The effects of three kinds of oxygenated fuel blends—i.e., ethanol-gasoline, n-butanol-gasoline, and 2,5-dimethylfuran (DMF)-gasoline-on fuel consumption, emissions, and acceleration performance were investigated in a passenger car with a chassis dynamometer. The engine mounted in the vehicle was a four-cylinder, four-stroke, turbocharging gasoline direct injection (GDI) engine with a displacement of 1.395 L. The test fuels include ethanol-gasoline, n-butanol-gasoline, and DMF-gasoline with four blending ratios of 20%, 50%, 75%, and 100%, and pure gasoline was also tested for comparison. The original contribution of this article is to systemically study the steady-state, transient-state, cold-start, and acceleration performance of the tested fuels under a wide range of blending ratios, especially at high blending ratios. It provides new insight and knowledge of the emission alleviation technique in terms of tailoring the biofuels in GDI turbocharged engines. The results of our works showed that operation with ethanol–gasoline, n-butanol–gasoline, and DMF–gasoline at high blending ratios could be realized in the GDI vehicle without any modification to its engine and the control system at the steady state. At steady-state operation, as compared with pure gasoline, the results indicated that blending n-butanol could reduce CO₂, CO, total hydrocarbon (THC), and NO_X emissions, which were also decreased by employing a higher blending ratio of n-butanol. However, a high fraction of n-butanol increased the volumetric fuel consumption, and so did the DMF–gasoline and ethanol–gasoline blends. A large fraction of DMF reduced THC emissions, but increased CO₂ and NO_X emissions. Blending n-butanol can improve the equivalent fuel consumption. Moreover, the particle number (PN) emissions were significantly decreased when using the high blending ratios of the three kinds of oxygenated fuels. According to the results of the New European Drive Cycle (NEDC) cycle, blending 20% of n-butanol with gasoline decreased CO₂ emissions by 5.7% compared with pure gasoline and simultaneously reduced CO, THC, NO_X emissions, while blending ethanol only reduced NO_X emissions. PN and particulate matter (PM) emissions decreased significantly in all stages of the NEDC cycle with the oxygenated fuel blends; the highest reduction ratio in PN was 72.87% upon blending 20% ethanol at the NEDC cycle. The high proportion of n-butanol and DMF improved the acceleration performance of the vehicle.

The current brake thermal efficiency of advanced internal combustion engines is limited to 50%, and how to further improve the efficiency is a challenge. In this study, a theoretical investigation on engine thermal efficiency was carried out using one-dimension simulations based on the first law of thermodynamics. The energy balance was evaluated by varying parameters such as compression ratio (CR); heat transfer coefficient; intake charge properties; and combustion phasing etc.—their influences on the efficiency limits were demonstrated. Results show that for a given heat transfer coefficient, an optimal CR exists to obtain the peak efficiency. The optimal CR decreases with the increase of heat transfer coefficient, and high CR with a low heat-transfer coefficient can achieve a significantly high efficiency. A higher density and specific heat ratio of intake charge, as well as a shorter combustion duration with a proper CA50 (crank angle at 50% of total heat release), can increase efficiency significantly. Methanol shows an excellent ability in decreasing the peak in-cylinder temperature; and the peak indicated efficiency is relatively higher than other tested fuels. The displacement has few effects on the indicated efficiency, while it shows a strong effect on the energy distribution between heat transfer and exhaust energy. All these strategies with high CR result in high in-cylinder pressure and temperature; which means a breakthrough of material is needed in the future.

