|Honda’s 4-stroke test-bed
The Wall Street Journal reported this week that Honda may introduce an HCCI-type engine in a hybrid application that could result in a new Civic hybrid achieving as much as 65 mpg—30% better than the new 2006 version.
According to the engineers who spoke to the WSJ on the condition of anonymity, the company is ready to reveal its R&D results and show a prototype four-cylinder HCCI engine as early as next year.
HCCI—Homogeneous Charge Compression Ignition—relies upon a very lean (high proportion of air to fuel) and well-mixed (Homogeneous) air-fuel mixture (Charge) that is compressed (Compression) until it autoignites (Ignition). (The HCCI approach is also called Controlled Auto-Ignition: CAI.)
The resulting spontaneous burn produces a flameless energy release in a large zone almost simultaneously—very different than the spark/gasoline burn or the compression/diesel burn. (Earlier post.)
HCCI combustion can deliver a very efficient engine, potentially providing a 20% to 30% boost in gasoline engine efficiency without the nasty NOx or PM emissions of a diesel. Theoretically it can operate using a variety of fuels: gasoline, diesel, natural gas, biofuels, or hydrogen. Used in a hybrid application, the more efficient engine would increase the overall fuel efficiency of the powertrain.
Managing the combustion for the different types of fuels, though, is extremely tricky, and is the subject of a large amount of R&D. Most recently, GM announced it is working with supplier Robert Bosch and Stanford University to accelerate development of HCCI engines with a three-year, $2.5-million research program. (Earlier post.)
To develop more efficient gasoline engines, Honda opened an Advanced Powertrain Research center in Japan to focus on improving internal-combustion technology. The goal is to deliver a gasoline engine with a thermal efficiency between 40% to 50% through a combination of different technologies such as HCCI. Reaching that level of thermal efficiency would more than double the present efficiency of a typical gasoline engine.
The company has been working on auto-ignition schemes, which it termed Activated Radical Combustion, in two-stroke engines for its motorcycles, for a number of years.
According to the engineers cited in the Journal piece, Honda has been able to clear obstacles to create a prototype four-cylinder HCCI engine that runs smoothly in a low-to-medium speed range.
That, they said, should represent about 65% of the load range necessary to run a gasoline engine properly on the highway. The main challenge left to clear is high speeds, or above 4,000 revolutions per minute, the engineers said. A typical Honda gasoline-fueled engine covers a range reaching 6,000 RPMs.
In 2004, when discussing the potential of its HCCI work, Honda CEO Takeo Fukui estimated that an HCCI Accord could get 50 mpg (double that of conventional Accords) and that a HCCI hybrid Accord could boost mileage to 70 mpg.
Experimental Studies on the Auto-ignition Combustion for the Petrol Engines; Yoichi Ishibashi, Honda R&D