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In this research, there are two major sections for analysis: the characteristics of gasoline and diesel dual-fuel combustion and their application to operating load extension with high thermal efficiency and low emissions. All the experiments were completed using a single-cylinder compression ignition engine with 395 cc displacement. In the first section, the dual-fuel combustion modes were classified into three cases by their heat release rate shapes. Staying at 1500 r/min with a total value of 580 J of low heat for each cycle condition, the diesel injection timing was varied from before top dead center with a 6–46 °crank angle with 70% of gasoline fraction based on the low heating value. Among the modes were two suitable dual-fuel combustion modes for a premixed compression ignition. The first suitable mode shows multiple peaks in the heat release rate (mode 2) and the second suitable mode shows a single peak with a "bell-shaped" heat release rate (mode 3). These two dual-fuel combustion types showed a high gross indicated thermal efficiency of up to 46%. Based on the results in the first section, the practical application of dual-fuel premixed compression ignition combustion was investigated considering a high thermal efficiency and a high-load condition. At a 1500 r/min/gross indicated mean effective pressure of 6.5 bar, 48% of the gross indicated thermal efficiency was obtained by using dual-fuel premixed compression ignition combustion mode 3. This mode was typical of a "reactivity controlled compression ignition," while the nitrogen oxides and the particulate matter emissions satisfied the EURO-6 regulation (0.21 g/kW h and 2.8 mg/m3, respectively). In addition, a high thermal efficiency (45%) with low maximum pressure rise rate, NOx (nitrogen oxides), and particulate matter emissions was obtained at 2000 r/min/gross indicated mean effective pressure 14 bar condition by the adjustment of dual-fuel premixed compression ignition combustion mode 2. As a result, this research contributes to the understanding and practical application of dual-fuel combustion for a light-duty compression ignition engine. [ABSTRACT FROM AUTHOR]

The diesel compression ignition (CI) engine has higher durability and thermal efficiency than the gasoline spark ignition (SI) engine. However, the high levels of nitrogen oxides (NOx) and particulate matter (PM) emissions are major problems of diesel engines due to the auto-ignition of heterogeneous mixtures. The dual-fuel combustion concept could be solution to environmental concerns. Dual-fuel combustion can be implemented by substituting some of the diesel fuel with high-volatility fuels, such as gasoline and natural gas. The premixed mixture condition can be improved to diminish localized rich and stoichiometric regions. Notably, ethanol has greater potential to reduce PM emissions because it is highly volatile and readily oxidized. For these reasons, in this research, the effects of varying the ethanol substitution ratio on engine performance and emissions under the dual-fuel combustion condition were experimentally investigated under various load conditions. The test engine was a heavy-duty single-cylinder diesel engine with two direct injectors. Engine speed was fixed at 1000 rpm and the load condition was varied for an indicated mean effective pressure (IMEP) ranging from 0.2 to 0.8 MPa. The ratio of ethanol to the total input energy was controlled from zero to nearly 50% of the input energy. The NOx and PM emissions decreased with increasing ethanol substitution and the mean size of the PM emissions decreased. For the mid-load condition (IMEP 0.6 MPa), the substitution was increased to 63%, but for low and high loads, higher ethanol fractions could not be used because of insufficient ignition energy at low loads and sharp increment of the in-cylinder pressure under high loads. [ABSTRACT FROM AUTHOR]

In this research, the effects of three operating parameters (Diesel injection timing, propane ratio, and exhaust gas recirculation (EGR) rates) in a diesel-propane dual fuel combustion were investigated. The characteristics of dual-fuel combustion were analyzed by engine parameters, such as emission levels (Nitrogen oxides (NO) and particulate matter (PM)), gross indicated thermal efficiency (GIE) and gross IMEP Coefficient of Variance (CoV). Based on the results, improving operating strategies of the four main operating points were conducted for dual-fuel PCCI combustion with restrictions on the emissions and the maximum pressure rise rate. The NOx emission was restricted to below 0.21 g/kWh in terms of the indicated specific NO (ISNO), PM was restricted to under 0.2 FSN, and the maximum pressure rise rate (MPRR) was restricted to 10 bar/deg. Dual-fuel PCI combustion can be available with low NO, PM emission and the maximum pressure rise rate in relatively low load condition. However, exceeding of PM and MPRR regulation was occurred in high load condition, therefore, design of optimal piston shape for early diesel injection and modification of hardware optimizing for dual-fuel combustion should be taken into consideration. [ABSTRACT FROM AUTHOR]