Coal to liquid (CTL) is one of the potential methods to obtain the alternative fuel used in diesel engines. There are two methods to obtain alternative fuel from coal, namely, indirect and direct liquefaction processes. This paper evaluates the effects of indirect coal-to-liquid (ICL) fuel and direct coal-to-liquid (DCL) fuel on the combustion, performance, and emissions on a heavy-duty diesel engine. The engine was run at 1,200 and 2,000 rpm without exhaust gas recirculation (EGR) and three engine loads (25, 50, and 75%) were operated at each speed. Three injection pressures (80, 100, and 160 MPa) were applied. Results show that the cetane number is the dominating factor in heat-release patterns at the light load; however, the difference of cetane number between CTL fuels and diesel only has a minor effect on ignition delay at high loads. The brake specific fuel consumption (BSFC) of ICL is lower than that of diesel fuel, while the BSFC of DCL is higher than that of diesel fuel. The brake thermal efficiency (BTE) values of two CTL fuels are lower than that of diesel baseline due to their poor lubricity and lower mechanical efficiency. The soot emissions of ICL are always lower than those of diesel fuel at all tested operating conditions. However, the soot emissions of DCL are lower than those of diesel fuel at the low load but a little higher than those of diesel fuel at the high load. The NOx emissions of ICL fuel are lower than those of the other two fuels under low injection pressure, while the NOx emissions of ICL are a little higher than those of diesel fuel at high injection pressure but lower than those of DCL. Unburned hydrocarbons and carbon monoxide emissions of both CTL fuels remain low under both light- and high-load conditions. In general, ICL fuel is more preferable than DCL and diesel fuel from the perspectives of engine performance and emissions.

Optical diagnostics is an effective method to understand the physical and chemical reaction processes in homogeneous charge compression ignition (HCCI) and low temperature combustion (LTC) modes. Based on optical diagnostics, the true process on mixing, combustion, and emissions can be seen directly. In this paper, the mixing process by port‐injection and direct‐injection are reviewed firstly. Then, the combustion chemical reaction mechanism is reviewed based on chemiluminescence, natural‐luminosity, and laser diagnostics. After, the evolution of pollutant emissions measured by different laser diagnostic methods is reviewed and the measured species including NO, soot, UHC, and CO. Finally, a summary and the future directions on HCCI and LTC used optical diagnostics are presented.

An active prechamber turbulent ignition system is a forced ignition method for internal combustion engines fueled with low reactivity fuels, i.e., natural gas and gasoline, which could expand the lean-burn limit, promote flame propagation, and ensure cyclic stability. In the present study, the effects of charge concentration stratifications inside the prechamber on the jet characteristics and combustion process were numerically investigated using CONVERGE software coupled with a reduced methane mechanism by the coupling control of spark timing and prechamber global equivalence ratio. The results show that the jet characteristics and ignition mechanisms can be regulated by controlling the prechamber global equivalence ratio and spark timing. On the one hand, as the prechamber global equivalence ratio increases, the velocity of the jet increases firstly and then decreases, the temperature drops, and OH and CH₂O radicals are reduced, but the stable combustion intermediates, CO and H₂, are increased. Thus, the ignition mechanism changes from flame ignition (ignition by flame and reactive radicals) to jet ignition (ignition by hot combustion intermediates), and the ignition delay is shortened, but the combustion duration is extended, mainly due to more of the combustion intermediates, CO and H₂, downstream of the jet. On the other hand, as spark timing is advanced, the jet velocity and the mass of the OH and CH₂O radicals increase, which is conducive to flame ignition, and the ignition delay and combustion duration are reduced.

In order to meet stricter emissions regulations and fuel consumption regulations, the upgrading of fuel quality has become one of the most important trends in the development of internal combustion engines. In this article, 89 # gasoline (G89) that is available on the Chinese market was selected as the base fuel, and five unconventional additives, ethyl tert-butyl ether (ETBE), N-Methylaniline, sec-butyl acetate, p-methylphenol and isobutanol, were added to the base fuel and named as G89-1, G89-2, G89-3, G89-4 and G89-5, respectively. The effects of these unconventional additives on a PFI vehicle were investigated. The test was carried out on a chassis dynamometer and the NEDC cycle was adopted to simulate driving conditions. The results show that, in terms of fuel consumption, G89-3 showed the best performance for decreasing fuel consumption. In terms of gaseous emissions, G89-4 decreased all four gaseous emissions, CO₂, CO, THC and NOx, to a greater extent, which indicates that blending p-methylphenol into gasoline has a better potential for the vehicle to achieve cleaner emissions. In terms of acceleration performance, the five additives all shortened the acceleration time. The effects of the different additives on shortening acceleration time are basically consistent with the RON of the fuel.