# Hybrid-Electric Vehicle with Natural Gas-Diesel Engine

^{*}

## Abstract

**:**

## 1. Introduction

#### 1.1. Carbon Dioxide Emissions of a Vehicle

#### 1.2. Required Fuel Energy of a Vehicle

#### 1.3. Influence of Hybridization

#### 1.4. Dual-Fuel Natural Gas-Diesel Engine

#### 1.5. Contribution

#### 1.6. Outline

- In Section 2, the materials and methods used are described, including details on the engine test bench, information on engine control, a description of the measurement devices installed and of calculations based on the measurement results as well as details on hardware-in-the-loop experiments and a description of the component models used.
- Section 3 contains the results, including those of static engine measurements of the natural gas-Diesel engine and of the vehicle emulation results.
- In Section 4, a summary is given and conclusions are drawn.

## 2. Materials and Methods

#### 2.1. Engine Test Bench

- port-fuel injection system for gaseous fuels;
- low-pressure exhaust gas recirculation system; and
- cylinder-pressure sensors in all four cylinders.

Engine Type | Volkswagen TDI 2.0-475 NE (CJDA), industrial engine |

Cylinders | 4 |

Displ. Volume | 1.968 L |

Bore | 81.0 mm |

Stroke | 95.5 mm |

Compression Ratio | 16.5 |

Injection System | Bosch common rail with piezo injectors |

#### 2.2. Engine Control

#### 2.3. Measurements and Calculations

#### 2.3.1. Measurements

- Engine torque is measured with an in-line torque transducer “Vibrometer TG20BP” with a nominal torque of 200 $\mathrm{N}\mathrm{m}$ and a maximum measurement torque of 400 $\mathrm{N}\mathrm{m}$;
- Engine speed is measured with an incremental angular encoder “Haidenhein ROD 426” with 1800 pulses. The encoder is connected to the crankshaft of the engine;
- Diesel consumption is measured with a scale “Mettler Toledo MS 6002S/01” with a resolution of $0.01\phantom{\rule{0.166667em}{0ex}}g$. The Diesel consumption is the difference of the weight of the Diesel tank between the start and the end of the measurement;
- Gas consumption is measured with a coriolis mass flow meter “Rheonik RHM015”. Its signal conditioning unit generates a pulse every $0.1\phantom{\rule{0.166667em}{0ex}}g$. Total gas consumption is obtained by summing up these pulses. Total gas consumption is additionally measured with another scale “Mettler Toledo MS 32001L/01” with a resolution of $0.1\phantom{\rule{0.166667em}{0ex}}g$. The consumption is the difference of the weight of the gas bottle between the start and the end of the measurement;
- Nitrogen oxide emissions are measured with a “Continental Smart NO${}_{x}$ Sensor”, and with a “Cambustion fNOx 400”;
- Air-fuel ratio is also measured with the same “Continental Smart NO${}_{x}$ Sensor”;
- Soot is measured with an “AVL Micro Soot Sensor”.

#### 2.3.2. Calculations

- Engine Efficiency is calculated based on the following Equation:$${\eta}_{\mathrm{ICE}}=\frac{{\int}_{\mathrm{Injection}\mathrm{On}}\left({T}_{ICE}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{\omega}_{ICE}\right)\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}dt}{{m}_{D}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}H{l}_{D}+{m}_{G}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}H{l}_{G}}$$
**Table 2.**Fuel Properties.Parameter Diesel Methane Natural Gas Lower heating value (MJ/kg) 43.1 50.02 46.11 Mass $C{O}_{2}$ emitted per mass of fuel burnt (-) 3.16 2.74 2.61 - Gas Ratio is the energetic gas ratio with respect to the total fuel energy. The ratio is calculated based on the following Equation:$${r}_{\mathrm{G}}=\frac{{m}_{G}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}H{l}_{G}}{{m}_{G}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}H{l}_{G}+{m}_{D}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}H{l}_{D}}$$
- Nitrogen oxide emissions are measured in parts per million. To convert that value to gram per kilowatt hour, the following assumptions are made:
- -
- NO${}_{x}$ only consists of NO;
- -
- Diesel is represented by ${C}_{8}{H}_{18}$; and
- -
- Air consists of 21% ${O}_{2}$ and 79% ${N}_{2}$.

