The outlook for fuels for internal combustion engines

Abstract

The demand for transport energy is increasing, but this increase is heavily skewed toward heavier fuels such as diesel and jet fuel while the demand for gasoline might decrease. As spark-ignition engines develop to become more efficient, abnormal combustion such as knock and preignition will become more likely. High antiknock quality fuels, those with high research octane number and preferably low motor octane number, will enable future spark-ignition engines to reach their full potential. Higher fuel antiknock quality is also likely to mitigate “superknock” resulting from preignition—an abnormal combustion problem in turbocharged spark-ignition engines. In many parts of the world, fuel antiknock specifications are set on the assumption that higher motor octane number contributes to increased knock resistance. Specifications for fuel antiknock quality have a great impact on fuels manufacture and will need to be revised as this mismatch between existing specifications and engine requirements widens. The primary challenge for diesel engines is to reduce emissions of soot and NOx while maintaining high efficiency, and this becomes much easier if such engines are run on fuels of extremely low cetane. Significant development is needed before such engines can be seen on practical vehicles. In the long term, compression ignition engines are likely to use fuels with research octane number in the range of 70–85 (cetane number<∼30) but with no strict requirements on volatility. Such fuels would require less processing in the refinery than today’s fuels. Such an engine/fuels system will be at least as efficient as today’s diesel engine but could be significantly cheaper and also open a path to mitigate the imbalance in demand growth between heavy and light fuels that is expected to arise otherwise. The review concludes with a possible long-term fuel scenario.

Effects of In-Cylinder Mixing on Low Octane Gasoline Compression Ignition Combustion

“…The experimentally observed string-like structure of hollow-cone spray favors the KH-RT models since the spray is considered many small solid cone injections along a circular liquid sheet. Therefore, the initial SMD of the string-like liquid film is calculated by assuming that the cylindrical liquid blobs are attached to each other: (4) For the liquid jet stability analysis to be valid, the cylindrical liquid blobs must be detached from each other, but Eq. (4) serves as a starting point for the implementation of non-LISA breakup models for hollow-cone sprays.…”

“…The demand on global transport energy is expected to increase by around 40% by 2040 [1,2,3,4]. This large increase in demand will primarily be in non-organization for economic co-operation and development (OECD) countries.…”

Evaluation of Anti-Knock Quality of Dicyclopentadiene-Gasoline Blends

“…However, increased speed decreases residence time, which thereby reduces reactivity of the fuel air mixture. The empirical constant K, defined by Kalghatgi [3], for the PRF mixtures greater than RON of 75 would be lower for the engine operating at 900 rpm and 149°C than at 600 rpm and 52°C operating in HCCI mode. This is opposite to the actual RON and MON tests were K is greater at 900 rpm and 149°C.…”

“…The efficiency of spark ignited engines is connected to the fuel octane index (OI = RON -K*S), where RON is the research octane number, S is the octane sensitivity, and K is an empirical constant that depends on engine operating conditions [2]. Increasing the OI of a fuel would maximize tank-to-wheel carbon reductions [3]. However, refinery processes associated with increasing the fuel's anti-knock quality may have an adverse effect on well-to-tank efficiency and cost, depending on the composition of the blend stocks [4].…”

Analysis of combustion concepts in a poppet valve two-stroke downsized compression ignition engine designed for passenger car applications

“…This is explained by the fact that aromatic fuels become relatively more resistant to autoignition compared to paraffinic fuels as the pressure increases while the temperature is held constant, confirming that the true autoignition quality of gasoline-like fuels cannot be determined by just one number like CN or RON at all operating conditions. Another interesting remark is that for the conditions studied, if two fuels had the same ignition and combustion delay at a given operating condition, they exhibited comparable emissions and maximum pressure rise rates regardless of the differences in volatility or fuel composition [129,130]. Thus, for PPC the autoignition quality of a given fuel appears to be far more important than its volatility or composition in this type of combustion.…”