No abstract

Recently, there has been an increasing awareness of environmental and energy problems, which are global in scale. Diesel engines have better fuel consumption than gasoline engines, and there are great hopes for them because they are more flexible in terms of fuel diversification. However, diesel engines have more NOx and smoke than gasoline engines, and thus require expensive fuel injection components and emission control devices to clean these emissions. Inagaki et al. 1) proposed a new combustion concept that reduces NOx significantly below the Euro6 standard by operating PCCI (Premixed Charge Compression Ignition) in diesel engines that have highly dispersed spray from injectors with numerous small-diameter orifices with a narrow angle combined with low in-cylinder flow. A schematic diagram of an engine for the new combustion concept is shown in Fig. 1, and the basic specifications of the engine are shown in Table 1. The engine is based on a direct-injection diesel engine found in commercially available vehicles in Europe. A low pressure loop (LPL) EGR system was added to the original engine, which has a conventional high pressure loop (HPL) EGR system. The engine for the new combustion concept is using conventional diesel engine injection components to control costs, and have multi-orifice nozzles with orifices that are smaller than in conventional diesel engines. This type of nozzles with numerous small-diameter orifices can form the highly dispersed spray which can promote the entrainment under the restricted in-cylinder flows.

Hashizume(i), Shinobu Ishiyama(]), rfakashi Ogawa(i), Masaaki Kono(2), and Kazuhisa Inagaki(3)rferutoshi Ibmoda(i),

It has been respected to realize large-scale natural-gas engines. Low flame-propagation speed and poor spatial in-cylinder penetration of gaseous fuels impede the large-scale natural-gas practical. Premixed compression-ignition (homogeneouscharge compression-ignition, HCCI) engines have not such kind of problems, because natural-gas and air are supplied as mixtures, and burn out through speedy knocking-like combustion. However, a very narrow operating range could be established due to a lack of autoignition-timing control procedures. A formaldehyde-assisted premixed-compressionignition natural-gas engine concept has been proposed previously by the authors [1] to realize large scale natural-gas engines having ignition-timing control procedures.Generation/consumption histories of chemical species during the preflame induction period approaching to the final hot-flame ignition were investigated concerning the formaldehyde-assisted compression-ignition natural-gas engine.Small amount of formaldehyde is supplied as an additive into the premixed intake charge of natural gas and air. The formaldehyde addition has a strong promoting effect for lean mixture ignition of natural gas. When suitable amount of formaldehyde, even a hundreds ppm order of magnitude, is added into the intake fuel/air mixture the pistoncompression ignition will occur adequately near the top dead center. This procedure enabled us to obtain ignition or hot-flame explosion even of the fuel/air mixtures nonflammable through a simple piston compression. The formaldehyde acts efficaciously as the ignition-promoting additive for the methane-based gaseous fuels which are weak in cool-flame generation during the preflame induction periods. Natural gas is a typical one of this kind.The in-cylinder gas composition histories were obtained by gas sampling / analyzing processes with a magnetic operating valve and gas chromatographs, concerning mainly to the methane, carbon monoxide, carbon dioxide and formaldehyde. Experiment was carried out using a single cylinder engine and a commercial natural gas 13A.The formaldehyde concentration shows a slight rise followed by prompt decrease at the final stage of the ignition delay period; so-called blue-flame period, but seemingly stable during almost the whole induction period up to the ignition.A piston compression of a simple charge of natural gas and air with no intake formaldehyde addition showed a gradual formaldehyde generation during the preflame period and sometimes slight consumption at the final stage before the hotflame occurrence.When the intake air is mixed with formaldehyde only, i.e., no fuel is included, the formaldehyde is consumed briskly near the top dead center, and shows a small but recognizable pressure rise due to a heat release.The effect of formaldehyde added into the fuel/air mixture leading to the ignition would not be an event antecedent to the natural gas preflame reaction but a promoting event of the preflame reaction of the main natural gas fuel.It is demonstrated that during the induction...