New Diesel Engine Concept Regulates Heat to Reduce Emissions

Featuring a design that has not changed much in half a century, diesel engines are still the undisputed combustion concepts used today. However, what has changed is the intricacy of the systems surrounding the diesel engine block to overcome intrinsic inefficiencies in emissions.

Just recently, a research team at the New ACE Institute in Japan has developed a new diesel combustion engine concept utilizing several fuel injectors that do not need waste heat reduction. With a brake thermal efficiency greater than 50 percent, the new engine is claimed to reduce engine manufacture costs.

Waste heat recovery (WHR) is typically used as a method of capturing the heat of the engine to maintain a temperature in a particulate filter and other emissions control systems. While it is true that WHR is expensive, it helps the vehicle’s overall efficiencies in both emissions reductions and fuel use. The team of automotive researchers at New ACE found a way to enhance combustion that overcomes the intricate tradeoffs between brake thermal efficiency (BTE), emissions, and energy losses on traditional diesel combustion.

The team’s engine uses three fuel injectors in a variant of the Sabathe cycle. This limited pressure, dual cycle regulates heat by holding constant volume and pressure in the cylinder. Modified, this new concept can now regulate fuel injection to temporarily create an isolation between the premixed combustion area and diffusion combustion area of the cylinder, which enables consecutive heat release.

This is achieved by fitting three injectors to the cylinder. One is vertically mounted at the center and two more are positioned at an angle on either flank at the piston cavity’s circumference. With the side-angled sprays directed along the swirl direction of the airflow, this enhances mixing and prevents spray interference and impingement on the cavity wall, thus creating a denser combustion point. Shaping of the piston cavity also helps inhibit injection interference between injectors.

By regulating injection timing and duration under constant fuel pressure, heat can be controlled at various operating temperatures and compression ratios. The center injector fires first, followed by precision timing of the side injectors.

Experimental results for the engine concept revealed that friction and heat losses were reduced. This created lower smoke and NOx emissions when compared to traditional diesel combustion.

The New ACE Institute intends to further develop this engine concept.