$$({n}_{G}+8{n}_{D})\phantom{\rule{4pt}{0ex}}C{O}_{2}+(2{n}_{G}+9{n}_{D})\phantom{\rule{4pt}{0ex}}{H}_{2}O+(2{n}_{G}+12.5{n}_{D})\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\left(\lambda \phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}3.76\phantom{\rule{4pt}{0ex}}{N}_{2}+(\lambda -1)\phantom{\rule{4pt}{0ex}}{O}_{2}\right)$$$$N{O}_{x}[g/kWh]=\phantom{\rule{4pt}{0ex}}\frac{\frac{{m}_{G}}{{M}_{C{H}_{4}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\left(9.5\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\lambda +1\right)+\frac{{m}_{D}}{{M}_{{C}_{8}{H}_{18}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\left(59.5\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\lambda +4.5\right)}{\int {T}_{ICE}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{\omega}_{ICE}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}dt\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\frac{1}{3600\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{10}^{3}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{M}_{NO}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\frac{N{O}_{x}\left[ppm\right]}{{10}^{6}}$$ - Soot is measured in milligram per cubic meter with respect to standard temperature and pressure. The conversion to milligram per kilowatt hour is similar to the conversion of the nitrogen oxide emissions:$$Soot\phantom{\rule{4pt}{0ex}}[mg/kWh]=\phantom{\rule{4pt}{0ex}}\frac{\frac{{m}_{G}}{{M}_{C{H}_{4}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\left(9.5\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\lambda +1\right)+\frac{{m}_{D}}{{M}_{{C}_{8}{H}_{18}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\left(59.5\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\lambda +4.5\right)}{\int {T}_{ICE}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{\omega}_{ICE}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}dt\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\frac{1}{3600\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{10}^{3}}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}\frac{R\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{T}_{STP}}{{p}_{STP}}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}Soot\phantom{\rule{4pt}{0ex}}[mg/{m}^{3}]$$
- Carbon dioxide emissions are calculated based on the measured fuel consumption:$${m}_{{\text{CO}}_{2}}={\nu}_{D}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{m}_{D}+{\nu}_{G}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{m}_{G}$$

#### 2.4. Vehicle Emulation (Hardware-in-the-Loop Experiments)

#### 2.4.1. Powertrains Investigated

**Figure 3.**Powertrains investigated: Conventional (non-hybrid) vehicle on the left-hand side. Hybrid-electric vehicle on the right-hand side.

#### 2.4.2. Longitudinal Vehicle Dynamics

#### 2.4.3. Gearbox

Gear | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
---|---|---|---|---|---|---|---|

$ig$ | 15.943 | 10.038 | 6.359 | 4.335 | 3.205 | 2.501 | 1.995 |

η | 0.97 | ||||||

${T}_{0}$ | ${T}_{nom}\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}6\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{10}^{-3}$ |

#### 2.4.4. Generator

#### 2.4.5. Electric Motor

#### 2.4.6. Battery

Parameter | Value | Unit | Parameter | Value | Unit |
---|---|---|---|---|---|

${V}_{\text{oc},\text{cell}}$ | 3.3 | $\mathrm{V}$ | ${P}_{\text{max},\text{cell}}$ | 400 | $\mathrm{W}$ |

