J-090715-1Combustion and emission characteristics of DME as an alternative fuel for compression ignition engines Fuel 87 (2008) 2779–2786

1 DME, it canbe used for compression ignition engines which have higherthermal efficiencies compared to spark ignition engines.Teng et al. [3] estimated the cetane number for DME tobe 68, a value that is much higher than that of conventionaldiesel fuel (40–56).

2 he higher cetane numberof DME offers mild engine operation with lower enginenoise because it reduces ignition delay and suppresses rapidpremixed burning

3 Many researchers [4–6] have reported lowerhydrocarbon (HC) and carbon monoxide (CO) exhaust emissions as well as soot free combustion for DME fueledengines. On the other hand, emissions of oxides of nitrogen(NOx) from the DME fueled engines are known to be significantcompared to other emissions [5,6].

4 Previous research [7] on the characteristics of DMEinjected through a high pressure common-rail injection systemindicates that the DME spray has a smaller dropletdiameter than that of diesel fuel under the same injectionconditions because of its lower surface tension.

5 Moreover, the rapid droplet evaporationof DME leads to the apparent turbulent-jet-like behaviorof the spray [3,8]..

6 alubrication improver (Lubrizol 539M, Lubrizol)

7 In order to determine the relationship between the pulsewidth of the injector and the mass of fuel supplied to theengine, the discharging mass flow rate was obtained bymeasuring the mass of the fuel tank. The accumulated massof fuel injected during 5000 cycles was weighed using anelectronic precision balancer (GP-30K, AND).

8 Fuel temperature (C) 20

9 the pulse width ofthe injector was determined from its relationship to themass of fuel supplied to the engine, which was obtainedfrom the previously described measurement of injectionmass.

10 a DME equivalent of11.9 mg due to its lower heating value.

11 Compression ratio 17.8

12 Spray angle (C) 156

13 Mass of fuel (mg/cycle) DME 11.9

14 Pulse duration (ls) DME 784

15 Although the pulse width was thesame for both fuels, DME was injected slightly faster (by0.02 ms) and ended later (by 0.1 ms) than diesel as shownin Fig. 2a. As a result, the actual injection duration ofDME was longer than that of diesel under the same injectioncondition.

16 start of injection pulse of 8

17 The rate of heat release also indicates DMEfuel was ignited faster and the premixed burn spike waslower than that of diesel fuel. The shorter ignition delayand lower energy supply rate explains the lower peak heat release of DME.shorter ignition delay because high centane number.

18 Although the mixing rate ofDME with air is lower than that of diesel fuel [4,8,9], areduced late combustion region was indicated due tothe faster evaporation of DME. shorter late combustion.

19 In the caseof DME fueling, the DME fueled engine presents ahigher premixed spike at an injection of 2 BTDC thanat 8 BTDC. This can be explained because the retardedinjection timing extended ignition delay, as a result, theaccumulated energy between the start of injection andstart of combustion was increased.

20 Due to the shorter ignitiondelay of DME fuel, excessive rise in pressure caused both (1) by chemical reactions occurring before combustion andby (2) the products produced during the ignition delay burning

21 the engine can beoperated under more delayed injection timing for a reductionof NOx emission compared to the engine operatingcondition with diesel fueling.

22 As the injection timingadvanced, IMEP decreased because the main heat releasewas created during the compression stroke; accordingly,negative work during compression stroke increased.

23 The higher IMEP of DMEindicates higher efficiency, and there are several reasonsfor this. First, contrary to the flame of diesel combustion,a non-luminous flame was found for DME [15]. Consequently,a lower heat radiation of the DME flame mightreduce cooling loss through the wall of the combustionchamber. Second, the combustion efficiency which canbe defined as a ratio of the fuel’s chemical energy andactual heat release during combustion is higher forDME due to the lower fraction of incomplete combustionproduct such as HC and CO.

24 In the range of injection timing between 15 and 2BTDC, lower COVIMEP of DME was observed as shownin Fig. 6a. This means that the DME engine operates morestably than the diesel fueled engine.

