Honda’s 2.2 i-CTD four-cylinder diesel engine already is available in Europe, but the company knows it’s not clean enough to meet the EPA’s Tier 2 Bin 5 emissions requirements. Adding a technology like DaimlerChrysler’s BLUETEC urea injection (Diesel Goes Blue), is one option, but it requires that the vehicle operator replenish the urea tank. To take the operator out of the loop, Honda engineers created a NOx catalyst that generates its own ammonia to turn NOx into nitrogen.
The catalyst has two layers, with the first adsorbing NOx and converting part of it into ammonia. In the second layer, ammonia is adsorbed and used to convert the remaining NOx in the exhaust into nitrogen. This catalyst sits downstream of the combined oxidation catalyst and diesel particulate filter, and features enhanced NOx reduction in the 200°C to 300°C temperature range most diesels operate within. In addition, Honda optimized the combustion chamber design, added a 2,000-bar common-rail injection system with piezo-electric injectors, and boosted the efficiency of the EGR system. Work remains in meeting U.S. on-board diagnostic requirements and handling fuels with varying cetane numbers, but Honda plans to have the engine available in the U.S. market by 2009.
It has taken years to develop, but Subaru has finally launched its horizontally opposed four diesel engine. Subaru prefers the boxer layout as it keeps the engine’s center of gravity low, its dimensions compact, and lessens driveline inclination. (The latter is important with all-wheel-drive.) However, this layout also makes it more difficult to control the vibration that comes from compression ignition, which affects refinement. Use of high-pressure (2,000 bar) common-rail direct injection with multiple injections per revolution are used to quell the vibration while reducing the engine’s NOx output. The engine also features graphite coating on the piston skirts to reduce friction, four valves per cylinder, and a single turbocharger with intercooler.