The Clean Diesel Trifecta: Engine, Emissions, Fuel
The phrase clean diesel is tossed around with great abandon. One day it functions as the backbone for a car advertising campaign and the next it’s used to describe a specific technology, so if you’re confused you have lots of company.
Coined by the industry to herald a new generation of diesel power, the phrase strives to reinforce the message that diesel vehicles are as eco-friendly as their gas-based counterparts. To truly understand the essentials, however, it’s smart to focus on the clean diesel trifecta:
Advanced Engine Designs
Diesel engines are known for their power, but advanced engine designs have helped make diesels cleaner and quieter. The shape, depth and configuration of combustion chambers have been refined to optimize combustion, while turbochargers increase the amount of air so the fuel burns more completely, increasing efficiency and reducing particulates. Variable and high pressure fuel injectors adapt to different driving conditions and also offer a more complete burn, while electronic controls govern each function with great precision for peak performance and reduced emissions.
Enhanced Emissions Technologies
Carmakers have adopted varied approaches to reduce emissions and make diesels run cleaner. While some vehicles rely primarily on trappers and filters to capture particulates and prevent their release, others utilize a multi-stage selective catalytic reduction (SCR) process. It features a device similar to a catalytic converter that oxidizes hydrocarbons and carbon monoxide, coupled with an injector that adds a dose of diesel exhaust fluid (DEF). The urea-based solution creates a chemical reaction that converts harmful pollutants such as nitrogen oxides (NOx) into harmless compounds that can safely be exhausted as carbon, nitrogen and oxygen.
Clean diesel fuel, by definition, must contain 97% less sulfur than traditional diesel blends. Referred to as ultra-low sulfur diesel or ULSD, it was phased in to meet stricter air quality standards adopted in 2006. As of 2010, all diesel road vehicles shifted to ULSD and off-road equipment such as boats, construction, farm tractors and trains followed suit in 2012. ULSD provides the same engine power as earlier diesel blends and is roughly 30% more fuel efficient than gasoline, but the new formulation can reduce overall fuel mileage performance.
While specific technologies in each arena vary greatly by manufacturer, fuel remains the constant because the standards are defined and inflexible. The combined effects of the clean diesel trifecta have expanded diesel’s appeal and produced powerful, durable vehicles roughly 60 times cleaner than they were in the 1980s. As the search for completely clean diesel continues, these accomplishments are well worth noting.