Reactivity controlled compression ignition (RCCI) is one of representative dual-fuel combustion concepts for low NOx, soot emissions and high thermal efficiency. Overall lean and highly premixed auto-ignition combustion make low combustion temperature and the reduction of heat transfer loss. Although premixed compression ignition (PCI) combustion using a single fuel, i.e., diesel, also shows low emissions and higher thermal efficiency, combustion characteristics of RCCI (dual-fuel PCI) are different from single-fuel PCI due to reactivity gradient from two different fuel characteristics as well as local equivalence ratio due to the fuel distribution. Therefore, it is necessary to know the influence of above two factors on the dual-fuel combustion characteristics for better understanding of dual-fuel combustion and its effective utilization. In this research, the characteristics of dual-fuel combustion are evaluated comparing to single-fuel combustion. Also, dual-fuel combustion modes are classified according to the analysis of heat release rate (HRR) shapes. Major factors in the classification of dual-fuel combustion modes are the degree of fuel reactivity gradient and the local equivalence ratio in the cylinder. Thus, the diesel injection timing, diesel and port injected gasoline fuel ratios and the overall equivalence ratio were selected as the main variables to characterize each dual-fuel combustion mode. The result emphasizes that the dual-fuel combustion could be classified as three types by HRR shapes, and it was mainly affected by reactivity gradient and overall equivalence ratio. [ABSTRACT FROM AUTHOR]

The key point of premixed compression ignition (PCI) combustion is an ignition delay time that is sufficient to premix the air and fuel. Thus, when PCI combustion is implemented with a single fuel, a very early start of injection (SOI) is usually applied, along with heavy exhaust gas recirculation. However, if two different fuels are used simultaneously for PCI combustion, it is possible to control the in-cylinder fuel reactivity by adjusting their ratio. Because an additional ignition delay control parameter is used for dual-fueled PCI combustion, its operating strategy and combustion characteristics differ from those of single-fueled PCI combustion. In this study, single-fueled and dual-fueled PCI combustions were compared using gasoline and diesel fuel under part-load conditions (1500 rpm and a low heating value of 580 J/str). In both cases, the diesel SOI was varied from the top dead center (TDC) to 35° BTDC to analyze the combustion characteristics. Under the optimized operating conditions, the target engine-out emissions were below the gross indicated specific NOx (gISNOx) of 0.4 g/kWh and gISsmoke of 20 mg/kWh. The results showed dual-fueled combustion is more suitable for PCI conditions than single-fueled combustion in terms of both the engine-out emissions and gross indicated thermal efficiency. • Combustion characteristics were compared between single-and dual-fueled. • Energy fraction analysis were verified under single-and dual-fueled. • Strategies for single- and dual-fueled premixed combustion were suggested. • Dual-fueled combustion was superior to single-fueled aspect of premixed combustion. [ABSTRACT FROM AUTHOR]

• Effects of fuel fractions and diesel SOI on THC are discussed. • Methane is related with crevice effect and bulk quenching. • NMHC is related with wall-wetting of diesel spray. • MFB50 position has strong influence on heat transfer loss. • RCCI improved the BTE with reduction of THC emissions. In dual-fuel combustion, the levels of total hydrocarbon (THC) emissions have increased, unlike the neat diesel compression ignition (CI) combustion. Intuitively, it can be inferred that most THC emissions are produced by the crevice effect of low-reactivity fuels (high-volatility fuels) under dual-fuel combustion. Additionally, it is possible that high levels of THC emissions are produced by dual-fuel combustion. If reactivity-controlled compression ignition (RCCI) combustion is applied by advancing the diesel injection timing to improve the premixing conditions, the occurrence of the wall-wetting effect may induce the production of high levels of THC emissions owing to incomplete combustion. Thus, in this study, the characteristics of non-methane hydrocarbons (NMHC) and methane emissions under general dual-fuel combustion conditions (diesel injection timings before top dead center (BTDC) 0 and 30 crank angle degree (CAD)) and RCCI conditions (diesel injection timings at 60 and 84 CAD BTDC) were investigated under a low-load in a 6-L heavy-duty engine. The natural gas fraction varied from 50% to the maximum level considering the combustion stability (coefficient of variance of indicated mean effective pressure). The results revealed that the overall THC emissions from the general dual-fuel combustion were higher compared with those of RCCI combustion, owing to the methane emissions from the squish area and the lower average in-cylinder temperature. Notably, methane emissions were dominant in the THC emissions (52–87%) under the general dual-fuel combustion condition, while NMHC emissions were a major part of the in THC emissions (61–87%) under the RCCI regimes. Hence, combustion inefficiency is a major concern in dual-fuel combustion. In this study, this problem was resolved by advancing the diesel injection timings. The findings in this study can be useful in the design of oxidation catalysts, regardless of whether the combustion regime is a general dual-fuel combustion or RCCI combustion considering the portion of methane emissions in the exhaust gas. Additionally, it is known that the RCCI combustion is superior to the general dual-fuel combustion with respect to higher thermal efficiency and low harmful THC emissions. [ABSTRACT FROM AUTHOR]