${Q}_{\mathrm{cell}}$ | 4.5 | $\mathrm{A}\mathrm{h}$ | η | 0.98 | - |

${R}_{\mathrm{cell}}$ | 5 | $\mathrm{m}$Ω | ${m}_{cell}$ | 205 | $\mathrm{g}$ |

#### 2.4.7. Vehicle Parameters

Vehicle | Hybrid | Conventional | |||
---|---|---|---|---|---|

Subcompact | Compact | Full-size | Full-size | ||

Mass base vehicle (kg) | 855 | 1313 | 1735 | 1735 | |

Mass hybridization (kg) | 41 | 55 | 69 | - | |

Mass gas (kg) | 12 | 18 | 24 | 24 | |

Mass gas tank (kg) | 35 | 53 | 70 | 70 | |

Total mass vehicle (kg) | ${m}_{\mathrm{v}}$ | 943 | 1439 | 1898 | 1829 |

Aerodynamic drag coefficient (-) | ${c}_{\mathrm{d}}$ | 0.25 | 0.27 | 0.25 | 0.25 |

Frontal area (${\mathrm{m}}^{2}$) | ${A}_{\mathrm{f}}$ | 2.18 | 2.19 | 2.21 | 2.21 |

Rolling friction coefficient ($\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}{10}^{3}$) | ${c}_{\mathrm{r}}$ | 6.5 | 6.5 | 6.5 | 6.5 |

Auxiliary power demand ($\mathrm{W}$) | ${P}_{\text{aux}}$ | 200 | 300 | 400 | 400 |

Wheel radius ($\mathrm{m}$) | ${r}_{\mathrm{w}}$ | 0.293 | 0.316 | 0.326 | 0.326 |

Wheel inertia ($\mathrm{k}\mathrm{g}{\mathrm{m}}^{2}$) | ${\Theta}_{\mathrm{w}}$ | 4 $\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}$ 0.74 | 4 $\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}$ 0.92 | 4 $\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}$ 1.05 | 4 $\phantom{\rule{0.166667em}{0ex}}\xb7\phantom{\rule{0.166667em}{0ex}}$ 1.05 |

Combustion engine displ. volume (L) | ${V}_{\mathrm{d}}$ | 0.8 | 1.2 | 2.0 | 2.0 |

Electric motor power (kW) | 12 | 16 | 20 | N.A. | |

Battery number of cells (-) | 42 | 56 | 70 | N.A. | |

Battery power (kW) | 16.8 | 22.4 | 28 | N.A. | |

Battery capacity (kWh) | 0.62 | 0.83 | 1.04 | N.A. | |

Gearbox nominal torque (Nm) | ${T}_{\mathrm{nom}}$ | 160 | 240 | 400 | 320 |

#### 2.4.8. Engine Scaling

#### 2.4.9. Gear Shifting

#### 2.4.10. Energy Management of Hybrid-Electric Vehicle

## 3. Results and Discussion

#### 3.1. Static Engine Measurements

#### 3.1.1. Consumption Measurements

#### 3.1.2. Nitrogen Oxide Emissions

**Figure 6.**Measured nitrogen oxide emissions (engine out). Measurements for the lean operating region on the left-hand side. Measurements for the stoichiometric operating region on the right-hand side. Emissions are given as a function of engine load; each line indicates one engine speed.

#### 3.1.3. Soot

**Figure 7.**Measured soot emissions (engine out), as a function of engine load, with each line indicating one engine speed.

#### 3.2. Vehicle Emulation Results

#### 3.2.1. Detailed Results

**Figure 8.**Measured vehicle emulation results for the Full-size car with hybrid-electric powertrain on the NEDC.

**Figure 9.**Measured vehicle emulation results for the Full-size car with hybrid-electric powertrain on the WLTP.

**Figure 10.**Measured vehicle emulation results for the Full-size vehicle with conventional powertrain on the NEDC.

**Figure 11.**Measured vehicle emulation results for the Full-size vehicle with conventional powertrain on the WLTP.

#### 3.2.2. Consumption Results

**Table 6.**Summary of the vehicle emulation experiments for all vehicles and driving cycles. Each measurement is repeated three times. The table shows the mean value together with the maximum/minimum deviation of all measurements from the mean value.

