Homogenous-Charge Compression Ignition (HCCI)

This technology is essentially a combination of the operating principles of a gas engine and a diesel. When high power is required, an HCCI engine operates like a conventional gasoline engine, with combustion initiated by a spark plug. At more modest loads, it operates more like a diesel, with combustion initiated by the pressure and heat of compression.

In a diesel engine, combustion starts when the fuel is injected with the piston near the top of the compression stroke, and the combustion is controlled by the speed at which the fuel is injected. With HCCI, however, the fuel has already been injected and mixed with the air before the compression stroke begins.

Since compression alone initiates combustion, it’s more of a big bang than even a diesel’s hard-edged power stroke. Making the engine sturdy enough to avoid blowing apart makes an HCCI at least as heavy as a diesel. The key is achieving sufficient combustion control so that the HCCI cycle can be used over as wide a speed and load range as possible to get the efficiency benefits.

One way to extend the HCCI mode is to employ a variable compression ratio, which is what Mercedes has done on its experimental Dies-Otto engine. The payoff can be a 20-percent improvement in fuel economy without the particular traps and the NOx catalysts that diesels need. HCCI might make it into production by the end of this decade, perhaps as an efficient engine for a plug-in hybrid because it only needs to run over a small rpm band to power a generator.

Revised Stop-Start Systems

Turning off an engine when stopped at a light can definitely save fuel. It’s easy to program an engine-control computer to shut down an engine when the vehicle speed drops to zero and restart it when the driver removes his foot from the brake pedal. The starter and the battery might need to be improved to withstand more frequent use, but that’s no technical challenge.

Mazda has come up with a simpler method of accomplishing the stop-start feat. In its system, called i-stop, the computer stops the engine when one piston is just past the top of the compression stroke. To restart, fuel is injected into the cylinder, the spark plug is fired, and the engine is instantly running again.

Unfortunately, while these systems might save as much as five percent of fuel consumption in an urban setting, the EPA’s test cycles demonstrate only a one-percent benefit, due to limited idle times. As a result, most manufacturers are reluctant to invest in the technology.

DI Turbo with Ethanol

One of the downsides of corn-based ethanol is that current flex-fuel engines generally aren’t taking full advantage of E85’s 95- octane rating. But it’s easy to imagine a second-generation DI turbo engine that runs higher boost pressure when burning E85. Such an engine could be half the size of a current naturally aspirated powerplant, with substantially higher fuel economy. And when fueled with pure gasoline, the computer would simply dial back the boost. The engine would lose some power but without compromising durability or fuel efficiency.

A more radical way to harness ethanol’s higher octane rating is the “ethanol boosting system” (EBS). The concept is simple. Start with a DI-turbo engine and add a conventional port-fuel-injection system to it. Then add a second, small fuel tank and fill that one with E85. During modest loads, the engine runs on gasoline and port injection. But when you call for more power and the boost comes up, the DI system injects E85. Not only does E85 have a higher octane rating than gasoline, it also has more cooling effect. This allows safe operation above 20 psi of boost.

Ford has shown serious interest in the project. A twin-turbo 5.0-liter EBS engine might replace the 6.7-liter diesel in the Super Duty truck. It would develop the same power and torque, achieve similar fuel efficiency, and be cheaper to build because it doesn’t need any of the diesel’s expensive exhaust after-treatment.

In normal use, E85 consumption would be less than 10 percent of the gasoline consumption. Therefore, you save a lot of gas while consuming only a little ethanol. The EBS engine seems technically sound and has already survived preliminary tests.

(to be continued)

Notes:

challenge ['CxlInG] n. проблема

corn [kLn] n. зерно, кукуруза

dial back ["daIql 'bxk] v. отменять

feat [fJt] n. подвиг

flex-fuel engine ['fleksfjHql'enGIn] двигатель с гибким выбором топлива

innovation ["Inq'veISqn] n. нововведение

octane rating ['OkteIn'reItIN] октановое число

preliminary [prI'lImInqrI] adj. предварительный

pure [pjVq] adj. чистый

radical ['rxdIkql] adj. радикальный

reluctant [rI'lAktqnt] adj. не испытывающий желания

sturdy ['stWdI] adj. прочный

treatment ['trJtmqnt] n. обработка

zero ['zIqrqV] num. нуль

Ответьте на вопросы к тексту

1. What innovations of the internal combustion engine are described?

2. What is homogenous-charge compression ignition?

3. How does an HCCI engine work?

4. What’s the difference between a diesel engine and a HCCI one?

5. How can the HCCI mode be extended?

6. What are revised stop-start systems?

7. Why should they be developed?

8. How does Mazda’s i-stop system work?

9. Why are most manufacturers reluctant to invest in the technology?

10. What is a downside of corn-based ethanol?

11. How can a second-generation DI turbo engine solve the problem?

12. What is the concept of the EBS?

13. Why is Ford planning to use the system in its twin-turbo 5.0-liter EBS engine?

14. What does the EBS engine seem to be?

Лексические упражнения

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Урок 4.9

Текст А