25 Higher NOx emissions throughout the injection timingwere observed and compared to diesel fuel. It can beexplained because the faster ignition of the DME mixtureleads to an increased charge temperature compared todiesel fuel.

26 lower exhaust gas temperature as seen in the figure.This result was affected by faster ignition and areduced late combustion regime compared with dieselfueling. Lower HC and CO emissions and lower exhausttemperatures

27 Considering the lower tip penetration and fasterevaporation and ignition of DME, reduced fuel wall wettingis expected to result in lower HC emission.

28 [4] Kim MY, Bang SH, Lee CS. Experimental investigation of spray andcombustion characteristics of dimethyl ether in a common-rail dieselengine. Energ Fuels 2007;21:780–93.

29 [7] Kajitani S, Oguma M, Mori T. DME fuel blends for low-emission,direct-injection diesel engine. SAE Tech Pap Ser; 2000. 2000-01-2004.

30 [8] Suh HK, Park SW, Lee CS. Atomization characteristics of dimethylether fuel as an alternative fuel injected through a common-railinjection system. Energ Fuels 2006;20:1471–81.

31 [9] Teng H, McCandless JC. Comparative study of characteristics ofdiesel-fuel and dimethyl-ether sprays in the engines. SAE Tech PapSer; 2005. 2005-01-1723.

20

J-090714-1Engine Performance and Exhaust Characteristics of Direct-injection Diesel Engine Operated with DME (SAE 972973)

1 Because of its low self-ignition temperature (235°C),

2 Compression Ratio 17.7

3 the injection nozzle opening pressure was set at 8.82MPa (90kg/cm2) when the engine ran at 960rpm

4 Note that the recommended opening pressure of the engine for Diesel fuel, on the other hand, was 20.1MPa (205kg/cm2).

5 also in the operating conditions including the fuel feed pressure, which ranged from 1.96 to 2.94MPa (20 to 30kgf/cm2) in other studies.

6 injection time and the engine’s response, it was adjusted to occur at 17bTDC

7 have the opening start at 17bTDC, the actual (dynamic) opening occurred at 13bTDC for DME

8 This exhibited that the opening with DME occurred earlier than gas oil by as much as by four crank angle degrees (CA).

9 Two different injection times were studied, with settings of 17bTDC and 5bTDC (indicated by the manufacturer’s manual), which had one tooth difference between the gears in the engine and injection pump.

10 at the speed of 960rpm and the load to deliver (brake) mean effective pressure (mep) of 0.3MPa (Fig. 7), and mep = 0.6MPa

11 when the load was low (Fig. 7), the rapid pressure rise occurred earlier with DME than with gas oil by about the corresponding amount, although the peak pressure occurred almost at the same CA for both fuels. When the load was high (Fig. 8), the difference in start of pressure rise was even more obvious with DME compared with Diesel fuel. The earlier start of pressure rise in both experiments did not appear to occur due to an easy (chemical) ignition tendency of DME but more the differences in the start of nozzle lift.

12 When the injection time was delayed, the effect of self-ignition tendency of DME seemed to play a predominant role resulting in a far earlier start of pressure rise compared with Diesel operation.

13 The difference in EGT for the two fuels was rather significant, as much as over 50øC,

14 the engine with DME ran relatively quiet by observing that its premixed combustion stage was "milder" than that with the gas oil operation.

Mentioning the mild premixed combustion with DME and its impacts, it is realized that the low soot emission with DME (as shown later in Fig. 22) is not due to a great amount of fuel consumption in its premixed combustion stage, which is the case in the typical gas oil operated
Diesel engine producing a low soot emission.

15 the shorter the ignition delay (Fig.17), the milder the intensity of premixed combustion causing a quiet engine operation,

16 However, a common observation of a short ignition delay in a Diesel engine to produce high soot emissions is no longer true in the DME operated engine.

