Prathik Meruva’s research while affiliated with Southwest Research Institute and other places

div class="section abstract"> Battery electric vehicles (BEVs) are well-suited for many passenger vehicle applications, but high cost, short range, and long recharging times have limited their growth in commercial vehicle markets. These constraints can be eliminated with plug-in hybrid electric vehicles (PHEVs) which combine many benefits of BEVs with those of conventional vehicles. In this study, research was conducted to determine the optimal hybrid electric powertrain system for a Class 3, light duty commercial vehicle. The key technologies used in this hybrid powertrain include engine downsizing, P3 architecture hybridization, and active thermal management of aftertreatment. A vehicle cost of ownership analysis was conducted to determine the economic viability, a very important consideration for commercial vehicles. Several combinations of E-motor and battery pack sizes were evaluated during the cost analysis and the best possible configuration was determined. The resulting vehicle powertrain demonstrated ~60% reduction in CO₂ over the World Harmonized Light Duty Transient Cycle (WLTC) and Federal Transient Procedure (FTP75) test cycles compared to the baseline internal combustion engine (ICE) vehicle. The NO_X emissions were also evaluated during those test cycles, and the test results indicated that intermittent engine operation associated with Plug-in Hybrid Electric Vehicle (PHEV) operation, can result in higher NO_X emissions. Advanced aftertreatment thermal management strategies are required to reduce NO_X emissions in PHEVs. Finally, an exhaust heater was used to reduce tailpipe (TP) NO_X emissions, and a pathway for even lower NO_X emissions is identified. </div

div class="section abstract"> In this study, engine-out gaseous emissions are reviewed using the Fourier Transform Infrared (FTIR) spectroscopy measurement of methanol diesel dual fuel combustion experiments performed in a heavy-duty diesel engine. Comparison to the baseline diesel-only condition shows that methanol-diesel dual fuel combustion leads to higher regulated carbon monoxide (CO) emissions and unburned hydrocarbons (UHC). However, NO_X emissions were reduced effectively with increasing methanol substitution rate (MSR). Under dual-fuel operation with methanol, emissions of nitrogen oxides (NO_X), including nitric oxide (NO), nitrogen dioxide (NO₂), and nitrous oxide (N₂O), indicate the potential to reduce the burden of NO_X on diesel after-treatment devices such as selective catalytic reduction (SCR). Other unregulated gaseous emissions, such as formaldehyde (CH₂O) methane (CH₄), increased with higher MSR, but their emissions can be mitigated if advanced injection timing or increased intake temperature is used as reported in our separate study. In summary, this study suggests the potential use of methanol as a low-carbon fuel (LCF) to meet emissions regulations but indicates a slight increase in emissions of unregulated species. </div

div>Commercial vehicles require advanced engine and aftertreatment (AT) systems to meet upcoming nitrogen oxides (NO_x) and carbon dioxide (CO₂) regulations. This article focuses on the development and calibration of a model-based controller (MBC) for an advanced diesel AT system. The MBC was first applied to a standard AT system including a diesel particulate filter (DPF) and selective catalytic reduction (SCR) catalyst. Next, a light-off SCR (LO-SCR) was added upstream of the standard AT system. The MBC was optimized for both catalysts for a production engine where the diesel exhaust fluid (DEF) was unheated for both SCRs. This research shows that the tailpipe (TP) NO_x could be reduced by using MBC on both catalysts. The net result was increased NO_x conversion efficiency by one percentage point on both the LO-SCR and the primary SCR. The CO₂ emissions were slightly reduced, but this effect was not significant. Finally, the MBC was used with a final setup representative of future AT systems which included standard insulation on the catalysts and optimal DEF dosing controls. This final configuration resulted in an improved NO_x and CO₂ such that the composite Federal Test Procedure (FTP) NO_x was 0.060 g/hp-hr and the composite FTP CO₂ was 508.5 g/hp-hr. The article details this cycle along with the low-load cycle (LLC) and beverage cycle. More technologies are required to meet the future California Air Resources Board (CARB) 2027 standard, which will be shown in future work.</div

