Your Selections

Gopalakrishnan, Venkatesh
Show Only


File Formats

Content Types








   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

An Innovative Hybrid Powertrain for Small and Medium Boats

General Motors Global R & D-Venkatesh Gopalakrishnan, Michael Potter
General Motors LLC-Alok Warey
Published 2018-04-03 by SAE International in United States
Hybridization is a mainstream technology for automobiles, and its application is rapidly expanding in other fields. Marine propulsion is one such field that could benefit from electrification of the powertrain. In particular, for boats to sail in enclosed waterways, such as harbors, channels, lagoons, a pure electric mode would be highly desirable. The main challenge to accomplish hybridization is the additional weight of the electric components, in particular the batteries.The goal of this project is to replace a conventional 4-stroke turbocharged Diesel engine with a hybrid powertrain, without any penalty in terms of weight, overall dimensions, fuel efficiency, and pollutant emissions. This can be achieved by developing a new generation of 2-Stroke Diesel engines, and coupling them to a state-of-the art electric system. For the thermal units, two alternative designs without active valve train are considered: opposed piston and loop scavenged engines.The design of the alternative engines is carried out through CFD simulations. The CFD has been calibrated and validated using experimental data from single-cylinder loop scavenged engine.The study demonstrates that the new Loop scavenged…
This content contains downloadable datasets
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

Scavenge Ports Ooptimization of a 2-Stroke Opposed Piston Diesel Engine

General Motors Global R & D-Alok Warey
General Motors LLC-Michael Potter, Venkatesh Gopalakrishnan, Sandro Balestrino
Published 2017-09-04 by SAE International in United States
This work reports a CFD study on a 2-stroke (2-S) opposed piston high speed direct injection (HSDI) Diesel engine. The engine main features (bore, stroke, port timings, et cetera) are defined in a previous stage of the project, while the current analysis is focused on the assembly made up of scavenge ports, manifold and cylinder. The first step of the study consists in the construction of a parametric mesh on a simplified geometry. Two geometric parameters and three different operating conditions are considered. A CFD-3D simulation by using a customized version of the KIVA-4 code is performed on a set of 243 different cases, sweeping all the most interesting combinations of geometric parameters and operating conditions. The post-processing of this huge amount of data allow us to define the most effective geometric configuration, named baseline.In the second step of the study, the baseline is further optimized, keeping into account some fundamental design constraints, such as the overall dimensions of the manifold. The evolved geometry is then simulated by using KIVA, adopting a refined grid and…
This content contains downloadable datasets
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

An Analytical Assessment of the CO2 Emissions Benefit of Two-Stroke Diesel Engines

General Motors Research and Development-Alok Warey, Venkatesh Gopalakrishnan, Michael Potter
Universita di Modena e Reggio Emilia-Enrico Mattarelli, Carlo Alberto Rinaldini
Published 2016-04-05 by SAE International in United States
Two-stroke diesel engines could be a promising solution for reducing carbon dioxide (CO2) emissions from light-duty vehicles. The main objective of this study was to assess the potential of two-stroke engines in achieving a substantial reduction in CO2 emissions compared to four-stroke diesel baselines. As part of this study 1-D models were developed for loop scavenged two-stroke and opposed piston two-stroke diesel engine concepts.Based on the engine models and an in-house vehicle model, projections were made for the CO2 emissions for a representative light-duty vehicle over the New European Driving Cycle and the Worldwide Harmonized Light Vehicles Test Procedure. The loop scavenged two-stroke engine had about 5-6% lower CO2 emissions over the two driving cycles compared to a state of the art four-stroke diesel engine, while the opposed piston diesel engine had about 13-15% potential benefit. Opposed piston two-stroke engines offer the potential for even higher thermal efficiency than loop scavenged two-stroke engines. The efficiency advantages of the opposed piston two-stroke engine are mainly because of lower in-cylinder heat losses due to elimination of the…
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

Effect of High Levels of Boost and Recirculated Exhaust Gas on Diesel Combustion Characteristics at Part Load

General Motors Co.-Venkatesh Gopalakrishnan, Alberto Vassallo, Richard C. Peterson, Joaquin De la Morena
Published 2014-04-01 by SAE International in United States
Future diesel combustion systems may operate with significantly higher levels of boost and EGR than used with present systems. The potential benefits of higher boost and EGR were studied experimentally in a single-cylinder diesel engine with capability to adjust these parameters independently. The objective was to study the intake and exhaust conditions with a more optimum combustion phasing to minimize fuel consumption while maintaining proper constraints on emissions and combustion noise. The engine was tested at four part-load operating points using a Design of Experiments (DOE) approach. Two of the operating points correspond to low-speed and low-load conditions relevant for the New European Driving Cycle (NEDC). The other two points focus on medium load conditions representative of the World-wide harmonized Light-duty Test Procedures (WLTP). For the NEDC relevant conditions, improved fuel consumption was not achievable due to combustion noise constraints and the requirement for a very high turbocharger efficiency improvement of more than 20%. For the WLTP points, the Net Specific Fuel Consumption (NSFC) was improved by 11-12% with higher boost and EGR and improved…
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