17 the injection of gas oil completed within a short period of time, particularly when the engine load is low,

18 The continuing combustion for DME at a high load, therefore, is caused by the prolonged injection period.

19 it seemed that the chemical aspect of fuel to produce low soot formation played a dictating role in producing low soot emissions.

20 Note that Glensvig and Sorenson [12] suggested that a DME spray completes the evaporation within a very short period of time after injection. In addition, the high stoichiometric fuel/air ratio will have a greatly diluting effect in a DME spray. Also, the extended injection period means a greater momentum imparted on the DME spray, making it more dispersed. These all are expected help produce a lean local fuel/air ratio, that is, to have lean combustion compared with a Diesel fuel spray.

21 Considerably high NOx emission was observed when the engine was operated by DME under the engine-manufacturer recommended injection time for gas oil, i.e., injection at 17bTDC injection time (Fig. 20). It is noted that this observation is in contrast with low NOx emission reported by others [7]. One of the most probable reasons for the high emission is considered to be the unusually early start of combustion with DME.

22 Note that the dispersed fuel spray formation with DME would help produce low NOx emission.

23 5bTDC, however, the NOx emission was much lower with DME. This finding is explained by the high rate fuel injection (mass of fuel/deg)

24 operation compared with its counter part (Fig. 15) producing high-temperature combustion products with the piston located still near the TDC.

25 The emission of THC from the DME-operated was very low regardless of injection time for a wide range of engine loads. This finding may be explained in terms of several parameters, including the average cylinder temperature (ACT), fuel-air ratio in the spray and chemical
characteristics of the fuel.

26 The dispersed locally lean fuel spray formation expected with DME, as explained earlier, may be a factor consuming the maximum amount of fuel before being wasted in the exhaust.

27 The emission of soot with DME operation was virtually zero (Fig. 22) under the entire experimental conditions investigated in the present study.

28 the fuel is highly volatile, becoming a gaseous jet or attaining a high specific volume as soon as leaving the injector, which transfers a greater amount of momentum during a longer period of injection compared to the gas-oil injection.

29 since DME is an oxygenate like a methanol, which is known to produce low soot in Diesel engines, it may not be difficult to expect a low soot emission by the fuel. Therefore, it seems be
reasonable to consider that the low soot with DME in Diesel engines is either or both the lean fuel/air spray structure and the fuel’s intrinsic tendency of low soot formation in Diesel engines.

30 7. Sorenson, S.C., Mikkelsen, S.E., "Performance and Emissions of a 0.273 Litter Direct Injection Diesel Engine Fueled with Neat Dimethyl Ether," SAE Paper 950064, 1995.

(转)The low-cost airline Ryanair charges a credit card fee of five euros each way and per person, which means that a family of six flying to Spain and

The low-cost airline Ryanair charges a credit card fee of five euros each way and per person, which means that a family of six flying to Spain and back will pay a colossal 60 euros in credit card fees. The only way around this by using a Visa Electron card. EasyJet doesn't charge for the use of Electron cards either, though their standard credit card fee is not as draconian as Ryanair's. On this page you can find details of if and how you can get a Visa Electron in the United Kingdom, Ireland, Spain and Germany.
See also: Ryanair Credit Card Fees - an airline spokesman defends the charge.
Visa Electron Cards in the UKBarclays, Smile (an internet bank) and Halifax will allow you to 'downgrade' your account to one with an Electron card. But this could cause you other problems, as not all vendors accept Electron.
The only bank I know of that will offer you both a standard debit card and an Electron card is Abbey.
Another option is to get a 'gift card' which, rather than being connected to your bank account, you 'charge it' with money. This usually involves a small commission, but not as much as Ryanair's credit card fees. Barclays, Natwest and the Post Office all have gift cards. The post office also has a 'Travel Money Card' which operates in a similar way.
The following banks in the UK no longer issue Electron cards: Lloyds, Nationwide, HSBC, Alliance and Leceister and Cooperative Bank.