Vehicle | Cycle | ${CO}_{2}$ (g/km) | ${\eta}_{\text{ICE}}$ (%) | ${C}_{\mathrm{G}}$ (kg/100 km) | ${C}_{\mathrm{D}}$ (l/100 km) | ${r}_{G}$ (%) | $\mathsf{\Delta}SOC$ (%) | |
---|---|---|---|---|---|---|---|---|

Hybrid | Full-size | NEDC | 68.8${\phantom{\rule{4pt}{0ex}}}_{-0.2}^{+0.5}$ | 35.4${\phantom{\rule{4pt}{0ex}}}_{-0.2}^{+0.1}$ | 2.27${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.01}$ | 0.25${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.02}$ | 92.7${\phantom{\rule{4pt}{0ex}}}_{-0.4}^{+0.3}$ | +0.21${\phantom{\rule{4pt}{0ex}}}_{-0.06}^{+0.05}$ |

WLTP | 77.7${\phantom{\rule{4pt}{0ex}}}_{-0.3}^{+0.3}$ | 34.9${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.2}$ | 2.46${\phantom{\rule{4pt}{0ex}}}_{-0.02}^{+0.01}$ | 0.40${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.01}$ | 89.6${\phantom{\rule{4pt}{0ex}}}_{-0.3}^{+0.2}$ | +1.82${\phantom{\rule{4pt}{0ex}}}_{-0.16}^{+0.17}$ | ||

Compact | NEDC | 55.9${\phantom{\rule{4pt}{0ex}}}_{-0.3}^{+0.4}$ | 35.9${\phantom{\rule{4pt}{0ex}}}_{-0.2}^{+0.2}$ | 1.88${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.01}$ | 0.17${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.00}$ | 94.0${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.2}$ | +0.86${\phantom{\rule{4pt}{0ex}}}_{-0.07}^{+0.04}$ | |

WLTP | 63.9${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.1}$ | 35.9${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.0}$ | 2.12${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.00}$ | 0.22${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.00}$ | 93.2${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | +2.37${\phantom{\rule{4pt}{0ex}}}_{-0.19}^{+0.20}$ | ||

Subcompact | NEDC | 43.0${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.1}$ | 35.9${\phantom{\rule{4pt}{0ex}}}_{-0.1}^{+0.1}$ | 1.40${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.00}$ | 0.18${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.01}$ | 91.5${\phantom{\rule{4pt}{0ex}}}_{-0.4}^{+0.2}$ | +1.37${\phantom{\rule{4pt}{0ex}}}_{-0.03}^{+0.06}$ | |

WLTP | 49.5${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | 36.4${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | 1.67${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.00}$ | 0.14${\phantom{\rule{4pt}{0ex}}}_{-0.00}^{+0.00}$ | 93.1${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | +2.50${\phantom{\rule{4pt}{0ex}}}_{-0.14}^{+0.26}$ | ||

Conv. | Full-size | NEDC | 115.4${\phantom{\rule{4pt}{0ex}}}_{-1.2}^{+0.8}$ | 25.4${\phantom{\rule{4pt}{0ex}}}_{-0.2}^{+0.2}$ | 2.66${\phantom{\rule{4pt}{0ex}}}_{-0.04}^{+0.04}$ | 1.62${\phantom{\rule{4pt}{0ex}}}_{-0.04}^{+0.07}$ | 69.6${\phantom{\rule{4pt}{0ex}}}_{-1.2}^{+0.7}$ | N.A. |

WLTP | 109.1${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | 29.3${\phantom{\rule{4pt}{0ex}}}_{-0.0}^{+0.0}$ | 2.88${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.01}$ | 1.14${\phantom{\rule{4pt}{0ex}}}_{-0.01}^{+0.01}$ | 77.8${\phantom{\rule{4pt}{0ex}}}_{-0.2}^{+0.2}$ | N.A. |

Vehicle | Cycle | Fuel energy (J/m) | Emissions of ${CO}_{2}$ (g/km) | |||||
---|---|---|---|---|---|---|---|---|

