Mitsubishi Motors is determined to play its part in the reduction of carbon dioxide emissions (CO₂), considered to be a vital factor in preserving the environment on a global scale. To this end, the company has positioned the GDI engine as its standard engine family and is focused on extending its installation to all Mitsubishi gasoline passenger cars. Cumulative production of GDI engines topped 200,000 units in February this year. Mitsubishi's GDI eco-friendly engines achieve significant reductions in fuel consumption and CO₂ emissions, while at the same time generating higher power outputs over the company's port injection engines.

To consolidate the GDI engine's status as the definitive eco-friendly power unit, the company has taken a fresh look at the combustion process with the aim of reducing emission levels further still. This research has enabled the company to further evolve its world-leading GDI technology to a stage that realizes a greater than 80 percent reduction in current regulated levels for carbon monoxide (CO), hydrocarbons (HC), oxides of nitrogen (NOx) and other toxic substances, without any dilution of the original benefits stemming from GDI technology. The company plans to market in Japan this autumn a low-emission automobile incorporating the new technology that will meet the more stringent emission levels recommended in the November 1997 Japanese Central Environment Council report for introduction in Japan in the year 2000.

The new GDI engine is a true Global Standard Eco-engine for it is able to rationally integrate the individual new technologies in a manner that best matches different conditions in different markets and thus meet future environmental requirements the world over. Mitsubishi Motors is soon to start marketing vehicles powered by Global Standard Eco-engines in the United States and its other world markets.

1. Mitsubishi Motors approach to global environment

(1) Reduction of CO₂ emissions

The reduction of CO₂ emissions is an issue of global importance and must be considered in terms of the total life cycle of a vehicle, this including the manufacturing process and not just use of the vehicle on the road. Furthermore, because total emission quantities are proportional to the number of vehicles on the road, emission reducing technology must be applicable to as many vehicles as possible.

Because the GDI engine requires no major changes in the manufacturing process, there is no increase in CO₂ emissions while the engine is being made. Consequently, reductions in fuel consumption translate directly into reductions in CO₂ emissions. In addition, because it be produced at a cost very similar to that of a conventional engine, the GDI engine has the potential for becoming the manufacturer's standard power unit and represents the best choice among all the candidate technologies currently available.

Mitsubishi Motors has positioned the GDI engine as its core technology for reducing CO₂ emissions. The GDI family of Eco-engines first took to the road powering the new GALANT series launched in August 1996 and since then the company has introduced GDI-powered models in several of its passenger car series, the latest being the RVR sport-utility in November 1997. Cumulative GDI engine production topped 200,000 units in the early part of February 1998.

The company plans to use the GDI engine to power 85 percent of all its gasoline passenger cars (minicars excluded) in Japan by 2000, and 100 percent by 2010. As a result, the level of CO₂ emissions from Mitsubishi gasoline passenger cars sold in the year 2005 will be 20 percent less per vehicle than in 1995.

(2) Reductions of CO, HC and NOx emissions

Exhaust gas purification, as represented by reductions of CO, HC and NOx levels, is an area of major importance in terms of conserving the urban environment. More stringent emission levels are being proposed in many nations, with Japan currently preparing to introduce the world's toughest NOx levels in the year 2000.

Mitsubishi Motors has developed a new GDI engine technology that reduces current regulated HC and NOx levels by 80 percent, without diluting the benefits of the original GDI engine technology. The company plans to introduce this autumn a model on the Japanese market that is powered using the new technology, and then extend application of the technology to other models in the company lineup.

The company also plans to introduce on its world markets models that incorporate the new GDI technology and the newly-developed exhaust purification technology, which takes into account both proposed changes in regulations and different fuel situations in countries around the world.

In Europe, the company launched the GDI CARISMA passenger model in October 1997. At the beginning of 1999, the company will launch a low-pollution model that meets European emission levels due to come into force in 2000. This will be followed by the introduction of other emission standard models.

In the United States, the company plans to introduce a GDI-powered model that conforms to California's Ultra-low Emission Vehicle standards in the autumn of 1999. This will be followed by the introduction of other emission standard models.

*1 All levels are for the Japanese 10-15 mode urban driving cycle.
*2 GALANT class model with 6,400km age exhaust system, measured at MMC laboratories
*3 As recommended in November 21, 1997 report by the Japanese Central Environment Council

2. GDI exhaust purification technology

Exhaust emission regulations exist to govern levels of the CO, HC and NOx emissions that are so important in terms of local air quality. Advances in engine management technology have made it a relatively simple matter to reduce CO emissions, and efforts are currently being focused on the purification of HC and NOx emissions.

Reducing HC and NOx emissions is not a simple task in the direct injection engine and there has been concern in some quarters about whether this technology would be able to cope with the increasingly stringent emission levels forecast around the world.

Mitsubishi Motors has found that it is possible to reduce HC and NOx levels by using new technologies that enable the GDI engine combustion mode to be controlled as required. The HC and NOx purification technologies include: (1) Two-stage combustion, which utilizes the free control of mixture formation that is unique to the GDI engine; (2) A reactive exhaust manifold, which further boosts the effectiveness of two-stage combustion; (3) High volume exhaust gas recirculation that is enabled by the stable combustion inherent to GDI technology; (4) Improved lean NOx catalysts (LNC).

The important point about emission regulations is that level priorities for individual emission components, driving modes and gasoline properties vary from country to country. The point about Mitsubishi Motors' new GDI technology is that its component technologies can be tailored and adapted to suit individual circumstances in different countries.

(1) HC reduction technology

The three-way catalytic converter used with gasoline engines operates to remove HCs from engine-out emissions only when the catalyst temperature rises above 250 degrees centigrade. Bringing the converter up to operating temperature in as short a time as possible immediately after a cold-start is therefore a major key in the reduction of HC emissions.

Helping to make this a reality is Mitsubishi's new GDI two-stage combustion mode technology in which fuel is injected twice during a single cycle ? at the end of the compression stroke and in the latter stage of the expansion stroke. This is complemented by the use of a reactive exhaust manifold.

Conventional converters typically take more than 100 seconds to reach a temperature of 250 degrees centigrade. Two-stage combustion technology cuts this time in half, and the use of a reactive exhaust manifold brings the time down to around 20 seconds. The reactive manifold momentarily detains exhaust gases, promoting their oxidation and allowing the combustion reaction started in the combustion chamber to continue in the exhaust manifold. The result is a major reduction in cold-start HC emissions.

(2) NOx reduction technology

Three-way catalytic converters are highly effective in removing HC and NOx (NOx) from engine-out emissions in engines burning stoichiometric air/fuel mixtures. The GDI engine is an ultra-leanburn engine, however, and so the use of such converters is not an option, requiring instead a lean NOx catalytic converter (LNC) that operates effectively under ultra-lean conditions. There are two types of LNC: the selective reduction type and the NOx trap type.

While the converter is new, the NOx trap removes NOx more efficiently. However, its performance deteriorates rapidly with certain types of gasoline. Meanwhile, the selective reduction catalyst, although less efficient initially, is unaffected by the type of gasoline. Mitsubishi Motors intends to exploit these characteristics and use the catalyst type best suited to a particular market.

• Selective reduction LNC: Europe and other markets where fuel conditions are less favorable.
• NOx trap LNC: Japan, California and other markets where fuel conditions are favorable.