubes and rapid compression machines. The reciprocating internal combustion engine presents many challenges when used to isolate the effects of fuel chemistry from thermodynamics. On the other hand, the conditions in such engines are the most representative in terms of pressure and temperature histories. This paper describes the use of a single-cylinder research engine as an advanced reactor to better determine fuel effects experimentally. In particular, a single-cylinder engine was operated in a manner that allowed the effects of changes in charge composition and temperatures to be isolated from changes in equivalence ratio. An example study is presented where the relative effects of low-temperature and high-temperature chemistry, and their effects on combustion phasing, are isolated and examined.