Meeting regulatory and customer demands requires detailed powertrain calibration which can be expensive and time-consuming. There is often a reliance on mathematical optimization tools to convert experimental learnings into a final calibration. This work focuses on developing multiple neural network machine learning (ML) models which were trained on different test-train data splits of test-cell recorded steady-state medium-duty (MD) diesel engine data. The output data was used to develop engine actuator maps by utilizing a genetic algorithm (GA). The genetic algorithm contains a fitness function which was varied to target different combinations of low NOx and CO2 emissions. The input variables used for the ML model were engine speed, engine torque, fuel rail pressure, exhaust gas recirculation (EGR) valve command, main injection timing, and wastegate valve command. The output variables predicted were NOx mass flow rate, exhaust temperature, fuel flow rate, and dry intake mass flow rate. The ML models were used to predict cycle-averaged engine-out emissions and time-series predictions of all output variables for different transient drive cycles. The drive cycles used for this case were the Heavy-Duty Federal Test Procedure (HDFTP) transient cycle, the Non-Road Transient Cycle (NRTC), the Ramped Mode Cycle (RMC) and the newly proposed on-road Low-Load Cycle (LLC).

New regulations by the California Air Resources Board (CARB) demand a stringent 0.02 g/hp-hr tailpipe NO x limit by the year 2027, requiring Selective Catalytic Reduction (SCR) catalysts to provide high NO x conversions even at low (below 200°C) exhaust temperatures. This work describes utilizing an Electrically Heated Mixer System (EHM system) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) catalyst followed by a conventional aftertreatment (AT) system containing DOC, DPF, and SCR, enabling high NO x conversions meeting CARB’s NO x emission target. The AT catalysts were hydrothermally aged to Full Useful Life. Conventional unheated Diesel Exhaust Fluid (DEF) was injected upstream of both the LO-SCR and primary downstream SCR. The EHM system allowed for DEF to be injected as low as 130°C upstream of the LO-SCR, whereas, in previous studies, unheated DEF was injected at 180°C or dosed at 130°C with heated DEF. The combination of unheated DEF, EHM system, LO-SCR, and downstream SCR enabled the needed increase in NO x efficiency in low exhaust temperatures, which was observed in drive cycles such as in cold-FTP, LLC, and World Harmonized Transient Cycle (WHTC). There were several-fold reductions in tailpipe NO x using this configuration compared to its baseline: 3.3-fold reduction in FTP, 22-fold in Low Load Cycle (LLC), 38-fold in Beverage Cycle, 8-fold in “Stay Hot” Cycle, and 10-fold in WHTC. Finally, it is shown that the EHM system can heat the exhaust gas, such as during a cold start, without needing additional heating hardware integrated into the system. These results were observed without performing changes in the engine base calibration.

Engine and aftertreatment solutions are being identified to meet the upcoming ultra-low NO x regulations on heavy duty vehicles as published by the California Air Resources Board (CARB) and proposed by the United States Environmental Protection Agency (US EPA) for the year 2027 and beyond. These standards will require changes to current conventional aftertreatment systems for dealing with low exhaust temperature scenarios. One approach to meeting this challenge is to supply additional heat from the engine; however, this comes with a fuel penalty which is not attractive and encourages other options. Another method is to supply external generated heat directly to the aftertreatment system. The following work focuses on the later approach by maintaining the production engine calibration and coupling this with an Electric Heater (EH) upstream of a Light-Off Selective Catalytic Reduction (LO-SCR) followed by a primary aftertreatment system containing a downstream Selective Catalytic Reduction (SCR). External heat is supplied to the aftertreatment system using an EH to reduce the Tailpipe (TP) NO x emissions with minimal fuel penalty. Two configurations have been implemented, the first is a Close Coupled (CC) LO-SCR configuration and the second is an Underfloor (UF) LO-SCR configuration. The CC LO-SCR configuration shows the best outcome as it is closer to the engine, helping it achieve the required temperature with lower EH power while the UF LO-SCR configurations addresses the real-world packaging options for the LO-SCR. This work shows that a 7 kW EH upstream of a LO-SCR, in the absence of heated Diesel Exhaust Fluid (DEF), followed by a primary aftertreatment system met the 2027 NO x regulatory limit. It also shows that the sub-6-inch diameter EH with negligible pressure drop can be easily packaged into the future aftertreatment system.