Impact of Bore-to-Stroke Ratio Over Light-Duty DI Diesel Engine Performance, Emissions and Fuel Consumption: An Analytical Study Using 1D-CFD Coupled with DOE Methodology

General Motors Powertrain Europe Srl-Stefano Arrigoni, Roberto Cavallo, Riccardo Turcato, Alberto Racca
General Motors R&D-Alberto Vassallo, Venkatesh Gopalakrishnan
Published 2013-09-08 by SAE International in United States
It is traditionally accepted within the Diesel engine engineering community that Bore-to-stroke (B/S) ratios in the range ∼0.85 to ∼0.95 provide the best thermodynamic optimization for light-duty engines, mostly due to the favorable surface-to-volume ratio in the central phase of combustion, which reduces heat rejection, and to the torque-oriented volumetric efficiency profile. As a consequence, most engines into production exhibit B/S in that range, with few B/S ∼1.00 exceptions mainly for packaging issues on some V engines, and, very interestingly, on the last-generation of small and mid-sized engines.The analysis of the technical reasons behind this recent trend is performed in the present paper, by employing a 1D-CFD approach based on Design Of Experiment (DOE) methodology. A one-dimensional analysis was carried out using a detailed GT-Power model for a 1.6 liter light-duty Mid-sized Diesel Engine (MDE), characterized by best-in-class torque and power rating in its class. In addition to B/S ratio, the effects of compression ratio, boost pressure, exhaust restriction, peak cylinder pressure and exhaust temperature was studied, in order to grasp the mutual interrelations between…
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

Study of High Speed Gasoline Direct Injection Compression Ignition (GDICI) Engine Operation in the LTC Regime

SAE International Journal of Engines

General Motors LLC-Russ Durrett, Venkatesh Gopalakrishnan, Alejandro Plazas, Richard Peterson, Patrick Szymkowicz
Univ. of Wisconsin-Youngchul Ra, Rolf D. Reitz, Michael Andrie
  • Journal Article
  • 2011-01-1182
Published 2011-04-12 by SAE International in United States
An investigation of high speed direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline (termed GDICI for Gasoline Direct-Injection Compression Ignition) in the low temperature combustion (LTC) regime is presented. As an aid to plan engine experiments at full load (16 bar IMEP, 2500 rev/min), exploration of operating conditions was first performed numerically employing a multi-dimensional CFD code, KIVA-ERC-Chemkin, that features improved sub-models and the Chemkin library. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. Operation ranges of a light-duty diesel engine operating with GDICI combustion with constraints of combustion efficiency, noise level (pressure rise rate) and emissions were identified as functions of injection timings, exhaust gas recirculation rate and the fuel split ratio of double-pulse injections. Parametric variation of the operation ranges was also investigated with respect to initial gas temperature, boost pressure and injection pressure. Following the modeling, experiments were performed under the conditions suggested by the numerical results in order to confirm the feasibility of GDICI operation at full load, as…
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

An Investigation of Ignition and Heat Release Characteristics in a Diesel Engine Using an Interactive Flamelet Model

School of Mechanical Engineering, Purdue University-Venkatesh Gopalakrishnan, John Abraham
Published 2003-03-03 by SAE International in United States
A multidimensional model is employed to model ignition and heat release rates in a Diesel engine. An interactive flamelet model is employed to model combustion. Nheptane is used as a representative fuel for Diesel fuel in the computations. Comparisons of computed and measured results are presented for a range of engine operating conditions: speed 1200 rpm, start of injection 12.5 degrees before top dead center to 9.5 degrees after top dead center and intake air temperature of 340-360 K. The primary objective of this work is to assess the ability of the model to reproduce ignition timings. The flamelet model uses detailed chemical kinetics and it is shown that it can reproduce the qualitative trends of changes in ignition delay and heat release rates with respect to changes in operating conditions of the engine. The capability to reproduce the measured changes in ignition delay is important because changes in injection timing lead to changes in ignition timing. Changes in ignition timing, coupled with changes in injection pressure and EGR, are employed to control NO and…
Annotation ability available
   This content is not included in your SAE MOBILUS subscription, or you are not logged in.

A Mixture Fraction Averaged Approach to Modeling NO and Soot in Diesel Engines

Purdue University-Amrita R. Wadhwa, Venkatesh Gopalakrishnan, John Abraham
Published 2001-03-05 by SAE International in United States
Multidimensional models are increasingly employed to predict NO and soot emissions from Diesel engines. In the traditional approach, the ensemble-averaged values of variables are employed in the expressions for NO and soot formation and oxidation. In the mixture fraction averaged approach, the values of state variables and species concentrations are obtained from the structure of laminar diffusion flames. The source terms for NO and soot are then obtained by averaging across the mixture fraction coordinate with a probability density function. The clipped-Gaussian probability density function and profiles obtained by employing the OPPDIF code (part of the CHEMKIN package) for the laminar flame structure are employed in this work. The Zeldovich mechanism for NO formation and the Moss et al. formation and Nagle-Strickland-Constable oxidation model for soot have been employed to study the qualitative trends of pollutants in transient combusting Diesel jets. Computations are carried out in an axisymmetric constant volume chamber to evaluate the approach. It is shown that the computed NO and soot behavior and the jet flowfield structure are consistent with experimental findings.
Annotation ability available