Diesel | Gas-Diesel | Change (%) | Diesel | Gas-Diesel | Change (%) | |||

Hybrid | Full-size | NEDC | 1131 | 1226 | +8.4 | 82.9 | 68.8 | −17.0 |

WLTP | 1219 | 1371 | +12.5 | 89.4 | 77.7 | −13.1 | ||

Compact | NEDC | 924 | 1000 | +8.2 | 67.7 | 55.9 | −18.4 | |

WLTP | 1026 | 1140 | +11.1 | 75.3 | 63.9 | −15.1 | ||

Subcompact | NEDC | 708 | 764 | +7.9 | 51.9 | 43.0 | −18.1 | |

WLTP | 807 | 886 | +9.8 | 59.1 | 49.5 | −16.2 | ||

Conv. | Full-size | NEDC | 1614 | 1911 | +18.4 | 118.3 | 115.4 | −2.4 |

WLTP | 1635 | 1853 | +13.3 | 119.9 | 109.1 | −9.0 |

## 4. Conclusions

## Acknowledgments

## Conflict of Interest

## References

- International Energy Agency. CO
_{2}Emissions From Fuel Combustion, 2011; IEA Publications: Paris, France, 2011. [Google Scholar] - International Energy Agency. World Energy Outlook, 2011; IEA Publications: Paris, France, 2011. [Google Scholar]
- Semin, R. A technical review of compressed natural gas as an alternative fuel for internal combustion engines. Am. J. Eng. Appl. Sci.
**2008**, 1, 302–311. [Google Scholar] - Ott, T.; Zurbriggen, F.; Onder, C.; Guzzella, L. Cycle-averaged efficiency of hybrid electric vehicles. Inst. Mechan. Eng. Part D J. Automob. Eng.
**2012**, 227, 78–86. [Google Scholar] [CrossRef] - Serrano, D.; Bertrand, L. Exploring the Potential of Dual Fuel Diesel-CNG Combustion for Passenger Car Engine. In Proceedings of the FISITA World Automotive Congress, Beijing, China, 27–30 November 2012.
- Duffour, F.; Ternel, C.; Pagot, A. IFP Energies Nouvelles Approach for Dual Fuel Diesel-Gasoline Engines; SAE Technical Paper 2011-24-0065, doi:10.4271/2011-24-0065; IFP Energies Nouvelles: Rueil-Malmaison, France, 2011. [Google Scholar]
- Eichmeier, J.; Wagner, U.; Spicher, U. Controlling Gasoline low Temperature Combustion by Diesel Micro Pilot Injection. In Proceedings of the ASME International Combustion Engine Division Fall Technical Conference, Morgantown, WV, USA, 2–5 October, 2011.
- Königsson, F.; Stalhammar, P.; Angstrom, H. Characterization and Potential of Dual Fuel Combustion in a Modern Diesel Engine. In Presented at Commercial Vehicle Engineering Congress, Chicago, IL, USA, 13 September 2011.
- Ishiyama, T.; Kang, J.; Ozawa, Y.; Sako, T. Improvement of performance and reduction of exhaust emissions by pilot-fuel-injection control in a lean-burning natural-gas dual-fuel engine. SAE Int. J. Fuels Lubr.
**2012**, 5, 243–253. [Google Scholar] [CrossRef] - Papagiannakis, R.; Rakopoulos, C.; Hountalas, D.; Rakopoulos, D. Emission characteristics of high speed, dual fuel, compression ignition engine operating in a wide range of natural gas/diesel fuel proportions. Fuel
**2010**, 89, 1397–1406. [Google Scholar] [CrossRef] - Selim, M. Pressure–time characteristics in diesel engine fueled with natural gas. Renew. Energy
**2001**, 22, 473–489. [Google Scholar] [CrossRef] - Schmidt, T.; Weiskirch, C.; Lieske, S.; Manz, H. Modern industrial engines emission calibration and engine management. ATZ Highw.
**2010**, 9, 24–35. [Google Scholar] - Ott, T.; Zurbriggen, F.; Onder, C.; Guzzella, L. Cylinder Individual Feedback Control of Combustion in a Dual Fuel Engine. In Proceedings of the IFAC Advances in Automotive Control, Tokyo, Japan, 4–7 September 2013.
- Shafai, E. Fahrzeugemulation an Einem Dynamischen Verbrennungsmotor-Prüfstand. Ph.D. Thesis, ETH, Zurich, Switzerland, 1990. [Google Scholar]
