Efficacy Of Heated Hydrous Ethanol Injection For Improving Emissions From Dual Fuel Diesel Engines

Abstract

With emissions standards becoming ever more stringent, aftermarket dual-fuel solutions are being developed to allow legacy diesel engines to reach higher regulatory emissions tiers. Manufacturers are reluctant to adopt dual-fuel systems due to perceived lack of consumer interest. However, the use of aftermarket dual-fuel systems with partially renewable fuels has sparked interest in limited markets. Previous research has shown slight emissions reduction benefits from fumigation with 120 proof hydrous ethanol in a diesel engine using a commercially available dual-fuel system. However, the findings do not match manufacturer claims of emissions reductions. The work presented here examines the design, development, performance, and emissions from an engine equipped with a novel aftermarket port fuel injection (PFI) dual fuel system with a fuel heating system integrated into the fuel injector rail. Finite element modeling techniques in ANSYS were used to optimize the heat exchanger and analyze its performance. In addition, cross-sections and flow path lines were created in ANSYS to examine thermal profiles and flow turbulence at varying ethanol flow rates. A John Deere 4045HF475 Tier 2 diesel engine was retrofitted with a custom PFI rail designed to inject hydrous ethanol with the ability to preheat the ethanol using circulated hot engine coolant to improve the vaporization and mixing of the secondary fuel and air in the intake port. Port-injected fuel flow was controlled by varying injector pulse width and throttle position was adjusted manually to maintain testing mode parameters. Heated ethanol, unheated ethanol, and diesel only operating modes were run over a modified ISO 8178 eight-point test plan. Fumigant energy fraction (FEF), defined as the amount of energy provided by the fumigant based on the lower heating value (LHV) divided by the total fuel energy, up to 37% was achieved in the experiments. Ethanol fuel rail heat exchanger effectiveness decreased with increasing FEF and log-mean temperature difference (LMTD) increased. These opposite effects were likely due to dimensional design constraints of the heat exchanger limiting the heat transfer. Experiments found that with increasing FEF, engine NO emissions decreased, whereas NO2, CO, THC, and ethanol emissions increased. NO emissions reductions were countered by increasing NO2, resulting in constant NOX emissions. Soot concentrations produced varying trends, but with a tendency to decrease overall at high FEF. Preheating the ethanol with circulated engine coolant yielded few benefits to engine out-emissions. This study showed that the dual-fuel heated PFI rail system provided modest emissions benefits over diesel-only operation. Preheating the liquid ethanol was not as successful as anticipated because ethanol’s high latent heat of vaporization dominated over the sensible heat required to heat the liquid prior to the injectors.