# Advances in Diesel-LNG Internal Combustion Engines
## 2 Results
### 2F Diesel-LNG ICEs R&D
From a pure pressure build-up perspective, HCCI also does not produce a peak pressure during the expansion stroke, being HCCI ICEs statistically limited to deliver peak pressure exactly at top dead center. Hence, the LNG must be injected at the center of the chamber and burned by the diesel injection before filling homogeneously all the chamber. This is possible with late, fast, high flow rate, injections of the LNG. Also, Westport HPDI is evolving towards more complex injection and combustion modes, where there is the opportunity of premixed and diffusion NG combustion but constrained using their patented large 2F injector. The major advantages of HPDI are the ability to do the injection of the diesel and the NG with a single injector. The major disadvantage of this approach, vs. the use of two dedicated injectors, one for the diesel and one for the NG, is the inability to achieve for the diesel same actuation times, injection pressure, atomization, and flow rates, of the latest single fuel diesel injectors, and certainly longer actuation times, smaller flow rates, and more constrained jet shapes, for the LNG, vs. a dedicated single fuel LNG injector, however presently unavailable off the shelf. It is the rate of injection that limits the diffusion combustion of the LNG. It is the actuation time and the rate of injection, to a lesser extent, that limit the amount of LNG that can be introduced to burn premixed. The injection profile and the heat release profile are linked to each other. Apart from the 2F diesel LNG DI injector by Westport, which is a high-tech, off-the-shelf product, other manufacturers have not developed competitive products in recent years. Hoerbiger developed a single fuel DI injector for hydrogen, a much more demanding than NG fuel that is at normal conditions, in the early 2000s during the attempts by BMW to produce a hydrogen car. However, the development of this injector ended with the end of the BMW project [44]. [PERSON] designed HP injectors for DI of hydrogen into the combustion chamber with pressures of up to 300-bar. These injectors were tested and calibrated at the Hydrogen Center Austria, which also supplied the hydrogen infrastructure for the project. To conclude, the latest development of 2F diesel LNG ICEs is to directly inject both fuels, in a chamber with suitable pressure and temperature, as resulting from advanced turbocharging, shaping the heat release rate curve to produce a pressure profile where:  
* Pressure must rise fast about TDC during the premixed combustion phase, but within limits for what concerns the dp/d0 and the TDC maximum pressure. * Pressure must continue to grow during the early expansion phase, to produce a peak pressure about 13-14 degrees crank angle after TDC. The peak pressure must be within acceptable limits. The fuel flow rate must be large enough during this phase. As the work during compression is negative, and only the work during expansion is positive, the amount of heat released during the premixed and diffusion phases must be carefully controlled to maximize the \(\eta\) within the constraints. An adequate fuel flow rate from the LNG DI injector, as well as the rate of actuation, are crucial to achieving the above goals. Further developments of 2F diesel LNG ICEs strongly depend on the ability to produce dedicated injectors allowing high flow rates, and fast actuation, with multiple injection capabilities, i.e., pretty much the same demand for the latest single fuel diesel injectors but for the reduced density cryogenic LNG. It must be added that the use of two injectors per cylinder is not certainly a problem of packaging, as diesel ICEs have easily accommodated a DI and a glow plug for many years until the further progress of DI has made the glow plug redundant, and gasoline DI, jet or spark positive ignition (PI) ICEs adopt one DI injector plus the jet ignition (JI) device or the spark plug (SI) with much larger intake and exhaust valves than the CI diesel ICEs.