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Lean burn is regarded as one of the most effective ways to improve fuel efficiency for spark ignition engines. However, the excessive air dilution deteriorates combustion stability, limiting the degree of engine operational dilution. The intensified flow field is therefore introduced into the cylinder to mitigate the decline of the burning velocity caused by the leaned-out fuel-air mixture. In a moderate flow field, flame kernels are formed near the hot spark plasma during discharge and stick to the spark gap even after the end of discharge; the flame front then propagates outward and evolves into self-sustained flame. Flame attaching to the spark gap is a common phenomenon in the early combustion stage and has been reported to be beneficial for flame inception in the literature.

Advanced ignition systems with enhanced discharge current have been extensively investigated in research, since they are highly regarded as having the potential to overcome challenges that arise when spark-ignition engines are running under lean or EGR diluted conditions. Local flow field is also of particular importance to improve the ignitability of the air-fuel mixture in SI engines as the spark plasma channel can be stretched by the flow across the spark gap, leading to longer plasma length, thus more thermal spark energy distributed to the air-fuel mixture in the vicinity of the spark plug. Research results have shown that a constantly high discharge current is effective to maintain a stable spark plasma channel with less restrikes and longer plasma holding period.

The control of nitrogen oxide and smoke emissions in diesel engines has been one of the key researches in both the academia and industry. Nitrogen oxides can be effectively suppressed by the use of exhaust gas recirculation (EGR). However, the introduction of inert exhaust gas into the engine intake is often associated with high smoke emissions. To overcome these issues there have been a number of proposed strategies, one of the more promising being the use of low temperature combustion enabled with heavy EGR. This has the potential to achieve simultaneously low emissions of nitrogen oxide and smoke. However, a quantitative way to identify the transition zone between high temperature combustion and low temperature combustion has still not been fully explored. The combustion becomes even more complicated when ethanol fuel is used as a partial substitution for diesel fuel.

Advances in engine technology in recent years have led to significant reductions in the emission of pollutants and gains in efficiency. As a facet of investigations into clean, efficient combustion, the homogenous charge compression ignition (HCCI) mode of combustion can improve upon the thermal efficiency and nitrogen oxides emission of conventional spark ignition engines. With respect to conventional diesel engines, the low nitrogen oxides and particulate matter emissions reduce the requirements on the aftertreatment system to meet emission regulations. In this paper, n-butanol, an alcohol fuel with the potential to be derived from renewable sources, was used in a light-duty diesel research engine in the HCCI mode of combustion. Control of the combustion was implemented using the intake pressure and external exhaust gas recirculation. The moderate reactivity of butanol required the assistance of increased intake pressure for ignition at the lower engine load range.

Substantial effort has been devoted to utilizing homogeneous charge compression ignition (HCCI) to improve thermal efficiency and reduce emission pollutants in internal combustion engines. However, the uncertainty of ignition timing and limited operational range restrict further adoption for the industry. Using the spark-assisted compression ignition (SACI) technique has the advantage of using a spark event to control the combustion process. This study employs a rapid compression machine to characterize the ignition and combustion process of Dimethyl ether (DME) under engine-like background temperature and pressures and combustion regimes, including HCCI, SACI, and knocking onsite. The spark ignition timing was swept to ignite the mixture under various thermodynamic conditions. This investigation demonstrates the presence of four distinct combustion regimes, including detonation, strong end-gas autoignition, mild end-gas autoignition, and HCCI.

Reduction of nitrogen oxides (NOx) in lean burn and diesel fueled Compression Ignition (CI) engines is one of the major challenges faced by automotive manufacturers. Lean NOx Trap (LNT) and urea-based Selective Catalytic Reduction (SCR) exhaust after-treatment systems are well established technologies to reduce NOx emissions. However, each of these technologies has associated advantages and disadvantages for use over a wide range of engine operating conditions. In order to meet future ultra-low NOx emission norms, the use of both alternative fuels and advanced after-treatment technology may be required. The use of an alcohol fuel such as n-butanol or ethanol in a CI engine can reduce the engine-out NOx and soot emissions. In CI engines using LNTs for NOx reduction, the fuel such as diesel is utilized as a reductant for LNT regeneration.

Advanced combustion engines, as power sources, dominate all aspects of the transportation sector. Stringent emission and fuel efficiency standards have promoted the research interest in advanced combustion strategies and alternative fuels. Owing to the comparable energy density to the existing fossil fuels and renewable production, alcohol and ether fuels may be a suitable replacement, or an additive to the gasoline/diesel fuels to meet the future emission standards with minimal modification to current engine geometry. Furthermore, lean and diluted combustion are well-researched pathways for efficiency improvement and reduction of engine-out emissions of modern engines. However, lean-burn or EGR dilution can introduce combustion inefficiencies in the form of excessive hydrocarbon, carbonyl species and carbon monoxide emissions.