Hydrous Ethanol Steam Reforming and Thermochemical Recuperation to Improve Dual-Fuel Diesel Engine Emissions and Efficiency

Abstract

Dual-fuel strategies can enable replacement of diesel fuel with low reactivity biofuels like hydrous ethanol. Previous work has shown that dual-fuel strategies using port injection of hydrous ethanol can replace up to 60% of diesel fuel on an energy basis. However, they yield negligible benefits in NOX emissions, soot emissions, and brake thermal efficiency (BTE) over conventional single fuel diesel operation. Pretreatment of hydrous ethanol through steam reforming before mixing with intake air offers the potential to both increase BTE and decrease soot and NOX emissions. Steam reforming can upgrade the heating value of the secondary fuel through thermochemical recuperation (TCR) and produces inert gases to act as a diluent similar to exhaust gas recirculation. This study experimentally investigated a novel thermally integrated steam reforming TCR reactor that uses sensible and chemical energy in the exhaust to provide the necessary heat for hydrous ethanol steam reforming. An off-highway diesel engine was operated at three speed and load settings with varying hydrous ethanol flow rates reaching fumigant energy fractions of up to 70%. The engine achieved soot reductions of close to 90% and minor NOX reductions; however, carbon monoxide and unburned hydrocarbon emissions increased. A first law energy balance using the experimental data shows that the developed TCR system effectively upgraded the heating value of the secondary fuel. Overall, hydrous ethanol steam reforming using TCR can lead to 23% increase in fuel heating value at 100% conversion, a limit approached in the conducted experiments.

Thermochemical Recuperation to Enable Efficient Ammonia-Diesel Dual-Fuel Combustion in a Compression Ignition Engine

“…Ammonia dual-fuel operation resulted in a sharp decrease in combustion efficiency for all modes, with the most significant decline seen for lower-load modes. Reasons for poor combustion efficiency include positive valve overlap in the tested engine, as has been discussed in our earlier work [44], as well as cold areas of the combustion chamber as in the squish volume, as has been discussed in other dual-fuel engine studies [54,55]. Combustion efficiency declines were mitigated for the increased hydrogen mole fraction in the intake, as can be seen by comparing the bottom and top panels of Figure 5.…”

“…In that work, soot and NO x were both decreased to near-zero levels, at the expense of fuel consumption. In a later study, the same group [44] demonstrated both thermochemical recuperation and emissions reductions using ethanol steam reforming in a diesel-ethanol dual-fuel mode. For ammonia, Wang et al [13] explored the feasibility of an autothermal ammonia decomposition (ATD) system for diesel engines.…”

Improving Thermal Efficiency of Internal Combustion Engines: Recent Progress and Remaining Challenges

“…Dry reforming (with carbon dioxide) can provide the best recuperation, but it is vulnerable to rapid coking. Recently, Hwang et al [290] experimentally studied a "novel thermally incorporated steam reforming TCR reactor, which utilizes sensible and chemical energy in the exhaust to afford the required heat for hydrous ethanol steam reforming. Off-highway diesel engines were run at three different speeds and loads with diverging hydrous ethanol flow rates arriving fumigated energy fractions of up to 70%".…”