- Dönitz, C.; Voser, C.; Vasile, I.; Onder, C.; Guzzella, L. Validation of the fuel saving potential of downsized and supercharged hybrid pneumatic engines using vehicle emulation experiments. J. Eng. Gas Turbines Power
**2011**, 133, 092801:1–092801:13. [Google Scholar] [CrossRef] - Schneeweiss, B.; Teiner, P. Hardware-in-the-loop-simulation am motorenprüfstand für realitätsnahe emissions- und verbrauchsanalysen [in German]. ATZextra
**2010**, 15, 76–79. [Google Scholar] - Chasse, A.; Sciaretta, A. Supervisory control of hybrid powertrains: An experimental benchmark of offline optimization and online energy management. Control Eng. Pract.
**2011**, 19, 1253–1265. [Google Scholar] [CrossRef] - Henning, G.; Gödecke, T.; Damm, A. Neue Getriebe für die neuen Kompakten [in German]. ATZextra
**2012**, 17, 70–73. [Google Scholar] [CrossRef] - Hadler, J.; Metzner, F.T.; Schäfer, M.; Gröhlich, H.; John, M. Das siebengang-doppelkupplungsgetriebe von volkswagen [in German]. ATZ Automob. Z.
**2008**, 110, 512–521. [Google Scholar] [CrossRef] - Pfaller, S.; Saal, A.; Wildgruber, M.; Bartusch, S. Intelligentes energiemanagement und effizienter generator [in German]. ATZextra
**2011**, 15, 36–41. [Google Scholar] - Guzzella, L.; Sciarretta, A. Vehicle Propulsion Systems, Introduction to Modeling and Optimization, 3rd ed.; Springer: Berlin, Germany, 2013. [Google Scholar]
- Bertsekas, D.P. Dynamic Programming and Optimal Control Volume I, 3rd ed.; Athena Scientific: Nashua, NH, USA, 2005. [Google Scholar]
- Sundström, O.; Guzzella, L. A Generic Dynamic Programming Matlab Function. In Proceedings of the 18th IEEE International Conference on Control Applications, Saint Petersburg, Russia, 8–10 July 2009.
- Sundström, O.; Guzzella, L.; Soltic, P. Optimal Hybridization in Two Parallel Hybrid Electric Vehicles using Dynamic Programming. In Proceedings of the 17th IFAC World Congress, Seoul, Korea, 6–11 July 2008.
- Ambühl, D. Energy Management Strategies for Hybrid Electric Vehicles. Ph.D. Thesis, ETH, Zurich, Switzerland, 2009. [Google Scholar]
- Hadler, J.; Rudolph, F.; Engler, H.J.; Röpke, S. Der neue 2,0-l-4V-TDI-Motor mit common-rail-einspritzung [in German]. MTZ Motortech. Z.
**2007**, 68, 914–923. [Google Scholar] [CrossRef]

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**MDPI and ACS Style**

Ott, T.; Onder, C.; Guzzella, L. Hybrid-Electric Vehicle with Natural Gas-Diesel Engine. *Energies* **2013**, *6*, 3571-3592.
https://doi.org/10.3390/en6073571

**AMA Style**

Ott T, Onder C, Guzzella L. Hybrid-Electric Vehicle with Natural Gas-Diesel Engine. *Energies*. 2013; 6(7):3571-3592.
https://doi.org/10.3390/en6073571

**Chicago/Turabian Style**

Ott, Tobias, Christopher Onder, and Lino Guzzella. 2013. "Hybrid-Electric Vehicle with Natural Gas-Diesel Engine" *Energies* 6, no. 7: 3571-3592.
https://doi.org/10.3390/en6073571